CLIMATE OF PHOENIX, ARIZONA: An Abridged On-Line Version of NOAA Technical Memorandum NWS WR-177

by

Robert J. Schmidli

Weather Service Forecast Office
Phoenix, Arizona

First Printed April 1969 as WR-38
Revised and Reprinted as WR-177, March 1983 and
December 1986

May 1996 (Revised)
On-Line Version by R.S. Cerveny, Office of Climatology, ASU (December, 1996)



This publication has been reviewed and is approved for publication by Scientific Services Division, Western Region.

CONTENTS


Abstract
General Geographical and Climatological Summary
Climatological Summary by Month
History of Weather Observations
Elevations at National Weather Service Forecast Office

Temperature
Normal Maximum, Minimum and Mean by Months

  • Highest Mean and Lowest Mean by Months and Year of Occurrence
  • Highest and Lowest Mean Maximum and Highest and Lowest
  • Greatest # of Consecutive Months Above and Below Normal
  • Highest Maximum and Lowest Minimum by Months and Day and Year of Occurrence
  • Lowest Maximum and Highest Minimum by Months and Day and Year of Occurrence
  • Greatest and Least Monthly Temperature Range by Months and year of Occurrence
  • Hottest and Coolest Summers and Warmest and Coldest Winters
  • Hottest 3 and 2 Consecutive Months
  • Hottest Single Months
  • Warmest & Coldest Winters
  • Coldest 2 consecutive and Single Months Humidity

    Dew Point Temperature
    Highest Hourly Dew Points
  • Highest Daily Dew Points
  • Highest Monthly Dew Points
  • Lowest Hourly Dew Points
  • Lowest Daily Dew Points
  • Lowest Monthly Dew Points
  • Lowest Relative Humidities
    Heat Index (Apparent Temperature)
  • Air Temperature / Relative Humidity
  • The Myth of Increasing Moisture Levels in Phoenix
  • Average Temperature & Relative Humidity in Percent by Five-Year Periods

  • Temperature Records
  • Average Number of Days of 100 or Higher by Months, and Earliest and Latest Date of Occurrence
  • Average Number of Days of 110 or Higher by Months and Earliest and Latest Date of Occurrence
  • Probability in Percent of Observing 100 or Higher, 105 or Higher, and 110 or Higher
  • Greatest Number of Consecutive Days with 120 or Higher, 115 or Higher, 110 or Higher, 105 or Higher, 100 or Higher, and 99 or Higher
  • Greatest Number of Consecutive Days with Maximum 75 or Lower, 60 or Lower, 55 or Lower, 50 or Lower, 45 or Lower, and 42 or Lower
  • Greatest Number of Days in One Year with Maximum 90 or Higher, 100 or Higher, 105 or Higher, 110 or Higher, 115 or Higher, and 120 or Higher
  • Least Number of Days in One Year with Maximum 90 or Higher, 100 or Higher, 105 or Higher, and 110 or Higher
  • Greatest Number of Consecutive Days with Minimum 35 or Lower, 32 or Lower, 30 or Lower, 28 or Lower, 25 or Lower, and 20 or Lower
  • Greatest Number of Days in One Winter with Minimum 32 or Lower, 28 or Lower, 24 or Lower, and 20 or Lower
  • Least Number of Days in One Winter with Minimum 32 or Lower
  • Greatest Number of Consecutive Days with Minimum 85 or Higher and 80 or Higher
  • Greatest Number of Days in One Year with Minimum 85 or Higher and 80 or Higher71
  • Greatest Number of Consecutive Days with Mean 100 or Higher
  • Greatest Number of Days in One Year with Mean 100 or Higher
  • Highest and Lowest Daily Mean
  • Greatest and Least Daily Temperature Range
  • Normal and Highest and Lowest Heating Degree Days by Months and Year of Occurrence (Base 65 Degrees)
  • Normal and Highest and Lowest Cooling Degree Days by Months and Year of Occurrence (Base of 65 Degrees)
  • Average and Highest and Lowest Cooling Degree Days by Months and Year of Occurrence (Base 80 Degrees)
  • Freeze and Growing Season Data

    Precipitation
    Normal Total and Maximum and Minimum Total by Months and Year of Occurrence
  • Years in Which There Were 5 (the most) Calendar Months Without Measurable Precipitation
  • Years in Which All Twelve Calendar Months had Measurable Precipitation
  • Daily Normals of Precipitation
  • Greatest Number of Days with Trace or More and 0.01 Inches or More by Months and Year of Occurrence and Average Number of Days with 0.01 Inches or More by Months
  • Greatest Number of Days with 0.10 Inches or More, 0.50 Inches or More, and 1.00 Inch or More by Months and Year of Occurrence
  • Maximum Amounts for 5, 10, 15, and 30 Minutes; 1, 2, and 24 Hours by Months and Day and Year of Occurrence
  • Greatest Number of Consecutive Days with Trace or More, 0.01 Inches or More, 0.25 Inches or More, 0.50 Inches or More, and 1.00 Inch or More
  • Greatest Number of Consecutive Days without Trace or More and without 0.01 Inches or More
  • Amounts and Dates of All Snowfalls
  • Daily Frequency of Occurrence in Percent of Trace or More, 0.01 Inches or More, 0.10 Inches or More, 0.25 Inches or More, 0.50 Inches or More, and 1.00 Inch or More
  • Frequency of Occurrence of 0.01 Inches or More on Consecutive Days
  • Estimated Return Periods for Short-Duration Precipitation
  • Monthly and Annual Precipitation, Monthly and Annual Greatest 24-hour Precipitation

    Thunderstorms, Hail & Tornadoes
    Arizona Monsoon: Discussion
  • Monsoon Statistics (Average Dates of Start, End, etc.)
  • Monsoon Start & End Dates: 1948-1995
  • Wettest & Driest Monsoons
  • Average Number of Days with Thunderstorms by Months and Average Number of Days with Hail by Months
  • Greatest Number of Days with Thunderstorms and Greatest Number of Days with Hail by Months and Year of Occurrence - 1896-1990
  • Frequency of Thunderstorm Occurrence in Percent by Days

    Lightning Information

    Description of Known Tornadoes and Funnel Clouds in the Greater Phoenix Area - 1955-1990

    Sunshine, Cloudiness, and Fog
    Average and Highest and Lowest Percentage of Possible Sunshine by Months and Year of Occurrence
  • Average Annual Percentage of Possible Sunshine at Phoenix as Compared to other Major U. S. Cities
  • Average Number of Clear, Partly Cloudy, Cloudy, and Heavy Fog Days by Months
  • Greatest Number of Consecutive Days with 100 Percent Sunshine and 0 Percent Sunshine

    Wind
    Average Speed and Prevailing Direction by Months and Peak Gust by Months and Day and Year of Occurrence
  • Mean Frequency of Occurrence of Peak Gusts by Months
  • Estimated Return Periods of Peak Wind Gusts by Months

    Pressure
  • Average and Highest and Lowest Station Pressure by Months and Day and Year of Occurrence
  • Highest and Lowest Sea-Level Pressure by Months and Day and Year of Occurrence
  • Normal 6-Hourly Pressure Changes in Inches

    Flying Weather
    Percentage Frequencies of Ceiling-Visibility
  • Frequencies of Visibility-Restricting Phenomena by Months

    Holiday Weather Information
  • Average Maximum and Minimum Temperature, Highest Maximum and Lowest Minimum and Year of Occurrence, and Frequency of .01 Inches or More of Precipitation in Percent on Various Holidays

    Weather Extremes
  • Weather Extremes of Temperature, Precipitation, Snowfall, Pressure, and Wind for Phoenix as Compared to Those of Arizona and United States

    CLIMATE OF PHOENIX: PART 1

    ABSTRACT


    The purpose of this publication is to provide comprehensive data on the climate of Phoenix. It is hoped that these data will help residents, visitors, prospective residents, agriculturalists, engineers, community planners, Chambers of Commerce, the movie industry, etc., make more skillful decisions affecting their lives, their plans for the future, and hence the whole economy of the area. Data in this revision are for the period January 1, 1896 through December 31, 1995. This marks 100 years of continuous weather records for Phoenix.

    The assistance given by Mr. Robert S. Ingram, former Meteorologist in Charge, National Weather Service Office, Phoenix, Arizona, Mr. Paul C. Kangieser, former NOAA Climatologist for Arizona, and other staff members is gratefully acknowledged. The writer is gratefully indebted to Mr. Harold C. Bulk, former Assistant State Climatologist, Office of Climatology, Arizona State University, for his article, "An Overview of Phoenix Climate". Ms. Brazel and Mr. Balling's research paper, "The Myth of Increasing Moisture Levels in Phoenix", is also included in this Technical Memorandum.

    I. GENERAL GEOGRAPHICAL AND CLIMATOLOGICAL SUMMARY


    Phoenix is located in about the center of the Salt River Valley, a broad, oval-shaped, nearly flat plain. The Salt River runs from east to west through the valley, but, owing to impounding dams upstream, it is usually dry. The climate is of a desert type with low annual rainfall and low relative humidity. Daytime temperatures are high throughout the summer months. The winters are mild. Nighttime temperatures frequently drop below freezing during the three coldest months, but the afternoons are usually sunny and warm.

    At an elevation of about 1100 feet, the station is in a level or gently sloping valley running east and west. The Salt River Mountains, or South Mountains as they are commonly called, are located 6 miles to the south and rise to 2600 feet MSL. The Phoenix Mountains lie 8 miles to the north with Squaw Peak rising to 2600 feet MSL. The famous landmark of Camelback Mountain lies 6 miles to the north-northeast and rises to 2700 feet MSL. Eighteen miles to the southwest lie the Sierra Estrella Mountains with a maximum elevation of 4500 feet MSL, and 30 miles to the west-northwest are found the White Tank Mountains with a maximum elevation of 4100 feet MSL. The Superstition Mountains are approximately 35 miles to the east and rise to 5000 feet MSL.

    The central floor of the Salt River Valley is irrigated by water from dams built on the Salt River system. To the north and west of the gravity flow irrigated district, there is considerable agricultural land irrigated by pump water.

    There are two separate rainfall seasons. The first occurs during the winter months from November through March when the area is subjected to occasional storms from the Pacific Ocean. While this is classified as a rainfall season, there can be periods of a month or more in this or any other season when practically no precipitation occurs. Snowfall occurs very rarely in the Salt River Valley, while light snows occasionally fall in the higher mountains surrounding the valley. The second rainfall period occurs during July and August when Arizona is subjected to widespread thunderstorm activity whose moisture supply originates in the Gulf of Mexico, in the Pacific Ocean off the west coast of Mexico and in the Gulf of California.

    The spring and fall months are generally dry, although precipitation in substantial amounts has fallen occasionally during every month of the year.

    During the winter months, the temperature is marginal for some types of crops. Areas with milder temperatures around the edges of the valley are utilized by these crops. However, the valley is subjected to occasional killing and hard freezes in which no area escapes damage.

    The valley floor, in general, is rather free of strong wind. During the spring months southwest and west winds predominate and are associated with the passage of low-pressure troughs. During the thunderstorm season in July and August, there are often local, strong, gusty winds with con­siderable blowing dust. These winds generally come from a northeasterly to southeasterly direction. Throughout the year there are periods, often several days in length, in which winds remain under 10 miles per hour.

    Sunshine in Phoenix area averages 86 percent of possible, ranging from a minimum monthly average of around 78 percent in January and December to a maximum of 94 percent in June. During the winter, skies are sometimes cloudy, but sunny skies predominate and the temperatures are mild. During the spring, skies are also predominately sunny with warm temperatures during the day and mild pleasant evenings. Beginning with June, daytime weather is hot. During July and August, there is an increase in humidity, and there is often considerable afternoon and evening cloudiness associated with cumulus clouds building up over the nearby mountains. Summer thunder­showers seldom occur in the valley before evening.

    The autumn season, beginning during the latter part of September, is characterized by sudden changes in temperature. The change from the heat of summer to the mild winter temperatures usually occurs during October. The normal temperature change from the beginning to the end of this month is the greatest of any of the twelve months in central Arizona. By November, the mild winter season is definitely established in the Salt River Valley region.

    An Overview of Phoenix Climate



    By Harold Bulk, Office of Climatology, Arizona State University

    The climate of a location is the synthesis of several elements. The temporal variations of several of these elements is shown in the graph on the following page.

    The temperature of the air is probably the element that most people are aware of. Yet air temperature is the result of many other climatic elements. The most important is the receipt of solar energy, for solar energy is the force that drives most of the other climatic elements. The daily amounts of solar energy that are received at the top of the atmosphere (the extra-terrestrial radiation, or ETR) is shown in curve A. The amounts vary from nearly a thousand Langleys (1 Langley = 1 calorie per square centimeter) on the day of the Summer Solstice to about 400 Langleys on the day of the Winter Solstice. Clouds reflect a substantial portion of the solar energy. More is absorbed by water vapor in the air, and even the atmosphere itself will scatter a portion of the solar energy back to space as well as absorb a portion.

    Curve C represents the amount of energy that can reach Phoenix on a clear, dry day. (Rosendahl, 1976). It is apparent that only about 70% of the ETR reaches the surface under these conditions. The ten-year average daily receipt of solar energy at Phoenix is shown in curve D.


    Some of the energy reaching the earth's surface is reflected back toward space by the earth itself, some is used to evaporate water, and the remainder warms the air. The large drop in energy receipt during July is directly traceable to the increase in cloudiness (curve E) during this period. (The depletion of solar energy due to clouds is also apparent during the winter months, although less spectacularly so). The continued depression of the averaged receipts of solar energy into August is due to the increased water vapor in the atmosphere (curve F, from Reitan, 1960). The increased water vapor in the atmosphere is due to a shift in the winds from a predom­inantly westerly direction to a southerly direction, the so-called "Arizona Monsoon". Although the dry bulb temperatures may be depressed during this period, the "sensible temperatures" seem higher due to the increased humidity of the air.

    Also shown is the ten-year average daily precipitation at Phoenix (curve G). It is seen that the largest average daily receipts occur in July and August. Rainfall plays a significant role in that a portion of the solar energy reaching the ground is used to evaporate moisture.

    Curve B is the average daily temperature at Phoenix. This curve lags the curves for ETR (A), that of clear-day receipts (C), and that for averaged receipts (D). This is due primarily to the thermal lag of the earth. The flattening of the temperature curve during August is due to the energy absorbed by the enhanced rainfall during that time.

    Clearly, the daily average temperature at Phoenix is the result of primarily the solar energy reaching the earth's surface and the precipitation regime.

    References



    Local Climatological Data, Monthly for Phoenix, Arizona. NOAA, EDIS, Asheville, North Carolina, 1971-1980.

    National Weather Service Forecast Office, Phoenix, Arizona. Daily total Horizontal Solar Energy Receipts, 1971-1980.

    Reitan, C.H., 1960: "Distribution of Precipitable Water Vapor over the Continental United States". Bulletin American Meteorological Society, 41, 79-87.

    Rosendahl, H. 1976: "Table of daily Values of Maximum Possible Solar Energy, in Solar Radiation and Sunshine Data for the Southwestern U.S.". R. Durrenberger, Editor, Tempe, Arizona, Laboratory of Climatology.

    II. CLIMATOLOGICAL SUMMARY BY MONTHS

     

    1. January Weather


    The Phoenix area generally experiences its coldest weather in January, yet, daytime temperatures still average in the middle sixties. The normal daily maximum is 65.9, and the normal daily minimum 41.2 and the normal mean monthly temperature is 53.6.

    The warmest January occurred in 1986 when the mean monthly temperature was 61.4; the coldest was in 1937 with a mean temperature of only 43.2. The highest temperature ever recorded in any January was 88 on the 19th in 1971. The lowest January temperature (and the all-time low for Phoenix) was 16 on January 7, 1913. The warmest night occurred on the 27th in 1988 when the temperature fell no lower than 61. The record cold day for January and for any winter month was January 6, 1913, when the high, low, and mean temperatures were 39, 17, and 28, respectively.

    The relative humidity for the month averages about the same as that for December. The low value in the afternoon averages around 33 percent.

    The mean hourly surface wind speed is around 5.3 m.p.h., and the prevailing direction is from the east. The peak gust was 60 m.p.h. from the west on January 27, 1983.

    Precipitation during the month normally totals 0.67 inches, but it has ranged from 5.22 in 1993 to none in 1912, 1924, and 1972. The greatest amount of precipitation in 24 hours was 1.84 inches which occurred on January 10-11, 1993. There are normally four days with 0.01 inches or more, but January 1993 had fourteen such days.

    Snow can occur in January, but it is unusual. Snow in amounts of up to 1 inch has been reported at the official observing station on seven January days since 1896. The heaviest falls of just 1 inch fell in 1933 and 1937. On January 20-21, 1937, amounts up to 4 inches fell in parts of the city and some remained on the ground in shaded areas until the 23rd and 24th.

    The mean monthly percentage of possible sunshine is 78 percent. The greatest amount ever recorded was 100 percent in 1924, and the least was 54 percent in 1935.

    There are normally 14 clear days, 7 partly cloudy days and 10 cloudy days in the month. The greatest number of clear days was 27 in 1924 and 1925, while the greatest number of cloudy days was 22 in 1957.

    2. February Weather


    February begins the spring months where warm weather gradually returns to the Desert Southwest. High temperatures slowly rise from a normal of 68 at the beginning of the month to 73 at the end of the month, and nighttime temperatures moderate from 43 to 46. Nevertheless, a nighttime freeze is still a threat in February and into early March. Freezing temperatures can be expected on 3 or 4 nights during February across the valley.

    Temperatures in the 90s can occur in February, but such occurrences are unusual. The highest ever was 92 on the 25th in 1921 and on the 27th in 1986, and dropped as low as 24 on the 7th in 1899 and on the 8th in 1933. The coldest February on record was in 1939 with a mean temperature of 48.6 and the warmest was 66.0 in 1991.

    The normal rainfall for the month is 0.68 inches, and usually there are four days with 0.01 inches or more of rain. The month can be counted on to have at least one day with a thunder­storm, but in 1931 there were five days with thunderstorms. As much as 4.64 inches of rain have been measured in February back in 1905 and none fell in 1912, 1967, and 1984. There was 0.5 inches of snow on February 2, 1939, and a trace on three other days of the same month. A trace also fell on three consecutive days in February 1985 and a trace in 1994.

    There are usually 13 clear days, 7 partly cloudy days, and 9 cloudy days with an expectancy of 80 percent sunshine during the month.

    3. March Weather


    In March temperatures begin to warm noticeably. The average daily high temperature rises from 73 to 79 during the month and temperatures above 85 are not uncommon in the last days. At the same time, average daily low temperatures rise from 47 to 52. However, it should be remembered that even by the end of the month there is still a 20-percent chance of a 32 degree temperature in the coldest sections of the valley.

    The normal mean temperature for the month is 62.2. The warmest March on record occurred in 1972 when the average temperature was 70.6, and the coldest occurred in 1897 with 54.3 degrees. The highest temperature ever recorded on a March day was 100 on the 26th in 1988. The lowest temperature was 25 on the 4th in 1966. Some March days can still be cold, and a high temperature of only 49 was observed on the 2nd in 1915. At the other extreme, the temperature did not fall below 74 on the 28th in 1986. This is warm even for early summer.

    Rainfall, during March, averages 0.88 inches. As much as 4.82 inches was measured in 1941, and none was recorded in 1933, 1956, 1959, and 1984. Four days with measurable rain can be expected during the month, but in 1905 there were twelve such days.

    Snow has been observed only four times since 1896. Two-tenths of an inch fell on the 12th in 1917, and a trace fell on the 3rd in 1976, and on the 21st and 27th in 1991.

    The month averages 9 cloudy days but has had as many as 15 in 1966. There was only 1 cloudy day in 1917 and 1988. Although not especially a sunny month, March still averages about 84 percent of possible sunshine. In 1988, there was 99 percent sunshine, and in 1935 there was a little as 60 percent.

    4. April Weather


    Elsewhere in the nation, April is greeted generally as the first month of spring:

    "April and May are the keys of the year".
    "April showers bring May flowers", etc.


    But in Phoenix, spring has been under way for some time before April makes its appearance. The average high temperature rises from 80 at the beginning of the month to 89 by the end. One-hundred degree temperatures are unusual. In 1989 a 105 degree temperature was recorded on the 20th and on the 29th in 1992. The average number of days with temperatures of 100 or higher is less than one. Many years have none at all, but there were nine days with 100 or higher in 1989. Nighttime temperatures rise from an average of 52 on the 1st to 59 on the 30th.

    The mean temperature for the month is 69.9, and it has been as warm as 80.1 in 1989 and as cold as 62.4 in 1967.

    April's rainfall continues the downward trend toward the May minimum, and the normal is only 0.22 inches. In 1926, 3.36 inches fell, and the last April without any rain was in 1993. Over the years, however, the month averages two days with measurable rain. The most measurable rain days occurred in 1926 with 13.

    Winds become a bit more gusty in April with the increase in heating, and gusts on the order of 20 to 24 m.p.h. or higher can be expected on eight days and even gusts of 40 to 44 m.p.h. on one day.

    April's sunshine averages 89 percent of possible, reaching a high value of 98 percent in 1954, 1961, 1989, and 1991, and a low of 68 percent in 1926.

    Six cloudy days can be expected, but there were as many as twelve in 1959. The last April with no cloudy days occurred in 1920.

    5. May Weather


    James Russell Lowell said in Under the Willows, "May is a pious fraud of the almanac". In Phoenix this is only too true! In most sections of the Nation, May brings true spring weather; but in the Desert Southwest, it signals the beginning of the long hot summer.

    The average date of the first 100-degree temperature is May 14th. Such a temperature reading has been observed only once as late as June 18th in 1913, and 100-degree temperatures are not spring-like!

    The average high temperature is 93.6, and the average low temperature is 63.9. The temperature has reached as high as 114 on the 30th in 1910 and has dipped as low as 39 on the 3rd in 1899. Fortunately, these are rare exceptions.

    May signals the beginning of the dry season. The month averages only 0.12 inches of rain and is the driest month of the year. The most rain ever recorded in May was 1.31 inches in 1930. The month averages only one day with 0.01 inches or more of rain, and it has had as many as seven such days, but no more. This happened in 1992. In contrast, there were 14 rainy days in February 1905. Thunderstorms occur on the average of once a month, but few can be seen in the distance on about three other days in the month.

    Cloudy days are unusual and occur on only about four days. Sunshine on the average reaches the 93 percent level. Never has any May had less than 79 percent of possible sunshine, which was in 1992.

    At the same time, May humidities, like June, are generally extremely low in comparison with those of July and August. Perhaps May should be appreciated more than it is because it is nature's way of conditioning residents for the steamy summer season of higher temperatures and humidities.

    6. June Weather


    June is the 2nd driest and one of the three hottest months of the year. The normal rainfall amounts to only 0.13 inches, but as much as 1.70 inches was measured in 1972. There is usually only one day when 0.01 inches or more of rain falls, and the greatest number of such days was only four. This happened only twice, in 1899 and 1932.

    The normal mean temperature for the month is 88.2 and has ranged from 93.8 in 1990 down to 79.0 in 1965. In early June, the normal daily high temperature reaches 100 or higher and stays there until the middle of September. Average nighttime temperatures rise from 68 on the 1st to 78 on the 30th. However, on the 27th in 1990, the temperature did not fall any lower than 93. The month averages three days of 110 degrees or higher, but in 1974 there were eighteen such days. The highest temperature ever recorded at Phoenix was 122 degrees on June 26, 1990.

    Despite the increasing heat, the air is very dry with the relative humidity even slightly lower than that of May and the lowest of the year. Afternoon readings on the average dip as low as 11 percent. Sunshine is at its maximum and averages 94 percent. June 1916, 1917, 1928, and 1939 all had 100 percent sunshine. The lowest ever recorded was 78 percent in 1931. There are usually only two cloudy days, and the most that has ever been observed was six in 1956.

    Toward the end of June, more thunderstorms become visible in the distance along the mountains heralding the arrival of the annual Arizona monsoon, that hot and humid period of midsummer.

    7. July Weather


    July is the month in which the Arizona monsoon usually arrives from the subtropical latitudes. This monsoon features an inflow of a deep blanket of moisture along with the usual summer high temperatures. A useful definition of a "monsoon day" for the Phoenix area is any day during which the average of the hourly dew point temperatures equals or exceeds 55 degrees F. Over the period of record, the average date of the first day of this event is July 7th.

    The monsoon season generally begins in early July and extends through the middle of September; however, it began as early as June 16th in 1925 and as late as July 25th in 1987. The monsoon is not necessarily a permanent feature but may come and go, giving residents brief respites from the muggy weather. On the average there are about 20 monsoon days in July, but there were as many as 31 days in 1984 and as few as seven days in 1987.

    Increased thunderstorm activity accompanies the arrival of the monsoon. Thunderstorms are visible on the average during 25 days of the month. On six or seven of these days, the storms are close enough for thunder to be heard at Sky Harbor International Airport. Dust storms associated with these thunderstorms are rather common.

    With the increase in thunderstorm activity comes an increase in rainfall. The average for the month is 0.83 inches, but 6.47 inches fell in 1911. The month averages four days with 0.01 inches or more of rain but has had as many as thirteen days in 1896. The probability of a trace or more of rain on any particular day rises from 21 percent on the first of the month to a peak of 54 percent during the last ten days as the monsoon influence intensifies. July is the windiest month of the year with an average velocity of 7.1 m.p.h.

    July's average temperature of 93.5 degrees is the highest of the year, and the month features an average high temperature of 105.9 and an average low of 81.0. The temperature has reached as high as 121 on the 28th in 1995. The lowest ever recorded was 63 on the 4th and 5th in 1912. There are usually 26 days with 100 or higher and five days with 110 or higher during the month. In 1989, there were 16 days with 110 or higher. Nighttime temperatures generally fall to around 80, however, it did not fall below 93 on the 20th in 1989.

    8. August Weather


    By August the summer heat begins to moderate slightly, but humidities are higher than in July. This makes many residents feel that it is much hotter than it really is. Actually, the average high temperature is 103.7 or 2.2 degrees lower than in July.
    August still averages 23 days with temperatures of 100 or higher and 2 days of 110 or higher. It has had as many as 31 days of 100 or higher in 1973 and 1975 and in several earlier years. There were as few as 9 such days in 1955. In 1995, there were 10 consecutive days of 110 or higher.

    Rainfall in August averages 0.96 inches, the second highest of any month of the year. The most rain ever recorded in August was 5.33 in 1951 and the least was a trace in 1973 and 1975. July is the only other month that always has had some rain.

    Thunderstorms and "dusters" are most frequent in August with an average of 7 thunderstorm days, and thunderstorms clouds are usually visible on 24 days of the month.

    Sunshine averages 85 percent during the month, but there are usually 4 cloudy days. In 1957 there were 10 cloudy days, and in 1953 and several other years there were none.

    9. September Weather


    September usually signals the end of the monsoon season. Although the long sustained periods of high humidity that occur principally in July and August may have ended, periods of high humidity do still occur in September. Twelve days in the month can usually be classified as monsoon days.

    The average monthly temperature is 85.6 or 7.9 degrees lower than that of July. On the 1st of the month the average high is 102 and the low 77; by the 30th the average high is down to 94 and the low 68. Readings of 110 or higher are uncommon, but there were four such days in 1945 and 1982, and a reading of 116 was observed on the 1st in 1950. The hot weather is not completely over as there usually are on the average 13 days with 100 or higher during the month. The average date of the last 100 degree temperature is the 27th. The lowest temperature ever recorded was 47 on the 20th and 21st in 1965.

    Rainfall averages 0.86 inches. The most ever recorded was 5.41 inches in 1939, and the least was none in 1953, 1957, 1968, 1973, and 1988. The month averages three days with 0.01 inches or more, but in 1939 there were nine such days.

    There are usually four days with thunderstorms and nine other days when thunderstorms are visible over the surrounding mountains.

    The rainfall patterns change in September from the evening thunder­shower pattern of the monsoon season to a more generally distributed pattern more typical of the winter months.

    There are usually three cloudy days, which next to June's two days, make it one of the least cloudy months of the year. Sunshine averages 89 percent of possible.

    10. October Weather


    During the month of October, weather is generated more from storm activity over the Pacific Ocean than from the subtropical moisture. High pressure systems that bring Indian Summer to the eastern sections of the Nation pass across the Great Basin area to the north, and dry, cold fronts often pass southward across Arizona, drying out and cooling the air.

    The average temperature for the month is 74.5 or 19.0 degrees cooler than July. Daytime high temperatures usually begin the month at 94 but cool off to 82 by Halloween. Nighttime low temper­atures drop from 67 to 54. These are the largest changes in normal high and low temperatures that occur during any month of the year. Record temperature extremes for the month range from 107 in 1980 to 34 in 1971. October does average one day each year with at least 100 or higher. The latest in the season that a temperature of 100 or higher has ever occurred was October 20, 1921.

    Rainfall amounts to only 0.65 inches on the average. Rain falls more evenly during the 24 hours in contrast to the summer months when it is concentrated during the night.

    The most rain that ever fell since records began was 4.40 inches in 1972. There is usually one thunderstorm day during the month.

    The month averages four cloudy days. It averages 88 percent of possible sunshine and has never had less than 65 percent.

    On the whole, October is a magnificent month with enough of the summer warmth to make outdoor living the most enjoyable of the year and yet with enough coolness to make it invigorating.

    11. November Weather


    With November usually comes the first 32 degree temperatures or below in the valley. Although the average date of such occurrence is December 12th at Sky Harbor International Airport, it usually occurs by:

    November 21 in Buckeye
    22 in Tempe
    23 in Litchfield Park
    ...............24 in Mesa
    ...............25 in Deer Valley

    The average temperature for the month is 61.9. Daytime high temperatures at the beginning of the month usually are about 81 and nighttime lows are normally 54. By the end of the month these temperatures have dropped to 70 and 44, respectively. The highest reading was a 96 on the 1st and 2nd in 1924, and the lowest was 27 on the 23rd in 1931.

    By November the area is definitely under the influence of weather systems of more northern latitudes, and rainfall averages 0.66 inches. The most rainfall ever recorded was 3.61 inches in 1905, and the last time that no rain fell during the month was in 1980.

    Snow has been observed only once since 1896. One-tenth of an inch was measured on the 28th in 1919.

    Sunshine averages 83 percent of possible. However, there has been as much as 98 percent reported in 1948 and 1956 and as little as 62 percent in 1965 and 1982. On the average there are 18 clear days, 6 partly cloudy days, and 6 cloudy days.

    The average wind velocity for the month is 5.3 m.p.h., and the strongest peak gust ever recorded was 60 m.p.h. on the 30th in 1982.

    Unlike other sections of the Nation, this month is not the melancholy time that precedes the depressing winter months, but rather it is an invigorating month of sparkling days and cool nights.

    12. December Weather


    By December, freezing temperatures in the valley are rather common, and freezing temperatures can be expected somewhere in the area on fifteen to twenty days of the month.

    High daytime temperatures on the first of the month are about 69 and taper off slowly to 65 by the end of the month. Nighttime temperatures drop from 44 to 40. The highest temperature ever recorded was 87 on the 10th in 1950, and the lowest was 22 on the 31st in 1900 and on the 26th in 1911.

    Total rainfall for the month averages 1.00 inch and is the highest of any month of the year. There are usually four days with 0.01 inches or more. Pacific storm systems move a little farther south, bringing more moisture to replenish the water supply with snows in the mountains. The most rain recorded was 3.98 inches in 1967, and the least was none in 1900, 1901, 1917, 1958, 1973, and 1981.

    A trace of snow has been reported on eight December days since 1896; 0.1 inches fell on the 11th in 1985, and 0.2 inches on both the 21st and 22nd in 1990.

    Sunshine now averages 77 percent with nine cloudy days. There was 98 percent of possible observed in 1958 and as little as 47 percent in 1914.

    III. HISTORY OF WEATHER OBSERVATIONS


    In the 1800s when communications in the United States were improved by the development of the railroads and telegraph, the practice of predicting weather from purely local signs and the haphazard measuring of meteorological phenomena began to decline. Scientists had noted correlations between the weather in one section of the country on a particular day and that in another section on the succeeding day. It was soon realized that a simul­taneous knowledge of weather conditions all over the country could conceivably enable man to predict storms of major consequences, and that warnings from such predictions could save countless lives and protect property investments. But it was not until the late 1860s that mounting public interest in a national weather service culminated in the signing into law by President Grant on February 9, 1870, of a resolution providing for meteorological observations at all military stations within the United States.

    The selection of the U.S. Army Signal Service to take such observations was dictated by the availability of communications facilities which the Signal Service had developed during the Civil War and were continuing to develop for protection against the Indians after the war. The original weather services provided by the military organi­zation covered only the Gulf and Atlantic Coasts and the Great Lakes. Another Act of Congress, on June 10, 1872, extended these services throughout the entire United States.

    Weather observations had been taken at many Army posts in Arizona prior to these formalities by Army Post Surgeons. Observations are available from some of these locations today:

    Station

    County

    Data Began

    Fort Defiance

    Apache

    December 1, 1851

    Camp Crittenden

    Santa Cruz

    December 1856

    Fort Mohave

    Mohave

    June 1859

    Fort Grant

    Graham

    December 1, 1860

    Camp Goodwin

    Graham

    August 1864

    Fort Whipple (Prescott)

    Yavapai

    January 1865

    Fort McDowell

    Maricopa

    September 1, 1866

    Camp Wallen

    Cochise

    November 1866

    Camp Date Creek

    Yavapai

    January 1867

    Fort Bowie

    Cochise

    August 1, 1867

    Camp Willow Grove

    Mohave

    November 1867

    Camp Reno

    Gila

    February 1, 1868

    Fort Verde (Camp Verde)

    Yavapai

    February 1, 1868

    Camp Hualapai

    Yavapai

    December 1869

    Fort Yuma

    Yuma

    January 1, 1870


    Observations from these stations were primarily temperature and rainfall. It wasn't until 1891, when the U.S. Weather Bureau was established, that development of reporting stations proceeded with cautious economy.

    The Bureau directed its attention mainly toward establishing a network of field stations. Faced with the growth of public interest, civic pride and the need to provide the best coverage for its forecasting and warning services with limited funds, the Weather Bureau could only slowly grant requests to establish weather stations in a rapidly expanding Nation.

    The first Weather Bureau Office to open in Arizona was in Yuma where the duties were transferred from the Army at Fort Yuma in July 1891. Tucson followed in September of that year, and it was not until four years later that the small community of Phoenix rated a full station. Records had been kept in Phoenix by the Signal Service beginning on January 28, 1876, and Signal Service personnel continued to take observations until they transferred the station on the corner of Center and Washington Streets to the Weather Bureau on August 6, 1895.

    In 1901 the office was moved to the southwest corner of 1st Avenue and Adams where it remained until it moved into the Federal Building on the southwest corner of 1st Avenue and Van Buren in March 1913. Three years later in June 1916, the office moved to the Water User's Building on the southeast corner of 2nd Avenue and Van Buren. It remained there until September 1924 when it moved to the Ellis Building at 2nd Avenue and Monroe. On October 21, 1936, it moved to the Federal Building at Central and Fillmore where it stayed until it was closed on october 22, 1953.

    Meanwhile, the development of air transportation and teletype communications in the 1920s and 1930s altered and redirected somewhat the purpose of the Weather Bureau as first defined by the law in 1890. This law provided for "the distribution of meteorological information in the interest of agriculture and commerce..." as one of the Weather Bureau's major functions. "Commerce" now included the mushrooming aviation industry -- and in 1940, to meet this partial change in emphasis, the Weather Bureau was transferred from the Department of Agriculture to the Department of Commerce where it remains today. In support of this new means of transportation, another Weather Bureau office was established at Sky Harbor Airport on May 2, 1933, and observations were taken there also until July 1935 when Department of Commerce radio operators took over the program. The Weather Bureau returned again to this station in January 1939 and has managed the station ever since that time.

    In July 1965 the Weather Bureau was incorporated as an integral part of the Environmental Science Services Administration (ESSA). In October 1970, the name was changed to the National Weather Service, and it became an integral part of the National Oceanic and Atmospheric Administration (NOAA).

    ELEVATIONS AT
    NATIONAL WEATHER SERVICE FORECAST OFFICE
    PHOENIX, ARIZONA


    LATITUDE 33 deg 26' North
    LONGITUDE 112 deg 01' West

    ELEVATION OF AIRPORT

    1128 Feet

    ELEVATION OF IVORY TIP OF BAROMETER

    1109.31

    ELEVATION OF STATION PRESSURE

    1107

    ELEVATION OF GROUND AT HYGROTHERMOMETER

    1110

    ELEVATION OF GROUND AT WIND VANE AND ANEMOMETER

    1110

    ELEVATION OF CLIMATOLOGICAL STATION

    1107

    ELEVATION OF GROUND AT OFFICE

    1106

    ELEVATION OF HYGROTHERMOMETER

    Above Ground, 5

    ELEVATION OF WIND VANE AND ANEMOMETER

    Above Ground, 33

    ELEVATION OF SUNSHINE SWITCH

    Above Ground, 7

    ELEVATION OF PYRANOMETER

    Above Ground, 6

    ELEVATION OF RAIN GAGE

    Above Ground, 5

     


    Acceleration of Gravity at Phoenix: 979.428 cm/sec2

    Boiling Point of Water at Phoenix: 210oF

    Temperature Conversion F to C (C = (F-32)*5/9)

    Precipitation Conversion I to M (M = I*2.54)

    Pressure conversion I to M (insert here)

    IV. TEMPERATURE

     

    NORMAL MAXIMUM, MINIMUM, AND MEAN BY MONTHS
    1961-1990

    Month

    MAXIMUM

    MINIMUM

    MEAN

    January

    65.9

    41.2

    53.6

    February

    70.7

    44.7

    57.7

    March

    75.5

    48.8

    62.2

    April

    84.5

    55.3

    69.9

    May

    93.6

    63.9

    78.8

    June

    103.5

    72.9

    88.2

    July

    105.9

    81.0

    93.5

    August

    103.7

    79.2

    91.5

    September

    98.3

    72.8

    85.6

    October

    88.1

    60.8

    74.5

    November

    74.9

    48.9

    61.9

    December

    66.2

    41.8

    54.1

    Annual

    85.9

    59.3

    72.6

    NORMAL MAXIMUM, MINIMUM, AND MEAN BY MONTHS
    1971-2000

    Month

    MAXIMUM

    MINIMUM

    MEAN

    January

    67.3

    44.8

    56.1

    February

    71.4

    48.4

    59.9

    March

    76.1

    53.0

    64.5

    April

    84.7

    57.6

    71.1

    May

    93.9

    67.4

    80.6

    June

    103.9

    75.6

    89.8

    July

    106.6

    82.9

    94.7

    August

    104.5

    81.6

    93.0

    September

    99.0

    75.6

    87.3

    October

    87.7

    62.1

    74.9

    November

    75.0

    50.4

    62.7

    December

    67.1

    43.9

    55.5

    Annual

    86.4

    61.9

    74.2

     


    HIGHEST MEAN AND LOWEST MEAN BY MONTHS AND YEAR OF OCCURRENCE 1896-2007

    Month

    HIGHEST

    YEAR

    LOWEST

    YEAR

    January

    62.0

    2003

    43.2

    1937

    February

    66.0

    1991

    48.6

    1939

    March

    72.3

    2004

    54.3

    1897

    April

    80.1

    1989

    62.4

    1967

    May

    87.0

    1984

    69.0

    1917

    June

    94.6

    2006

    79.0

    1965

    July

    97.7

    2003

    85.4

    1912

    August

    96.2

    2007

    84.6

    1918

    September

    92.2

    2001

    78.9

    1900, 1912

    October

    82.7

    2003

    66.2

    1916

    November

    70.0

    2007

    55.0

    1922

    December

    61.3

    1980

    46.6

    1911

    Annual

    77.0

    1989

    67.8

    1964


    HIGHEST AND LOWEST MEAN MAXIMUM AND HIGHEST AND LOWEST MEAN MINIMUM
    BY MONTHS AND YEAR OF OCCURRENCE - 1896-2008

     

    MEAN MAXIMUM

     

     

     

     

    MEAN MINIMUM

     

    HIGHEST

    YEAR

    LOWEST

    YEAR

     

    HIGHEST

    YEAR

    LOWEST

    YEAR

    January

    74.6

    2003

    53.5

    1949

     

    49.8

    1993

    31.9

    1937

    February

    78.7

    1991

    60.5

    1939

     

    53.2

    1991

    33.4

    1964

    March

    86.7

    1972

    67.3

    1897
    1958

     

    59.5

    2004

    40.3

    1917

    April

    94.2

    1989

    75.1

    1900

     

    65.9

    1989

    47.5

    1967

    May

    101.2

    1984

    83.7

    1917

     

    73.7

    1997

    54.2

    1917

    June

    108.6

    1974

    96.0

    1967

     

    81.8

    2006

    60.6

    1965

    July

    109.8

    1989

    97.7

    1912

     

    86.6

    2003

    73.1

    1912
    1913

    August

    107.3

    1962

    97.0

    1955

     

    86.1

    2007

    71.3

    1900

    September

    104.6

    2001

    93.6

    1900

     

    80.6

    1983

    63.6

    1912
    1965

    October

    95.8

    1952

    80.7

    1919

     

    70.8

    2003

    50.8

    1923

    November

    82.3

    1949

    67.4

    2000

     

    58.3

    2007

    37.3

    1916

    December

    74.9

    1980

    59.2

    1909

     

    48.2

    1977
    1991

    32.6

    1916

    Annual

    89.8

    1989

    81.4

    1913

     

    64.9

    2003

    53.1

    1917


    Greatest number of consecutive months with average temperature below normal:

    13 Months from May 1916 through May 1917

    Greatest number of consecutive months with average temperature above normal:

    38 Months from January 1988 through February 1991

     

    HIGHEST MAXIMUM AND LOWEST MINIMUM
    BY MONTHS AND DAY AND YEAR OF OCCURRENCE
    1896-2008

     

     

    HIGHEST

     

     

    LOWEST

     

    MAXIMUM

    DAY

    YEAR

    MINIMUM

    DAY

    YEAR

    January

    88

    19

    1971

    16

    7

    1913

    February

    92

    25
    27

    1921
    1986

    24

    7
    8

    1899
    1933

    March

    100

    26

    1988

    25

    4

    1966

    April

    105

    20
    29

    1989
    1992

    35

    10

    1922

    May

    114

    30

    1910

    39

    3

    1899

    June

    122

    26

    1990

    49

    4

    1908

    July

    121

    28

    1995

    63

    4
    5

    1912
    1912

    August

    116

    1
    4

    1972
    1975

    58

    20

    1917

    September

    116

    1

    1950

    47

    22
    20
    21

    1895
    1965
    1965

    October

    107

    1
    2

    1980
    1980

    34

    30

    1971

    November

    96

    1
    2

    1924
    1924

    27

    23

    1931

    December

    87

    10

    1950

    22

    31
    26

    1900
    1911

    Annual

    122

    JUN 26

    1990

    16

    JAN 7

    1913


    Temperature

    LOWEST MAXIMUM AND HIGHEST MINIMUM
    BY MONTHS AND DAY AND YEAR OF OCCURRENCE
    1896-2008

     

     

    LOWEST

     

     

     

    HIGHEST

     

    MAXIMUM

    DAY

    YEAR

     

    MINIMUM

    DAY

    YEAR

    January

    39

    6
    21

    1913
    1937

     

    61

    27

    1988

    February

    46

    6
    8

    1899
    1903

     

    65

    21

    1996

    March

    49

    2

    1915

     

    74

    28

    1986

    April

    52

    1

    1949

     

    77

    27

    1987

    May

    54

    1

    1915

     

    86

    29

    1983

    June

    68

    2

    1899

     

    93

    27

    1990

    July

    79

    1

    1911

     

    96

    15

    2003

    August

    73

    27

    1951

     

    95

    12

    2003

    September

    66

    23

    1895

     

    90

    3
    3

    1

    1982
    1983

    2007

    October

    56

    30

    1959

     

    83

    2

    1997

    November

    40

    28

    1919

     

    73

    4

    2001

    December

    36

    10

    1898

     

    65

    3

    1986

    Annual

    36

    DEC 10

    1898

     

    93

    JUN 27
    JUL 20

    1990
    1989

     

    GREATEST AND LEAST MONTHLY TEMPERATURE RANGE
    BY MONTHS AND YEAR OF OCCURRENCE
    1896-1995

     

     

    GREATEST

     

    LEAST

     

    RANGE

    YEAR

    RANGE

    YEAR

    January

    69

    1971

    33

    1995

    February

    61

    1921

    31

    1993

    March

    67

    1966

    35

    1980

    April

    62

    1949

    44

    1931

    May

    66

    1910

    40

    1981

    June

    63

    1929

    38

    1986

    July

    50

    1905

    33

    1959
    1981

    August

    51

    1918
    1962

    31

    1955

    September

    58

    1945

    35

    1981

    October

    66

    1917

    33

    1983

    November

    67

    1931

    38

    1986

    December

    58

    1911

    35

    1992

    Annual

    96

    1990

    77

    1984
    1991
    1992

     

    HOTTEST AND COOLEST SUMMERS 1896-1995
    (June, July, August, and September Combination)

     

    HOTTEST

    Year

    COOLEST

    Year

    93.4

    1981

    84.1

    1912

    93.3

    1989

    84.2

    1913

    92.7

    1988

    84.4

    1923

    92.1

    1994

    84.6

    1965

    92.0

    1977

    85.1

    1964

     

     

    HOTTEST THREE
    SUCCESSIVE MONTHS

     

     

    HOTTEST TWO
    SUCCESSIVE MONTHS

    Temp

    (Combination)

     

    Temp

    (Combination)

    94.8

    June, July, August 1981

     

    95.6

    July, August 1989

    94.4

    June, July, August 1988

     

    95.5

    July, August 1981

    94.4

    June, July, August 1989

     

    95.1

    July, August 1988

    93.9

    June, July, August 1985

     

    94.8

    July, August 1991

    93.8

    June, July, August 1994

     

    94.7

    July, August 1985

    93.5

    June, July, August 1977

     

    94.6

    July, August 1977

    93.2

    June, July, August 1986

     

    94.6
    94.6
    94.6

    July, August 1994
    July August 1995
    July, August 1995


    HOTTEST MONTH

    Temperature

    Month

    Year

    97.4

    July

    1989

    96.2

    July

    1988

    95.8

    August

    1981

    95.6

    July

    1980

    95.5

    July

    1983

    95.3

    August

    1994


    WARMEST AND COLDEST WINTERS 1896-FEBRUARY 1995
    (December, January, February Combination)

    WARMEST

    Year

     

    COLDEST

    Year

    60.6

    1980-1981

     

    49.3

    1963-1964

    59.4

    1985-1986

     

    49.8

    1948-1949

    58.6

    1991-1992

     

    50.0

    1916-1917

    58.5

    1990-1991

     

    52.2

    1945-1946

     

     

    COLDEST TWO
    SUCCESSIVE MONTHS

     

     

    COLDEST MONTH

    48.0

    January, February

    1964

     

    43.2

    January 1937

    48.2

    December, January

    1936-1937

     

    44.6

    January 1949

    48.3

    December, January

    1948-1949

     

    46.6

    December 1911

    48.4

    December, January

    1931-1932

     

    47.0

    January 1932

    48.7

    January, February

    1949

     

    47.1

    December 1916

     

    RECORD HIGH DEW POINTS IN DEGREES AND DATES OF OCCURRENCE
    1896-1995

     

    HIGHEST HOURLY DEW POINTS

     

    Dew Point (F)

    Month

    Day

    Year

    79

    July

    19

    1957

    78

    August

    9

    1977

    78

    August

    20

    1978

    77

    August

    1

    1951

    76

    July

    10

    1899

    76

    August

    10

    1913

    76

    August

    4

    1943

    76

    July

    31

    1945

    76

    July

    17

    1953

    76

    July

    22

    1966

    76

    August

    19

    1966

     

    HIGHEST DAILY AVERAGE DEW POINTS

     

    Dew Point (F)

    Month

    Day

    Year

    74

    August

    4

    1943

    73

    August

    19

    1966

     

    HIGHEST MONTHLY AVERAGE DEW POINTS

     

    Dew Point (F)

    Month

    Year

    68

    August

    1955

    67

    August

    1943

     

    RECORD LOW DEW POINTS IN DEGREES AND DATES OF OCCURRENCE


    1896-June 1995

    LOWEST HOURLY DEW POINTS

     

    Dew Point (F)

    Month

    Day

    Year

    -23

    November

    28

    1976

    -22

    December

    21

    1977

    -15

    January

    29

    1970

    -14

    February

    2

    1972

    -13

    Februrary

    3

    1972

    -13

    April

    13

    1974

    -12

    March

    10

    1977

    -11

    February

    4

    1972

     

    LOWEST DAILY AVERAGE DEW POINTS

     

    Dew Point (F)

    Month

    Day

    Year

    -10

    December

    21

    1977

    -5

    February

    3

    1972

     

    LOWEST MONTHLY AVERAGE DEW POINTS

     

    Dew Point (F)

    Month

    Year

    20

    February

    1972

    21

    March

    1977

     

    RECORD LOW HOURLY HUMIDITIES IN PERCENT AND DATES OF OCCURRENCE


    1896-June 1995

    Relative Humidity (%)

    Month

    Day

    Year

    2

    May

    8

    1904

    2

    May

    16

    1907

    2

    May

    13

    1976

    2

    December

    21

    1977

    2

    April

    21

    1979

    2

    June

    4

    1982

     

    HEAT INDEX
    (Apparent Temperature)



    Most people are familiar with the term "wind-chill factor" which gives the combined effects of wind and temperature as an equivalent calm air temperature. For example, if the temperature is 0_F and the wind is 5 mph, the wind-chill factor is -5_F; at 10 mph, it is -22_F; and at 20 mph it is -39_F. Just as an increase in wind makes the cold air more unbearable, so does an increase in the moisture content of the air make the high summer temperatures more uncomfortable.

    In most sections of the country, people look forward to summer. In the desert southwest, however, summer is the most undesirable time of the year. The term "Heat Index" is an apparent temperature based on the actual temperature and the amount of moisture in the air. The Heat Index Graph, devised by the National Weather Service, uses temperature and humidity values to determine the heat index. The areas of the graph are labeled: very warm, hot, very hot, and extremely hot. Most of the typical sunny summer days in the high country of Arizona fall into the very warm category. At the 5000-foot level, they fall into the hot, and in the lower deserts, they are in the very hot area of the graph. The chart also gives the heat syndrome for each classification.

    The dew point, or the temperature to which the air must be cooled before condensation can take place, gives a true value of now much moisture is actually in the air. By knowing the temperature and dew point, the humidity can be determined. Using the temperature and humidity, the heat index can be arrived at by using the graph.

    The prolonged summer head with maximum temperatures generally between 105 and 110 degrees in the Phoenix area causes some degree of fatigue in most people. Exhaustion and even heatstroke and sunstroke are possible with prolonged outdoor activity. This is especially true during much of July and August when the atmosphere becomes laden with tropical moisture.

    Phoenix records were checked back to 1896 to find the highest humidity ever for each temperature from 100 through 118 degrees.

     TEMPERATURE

    DEW POINT

    HUMIDITY

    HEAT INDEX

    100

    75

    45

    112

    101

    74

    43

    112

    102

    69

    35

    110

    103

    69

    34

    110

    104

    68

    32

    111

    105

    69

    32

    113

    106

    67

    29

    112

    107

    66

    27

    112

    108

    68

    28

    116

    109

    66

    26

    116

    110

    62

    22

    113

    111

    63

    22

    116

    112

    59

    18

    113

    113

    59

    18

    115

    114

    57

    16

    114

    115

    56

    15

    115

    116

    56

    15

    117

    117

    56

    14

    117

    118

    56

    14

    118


    It is interesting to note that with high moisture content, with humidities in the 30% and 40% range, the temperature never reached over 105 degrees. It is only with very dry air that temperatures climbed over 112 degrees. This is nature's way of not allowing conditions to get entirely out of hand.

    THE MYTH OF INCREASING MOISTURE LEVELS IN PHOENIX

    By Robert C. Balling, Jr., and Sandra W. Brazel
    Office of Climatology, Arizona State University



    Is Phoenix becoming more humid? Many local residents believe that irrigated landscaping, swimming pools, and lakes and canals in new housing developments around the city are forcing moisture levels noticeably upward. However, many scientists have shown that cities usually act to decrease moisture levels in the atmosphere. This is caused by (a) paved surfaces that store little moisture and force rapid runoff following a rain event and (b) increased temperature in the "urban heat island".

    Despite local interest in atmosphere moisture trends in the valley, surprisingly little scientific research has directly addressed this issue.

    We decided to examine the Phoenix, Arizona, weather records from 1896-1984 to see if there has been a change in the humidity of the Phoenix urban area. We chose relative humidity and dew point temperatures for statistical analysis. The dew point temperature is a better indicator of the amount of moisture in the air, which is the major contributor to human discomfort.

    Since Arizona has a distinct two season rainfall pattern (a monsoon season, July through September and a winter season, December through April), we chose the months of May, June, October, and November for analysis. These transition months should be the least affected by large-scale weather disturbances since they are in between the precipitation seasons. Thus any urban effect on humidity should be clearly evident.

    We chose six different relatively sophisticated statistical techniques to analyze the time series patterns in the atmospheric moisture data. These techniques basically search for "climatic signals" that may be contained in the "noisy" variance patterns in our data. These statistical procedures allow us to make conclusions regarding any trends, cycles, or discontinuities in the moisture records.

    The results for the dew points were somewhat surprising. In May, October, and November, our statistical procedures indicated that the variations in the data were random; however, some form of non-random variation appeared to exist in the June dew points. Our analyses showed that trend was not the source of non-random inter-annual variation in June (or any other month). The systematic variations in June were found to be related in several significant cycles in the data. One cycle showed a maximum occurring in 1943, and a minimum 1898. This important cycle shows that we are presently heading towards another minimum projected for 1987. Another cyclical pattern showed maxima in 1917 and 1962, and minima in 1939 and 1984. Clearly dew points are not rising in Phoenix.

    Given the steady or falling dew points, and assuming the highly probable occurrence of some urban heat island effects (higher temperatures in the city), the relative humidity values should display decreasing levels, again contrary to popular opinion. All of our statistics from each month indicated a strong downward trend in the relative humidity levels. The levels display a peak in the 1920s and a pronounced minimum in the 1970s and 1980s. So we have concluded that while increases in irrigated and sprinkled areas and open water surfaces may have occurred in the growing Phoenix area, many other effects of urbanization have apparently produced an overriding, counteracting impact on the atmospheric moisture levels.

    AVERAGE TEMPERATURE and RELATIVE HUMIDITY BY FIVE-YEAR PERIODS
    1896-1995

    5-Year Interval

    Temperature

    Relative Humidity

    1896-1900

    69.8

    38

    1901-1905

    70.1

    39

    1906-1910

    69.7

    44

    1911-1915

    68.9

    44

    1916-1920

    68.9

    48

    1921-1925

    70.2

    44

    1926-1930

    70.9

    41

    1931-1935

    71.8

    40

    1956-1960

    71.3

    40

    1936-1940

    71.9

    47

    1941-1945

    70.5

    41

    1946-1950

    71.3

    43

    1951-1955

    71.0

    41

    1961-1965

    69.6

    38

    1966-1970

    70.7

    40

    1971-1975

    71.8

    35

    1976-1980

    73.5

    46

    1981-1985

    74.3

    39

    1986-1990

    75.8

    34

    1991-1995

    74.6

    37

    These values of relative humidity are averages of the five years. The yearly averages are based on the averages of the twelve months. The monthly averages are based on daily values taken at 5 a.m. and 5 p.m.

    These data also show high values in the 1910s and 1920s and low values in the 1970s and 1980s. This is in good agreement with the above research project.

    It again points out that with urbanization, more buildings of all kinds, more paved surfaces and the heat island effect, the relative humidity decreases.

    CLIMATE OF PHOENIX: PART 2

    DAYS WITH 100 DEGREES OR HIGHER 1896-1995

    The date of the occurrence of the first 100 degree temperature in the spring and the last in the fall has always been of primary interest to the public.

    The average number of days per year with a maximum temperature of 100 degrees or higher is 89.4. These days are distributed throughout the year as follows:

    AprilMayJuneJulyAugustSeptemberOctober
    0.45.120.226.223.213.01.3

    The least number of such days was 48 in 1913.
    The greatest number of such days was 143 in 1989.

    The greatest number of consecutive days with maximum temperature of 100 degrees or higher was 76 from June 10 through August 24 1993.

    SPRING

    Earliest Date of First Occurrence of 100 or Higher: March 26, 1988

    Average Date of First Occurrence of 100 or Higher: May 14 (1961-1995 Average Date May 6)

    Latest Date of First Occurrence of 100 or Higher: June 18, 1913

    FALL

    Earliest Date of Last Occurrence of 100 or Higher: September 2, 1904

    Average Date of Last Occurrence of 100 or Higher: September 27 (1961-1995 Average Date September 29)

    Latest Date of Last Occurrence of 100 or Higher: October 20, 1921

    DAYS WITH 110 DEGREES OR HIGHER 1896-1995

    Most residents of Phoenix put up with temperatures below 110 without grumbling. However, when the mercury climbs to 110 or higher, even the old-timers feel the heat and begin to complain.

    The average number of days per year with a maximum temperature of 110 degrees or higher is 9.9. These days are distributed throughout the year as follows:

    MayJuneJulyAugustSeptember
    0.13.34.41.70.4

    The least number of such days was 0 in 1911.
    The greatest number of such days was 28 in 1979.

    The greatest number of consecutive days with maximum temperature of 110 degrees or higher was 18 from June 12 through June 29, 1974.

    SPRING

    Earliest Date of First Occurrence of 110 or Higher: May 8, 1989

    Average Date of First Occurrence of 110 or Higher: June 20 (1961-1995 Average Date June 14)

    Latest Date of First Occurrence of 110 or Higher: August 9, 1915

    FALL

    Earliest Date of Last Occurrence of 110 or Higher: June 5, 1912

    Average Date of Last occurrence of 110 or Higher: August 7 (1961-1995 Average Date August 17)

    Latest Date of Last Occurrence of 110 or Higher: September 12, 1971

    PROBABILITY IN PERCENT OF OBSERVING 100 OR HIGHER, 105 OR HIGHER AND 110 OR HIGHER 1896-1995

    PROBABILITY (Percent)FIRST OCCURRENCE IN SPRING LAST OCCURRENCE IN FALL
    100 OR Higher105 OR Higher110 OR Higher100 OR Higher105 OR Higher110 OR Higher
    90JUN 6JUN 21JUL 8SEP 12 AUG 20JUL 11
    80MAY 28JUN 17JUL 1SEP 18 AUG 23JUL 18
    70MAY 24JUN 13JUN 29SEP 21SEP 1JUL 26
    60MAY 19JUN 10JUN 27 SEP 24SEP 6AUG 1
    50MAY 14JUN 7JUN 19 SEP 27SEP 10AUG 7
    40MAY 13JUN 3JUN 20 SEP 28SEP 14AUG 10
    30MAY 10MAY 30JUN 15 SEP 30SEP 16AUG 19
    20MAY 6MAY 25JUN 11 OCT 5SEP 19AUG 26
    10APR 20MAY 16JUN 4 OCT 9SEP 23SEP 3

    Examples:

    There is a 40 percent probability that the first 100 degree temperature or higher will occur as early as May13.

    There is a 30 percent probability that the last 110 degree temperature or higher will occur as late as August19.

    The 50 percent level also gives the average date of the first occurrence in spring and the average date of the last occurrence in fall.

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 120 OR HIGHER
    1896-1995

    # of daysDateT of 1st DayT of 2nd Day
    2 daysJune 25-26, 1990120122
    1 dayJuly 28, 1995121

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 115 OR HIGHER
    1896-1995


    # of daysMonthdaysyearT of 1st dayT of 2nd dayT of 3rd dayT of 4th day
    4 daysJune19-221968115115115115
    4 daysJune25-281979115116116117
    4 daysJune25-281990120122118118
    4 daysJuly26-291995116118121115
    3 daysJuly 5-71905115116115
    3 daysJuly 9-111958116115118
    3 daysJune14-161974115115115
    3 daysJune24-261994116116116

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 110 OR HIGHER
    1896-1995

    # of daysStartEndYear
    18 daysJune 12June291974
    17 daysJuly 25August 101995
    10 daysJune 29July 81989
    9 daysJune 27July 51907
    9 daysJuly 3July 111940
    9 daysJune 17June 251978
    9 daysJune 18June 261981
    9 daysJune 20June 281990
    8 daysJune 11June 181896
    8 daysJuly 5July 121901
    8 daysJuly 7 July 141958
    8 daysJuly 13July 201978

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 105 OR HIGHER
    1896-1995

    # of daysStartEndYear
    28 daysJune 10July 71936
    27 daysJune 10July 61974
    25 daysJune 23July 171958
    23 daysJune 23July 151987
    22 daysJune 20July 111973

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 100 OR HIGHER
    1896-1995

    # of daysStartEndYear
    76 daysJune10-August 241993
    64 daysJune 7-August 91989
    61 daysJune 2-August 11935
    49 daysJune30-August 171966
    47 daysJune11-July 27 1951
    47 daysJune13-July 291988


    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 99 OR HIGHER
    1896-1995

    # of daysStartEndYear
    98 daysJuneSeptember 221973
    76 daysJune 10August 241993
    74 daysJune 29September 101978
    70 daysJune 1August 91989
    68 daysJune 11August 171966
    68 daysJune 7August 131980

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 75 OR LOWER
    1896-1995

    # of daysStartEnd
    120 daysNovember 16 1963March 14 1964
    107 daysNovember 27 1914March 13 1915
    105 daysNovember 11 1931February 23 1932


    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 60 OR LOWER
    1896-1995

    # of daysStartEndYear
    18 daysJanuary 10January 271898
    18 daysJanuary 17February 31933
    17 daysJanuary 23February 81949

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 55 OR LOWER
    1896-1995

    # of daysSequenceYear
    9 daysJanuary 17-251937
    9 daysJanuary 23-311949
    8 daysJanuary 20-271898
    8 daysFebruary 2-91903

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 50 OR LOWER
    1896-1995

    # of daysSequenceYear
    5 daysJanuary 20-241937
    5 daysDecember 13-171967
    5 daysJanuary 3-71971
    4 daysJanuary 11-141898
    4 daysFebruary 5-81903
    4 daysJanuary 4-71910
    4 daysJanuary 24-271949
    4 daysJanuary 31-February 31985

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 45 OR LOWER
    1896-1995

    # of daysStartEndYear
    3 daysJanuary 5January 71913
    3 daysJanuary 21January 231937
    2 daysJanuary 3January 41949

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MAXIMUM 42 OR LOWER
    1896-1995

    # of daysSequenceYearT of 1st dayT of 2nd dayT of 3rd day
    3 daysJanuary 5-71913423941

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 90 OR HIGHER
    1896-1995

    # of daysYear
    196 days1989
    192 days1934
    190 days1988
    188 days1990
    187 days1987
    186 days1972
    185 days1992
    180 days1974
    179 days1954
    178 days1950


    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 100 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    143 days 1989112 days 1991
    122 days 1988111 days 1975
    120 days 1992110 days 1958
    116 days 1973109 days 1979
    116 days 1978109 days 1984
    116 days 1987


    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 105 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    81 days 198970 days 1983
    75 days 197868 days 1977
    74 days 198868 days 1987
    73 days 197967 days 1933
    70 days 198167 days 1974

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 110 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    28 days 197925 days 1981
    27 days 193625 days 1995
    27 days 197424 days 1990
    27 days 198521 days 1983
    27 days 198920 days 1988
    25 days 197819 days 1940
    19 days 1973

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 115 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    7 days 1974 5 days 1994
    6 days 1989 4 days 1968
    5 days 1979 4 days 1995
    5 days 1985 3 days 1905
    5 days 1990 3 days 1934
    3 days 1958


    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 120 OR HIGHER
    1896-1995

    # of daysYear
    2 days1990
    1 day1995

    LEAST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 90 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    127 days1912137 days1941
    131 days1907137 days1957
    131 days1908138 days1896
    131 days1913139 days1899
    136 days1911141 days1903


    LEAST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 100 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    48 days191360 days1955
    53 days191262 days1908
    55 days190964 days1915
    59 days191165 days1907


    LEAST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 105 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    10 days191317 days1956
    12 days191119 days1912
    13 days191419 days1915
    15 days190920 days1923
    16 days195521 days1908


    LEAST NUMBER OF DAYS IN ONE YEAR WITH MAXIMUM 110 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    0 days19112 days1904
    1 day18972 days1906
    1 day19082 days1912
    1 day19092 days1914
    1 day19412 days1916
    1 day1956

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 35 OR LOWER
    1896-1995

    # of daysStartEndYear
    20 daysDecember 7December 261916
    17 daysJanuary 11January 271963
    17 daysDecember 25January 101967
    15 daysJanuary 14January 281937
    14 daysJanuary 19February 11904
    14 daysDecember 22January 41912
    14 daysDecember 23January 51954
    13 daysJanuary 6January 181964
    13 daysFebruary 8February 201966
    13 daysJanuary 3February 151971

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 32 OR LOWER
    1896-1995

    # of daysStartEndYear
    14 daysDecember 22January 41912
    14 daysDecember 8December 211916
    13 daysJanuary 14January 261898
    12 daysDecember 27January 71967
    11 daysJanuary 21January 311904
    11 daysJanuary 18January 281937
    10 daysJanuary 9January 181964

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 30 OR LOWER
    1896-1995

    # of daysStartEndYear
    12 daysDecember 8December 191916
    12 daysDecember 27January 71967
    11 daysDecember 24January 31896
    8 daysJanuary 21January 281937
    7 daysJanuary 12January 181963
    7 daysJanuary 4January 101971

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 28 OR LOWER
    1896-1995

    # of daysStartEndYear
    6 daysJanuary 4January 91971
    5 daysDecember 30January 31912
    5 daysJanuary 22January 261937
    5 daysJanuary 12January 161963

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 25 OR LOWER
    1896-1995

    # of daysStartEndYear
    4 daysJanuary 5January 81971
    4 daysJanuary 9January 121964
    3 daysJanuary 6January 81913
    3 daysJanuary 22January 241937
    3 daysJanuary 4January 61950
    3 daysJanuary 13January 151963

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 20 OR LOWER
    1896-1995

    # of daysDateT of 1st dayT of 2nd dayT of 3rd day
    3 daysJanuary 6-8, 1913171619
    2 daysJanuary 7-8, 19711920

    GREATEST NUMBER OF DAYS IN ONE WINTER WITH MINIMUM 32 OR LOWER
    1896-1995

    # of daysYears# of daysYears
    39 days1963-196421 days1965-1966
    30 days1897-189818 days1912-1913
    29 days1916-191716 days1936-1937
    24 days1911-191216 days1971-1972
    24 days1966-196714 days1968-1969
    21 days1903-190412 days1970-1971

    GREATEST NUMBER OF DAYS IN ONE WINTER WITH MINIMUM 28 OR LOWER
    1896-1995

    # of daysYears# of daysYears
    15 days 1963-19648 days 1966-1967
    10 days 1897-18987 days 1962-1963
    9 days 1911-19126 days 1903-1904
    9 days 1936-19376 days 1970-1971
    8 days 1916-19175 days 1912-1913

    GREATEST NUMBER OF DAYS IN ONE WINTER WITH MINIMUM 24 OR LOWER
    1896-1995

    # of daysYears# of daysYears
    5 days 1963-19643 days 1912-1913
    4 days 1897-18983 days 1936-1937
    4 days 1911-19123 days 1962-1963
    4 days 1970-19712 days 1916-1917

    GREATEST NUMBER OF DAYS IN ONE WINTER WITH MINIMUM 20 OR LOWER
    1896-1995

    # of daysYears# of daysYears
    3 days1912-19131 day1962-1963
    2 days1970-19711 day1963-1964

    LEAST NUMBER OF DAYS IN ONE WINTER WITH MINIMUM 32 OR LOWER
    1896-1995

    # of daysYears# of daysYears
    0 days 1977-19780 days 1993-1994
    0 days 1980-19810 days 1994-1995
    0 days 1981-19821 day 1937-1938
    0 days 1982-19831 day 1940-1941
    0 days 1983-19841 day 1942-1943
    0 days 1985-19861 day 1952-1953
    0 days 1991-1992
    0 days 1992-1993

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 85 OR HIGHER
    1896-1995

    # of daysStartEndYear
    14 daysAugust 18August 311981
    14 daysJuly 28August 101995
    11 daysJuly 18July 281981
    10 daysAugust 28September 61983
    10 daysJuly 5July 141985
    8 daysJuly 3July 101981
    8 daysJuly 31August 71986
    8 daysJune 22June 291988
    8 daysJune 24July 11990
    7 daysJuly 2July 81973
    7 daysJuly 28August 31977
    7 daysJuly 27August 21980
    7 daysAugust 24August 301985
    7 daysJuly 4July 101988
    7 daysJuly 14July 201989
    7 daysJune 27July 31994

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MINIMUM 80 OR HIGHER
    1896-1995

    # of daysStartEndYear
    40 daysJuly 7August 151977
    35 daysJune 15July 181988
    34 daysJuly 30September 11994
    28 daysJuly 16August 121980
    27 daysJuly 28August 231986
    26 daysAugust 24September 181983
    25 daysJuly 20August 131985
    22 daysJuly 18August 81983
    21 daysJuly 31August 201988
    20 daysAugust 16September 41981
    19 daysJuly 23August 101982
    18 daysJuly 2July191991
    17 daysJune 26July 121984
    17 daysJuly 29August 141989

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MINIMUM 85 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    51 days 198126 days 1986
    35 days 198323 days 1980
    33 days 197723 days 1985
    33 days 198919 days 1970
    32 days 199418 days 1969
    27 days 198217 days 1984
    27 days 199117 days 1992
    27 days 199515 days 1987

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MINIMUM 80 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    87 days198160 days1958
    76 days197760 days1970
    76 days198559 days1995
    71 days198357 days1982
    71 days198957 days1993
    70 days199454 days1969
    67 days198654 days1984
    66 days199152 days1933
    61 days199249 days1980

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH MEAN 100 OR HIGHER
    1896-1995

    #of daysDateDay 1Day 2Day 3Day 4Day 5Day 6Day7Day 8
    8 days August 3-10 1995:100 101 100 101 100101 101 102
    5 days July 4-8 1989:101 101 101 102 101
    5 days June 24-28 1990:100 104 107 106 103
    4 days July 29-August 1 1972: 102 100 101 103
    4 days July 2-5 1973:101 100 102 100
    4 days July 27-30 1995:101 103 102 101

    GREATEST NUMBER OF DAYS IN ONE YEAR WITH MEAN 100 OR HIGHER
    1896-1995

    # of daysYear# of daysYear
    14 days 19955 days 1973
    12 days 19895 days 1980
    10 days 19905 days 1985
    7 days 19855 days 1986
    7 days 19944 days 1970
    5 days 19694 days 1972

    HIGHEST DAILY MEAN
    1896-1995

    Mean TempDateMaximum TempMinimum Temp
    107June 26, 1990:12291
    106June 27, 1990:11893
    104June 25, 1990:12088

    LOWEST DAILY MEAN
    1896-1995

    TemperatureDateMaximum TempMinimum Temp
    28January 6 1913:3917
    28January 7 1913:4116
    33January 22 1937:4521
    33January 13 1963:4520
    33January 7 1971:4619

    GREATEST DAILY TEMPERATURE RANGE
    1896-1995

    Temp RangeDateMaximum TempMinimum Temp
    48June 13, 1917:10759
    48April 17, 1919:9648

    LEAST DAILY TEMPERATURE RANGE
    1896-1995

    Temp RangeDateMaximum TempMinimum Temp
    3December 10 1898:3633
    3November 26 1905:6057
    3October 24 1919:6259
    3February 3 1983:5249
    3November 25 1985:6158

    NORMAL AND HIGHEST AND LOWEST HEATING DEGREE DAYS BY MONTHS AND YEAR OF OCCURRENCE
    (Base 65 Degrees)


    NORMAL HIGHESTYEAR LOWESTYEAR
    1961-19901899-19951899-1995
    July 0 0 all 0 all
    August 0 0 all 0 all
    September 0 41965 0 most
    October 17 881908 0 several
    November 134 2931922 36 1989
    December 345 5731911 122 1980
    January 362 6811937 110 1986
    February 227 4581939 27 1991
    March 182 2881952 6 1934
    April 75 1331965 0 several
    May 8 551915 0 many
    June 0 0 all 0 all
    Season135020621916-1917 636 1980-1981

    A "heating degree day" is equal to 65 degrees Fahrenheit minus the average temperature for the day with negative differences being counted as zero. The heating degree day is used by utility companies to determine heating requirements. It is also used to help plan insulation protection and to determine the size of heating plants needed. Industry has found that a temperature of 72 degrees Fahrenheit is too high a base for these computations, since in every building there is a certain amount of heat generated by appliances, electric lights, human bodies, etc. The accumulation of "heating degree days" begins on July 1.

    Examples: If the average (mean) temperature for the day was 54, there would be 11 heating degree days for that day. If the average is 65 or higher, there would be 0 heating degree days for that day.

    NORMAL, HIGHEST, AND LOWEST COOLING DEGREE DAYS BY MONTHS AND YEAR OF OCCURRENCEL: (Base 65 Degrees)

    NORMAL HIGHESTYEAR LOWESTYEAR
    1961-19901969-19951969-1995
    January 8 10 19880most
    February 22 6119910several
    March 95 210198901973
    April 222 4591989421975
    May 436 68819842651971
    June 696 87319905821969
    July 884 101319898331976
    August 822 96119817631979
    September 618 78719835251985
    October 311 54319881511970
    November41124198841972
    December71319800most
    Annual41625245198936511971

    Cooling degree days on the base of 65 were first started nationally in 1969. Cooling degree days on the base of 80 have been used in Phoenix since 1951.

    A "cooling degree day" is equal to the average temperature for the day minus 65 degrees Fahrenheit with negative differences being counted as zero. The cooling degree day is used by utility companies to determine cooling requirements. It is also used to help plan insulation protection and to determine the size of refrigeration plants needed. The accumulation of "cooling degree days begins on January 1.

    Example: If the average (mean) temperature for the day was 94, there would be 29 cooling degree days for that day. If the average is 65 or lower, there would be 0 cooling degree days for that day.

    AVERAGE AND HIGHEST AND LOWEST COOLING DEGREE DAYS BY MONTHS AND YEAR OF OCCURRENCE
    (Base 80 Degree)

    AVERAGE HIGHESTYEAR LOWESTYEAR
    1961-19901951-19901951-1992
    January 0 0 all 0 all
    February 0 0 all 0 all
    March 0 71986 0most
    April 9 841989 0most
    May 71 2381984 31957
    June 264 4231990 411965
    July 423 5481989 2221955
    August 364 4961981 1831956
    September 189 3481983 651961 1964
    October 24 1501991 0several
    November 0 21988 0 most
    December 0 0 all 0 all
    Annual1344 19341989 7371964

    A "cooling degree day" is equal to the average temperature for the day minus 80 degrees Fahrenheit with negative differences being counted as zero. The cooling degree day is used by utility companies to determine cooling requirements. It is also used to help plan insulation protection and to determine the size of refrigeration plants needed. The accumulation of "cooling degree days" begins on January 1.
    Example: If the average (mean) temperature for the day was 94, there would be 14 cooling degree days for that day. If the average is 80 or lower, there would be 0 cooling degree days for that day.

    CLIMATE OF PHOENIX: PART 3


    NORMAL TOTAL AND MAXIMUM AND MINIMUM TOTAL BY MONTHS AND YEAR OF OCCURRENCE


    MonthNORMAL (1961-1990)MAXIMUM (1896-1995)YEARMINIMUM (1896-1995)YEAR
    January0.675.221993 0.001912 1924 1972
    February0.684.641905 0.001912 1967 1984
    March0.884.821941 0.001933 1956 1959 1984
    April0.223.361926 0.001904 1920 1948 1960 1962 1989 1991 1993
    May0.121.311930 0.001899 1911 1913 1932 1939 1942 1945 1946 1952 1974 1983 1988 1991
    June0.131.701972 0.001897 1900 1901 1908 1913 1916 1917 1923 1928 1935 1939 1942 1944 1945 1946 1947 1953 1963 1964 1968 1969 1970 1971 1974 1983 1985 1989
    July0.836.471911 trace1993 1995
    August0.965.331951trace1973 1975
    September0.865.411939 0.001953 1957 1968 1973 1988
    October0.654.401972 0.001898 1905 1909 1934 1950 1952 1973 1995
    November0.663.611905 0.001897 1903 1904 1912 1916 1917 1932 1937 1943 1945 1948 1956 1980
    December1.003.981967 0.001900 1901 1917 1958 1973 1981
    Annual7.6619.731905 2.821956

    Years in Which There Were 5 (the most) Calendar Months Without Measurable Precipitation:

    190419381945194819721973

    Years in Which All Twelve Calendar Months had Measurable Precipitation:

    192119251927194919651979198719901992

    DAILY NORMALS OF PRECIPITATION (1961-1990)

    DAYJAN TO NORMJAN TO DATEFEB TO NORMFEB TO DATEMAR TO NORMMAR TO DATEAPRTO NORMAPR TO DATEMAY TO NORMMAY TO DATEJUN TO NORMJUN TO DATE
    1.030.03.020.69.031.38.022.25.002.45.002.57
    2.030.06.020.71.031.41.022.27.002.45.002.57
    3.030.09.020.73.031.44.022.29.002.45.002.57
    4.030.12.020.75.031.47.022.31.002.45.002.57
    5.030.15.020.77.031.50.012.32.002.45.002.57
    6.020.17.020.79.031.53.012.33.002.45.002.57
    7.020.19.020.81.031.56.012.34.012.46.002.57
    8.020.21.020.83.031.59.012.35.012.47.002.57
    9.020.23.020.85.031.62.012.36.012.48.002.57
    10.020.25.020.87.031.65.012.37.012.49.002.57
    11.020.27.020.89.031.68.012.38.012.50.002.57
    12.020.29.020.91.031.71.012.39.012.51.002.57
    13.020.31.020.93.031.74.012.40.012.52.002.57
    14.020.33.020.95.031.77.012.41.012.53.002.57
    15.020.35.020.97.031.80.012.42.012.54.002.57
    16.020.37.020.99.031.83.012.43.012.55.002.57
    17.020.39.031.02.031.86.012.44.012.56.002.57
    18.020.41.031.05.031.89.012.45.012.57.002.57
    19.020.43.031.08.031.92.00 2.45.002.57.012.58
    20.020.45.031.11.031.95.002.45.002.57.012.59
    21.020.47.031.14.031.98.002.45.002.57.012.60
    22.020.49.031.17.032.01.002.45.002.57.012.61
    23.020.51.031.20.032.04.002.45.002.57.012.62
    24.020.53.031.23.032.07.002.45.002.57.012.63
    25.020.55.031.26.032.10.002.45.002.57.012.64
    26.020.57.031.29.032.13.002.45.002.57.012.65
    27.020.59.031.32.022.15.002.45.002.57.012.66
    28.020.61.031.35.022.17.002.45.002.57.012.67
    29.020.63.022.19.002.45.002.57.012.68
    30.020.65.022.21.002.45.002.57.022.70
    31.020.67.022.23.002.57
    Monthly Normal0.670.680.880.220.120.13
    DAYJAN TO NORMJAN TO DATEFEB TO NORMFEB TO DATEMAR TO NORMMAR TO DATEAPRTO NORMAPR TO DATEMAY TO NORMMAY TO DATEJUN TO NORMJUN TO DATE

    DAILY NORMALS OF PRECIPITATION (1961-1990)


    DAYJUL TO NORMJUL TO DATEAUG TO NORMAUG TO DATESEP TO NORMSEP TO DATEOCT TO NORM OCT TO DATENOV TO NORMNOV TO DATEDEC TO NORMDEC TO DATE
    1.022.72.043.57.034.52.035.38.026.02.036.69
    2.022.74.043.61.034.55.035.41.026.04.036.72
    3.022.76.043.65.034.58.035.44.026.06.036.75
    4.022.78.033.68.034.61.025.46.026.08.036.78
    5.022.80.033.71.034.64.025.48.026.10.036.81
    6.022.82.033.74.034.67.025.50.026.12.036.84
    7.022.84.033.77.034.70.025.52.026.14.036.87
    8.022.86.033.80.034.73.025.54.026.16.036.90
    9.022.88.033.83.034.76.025.56.026.18.036.93
    10.022.90.033.86.034.79.025.58.026.20.036.96
    11.032.93.033.89.034.82.025.60.026.22.036.99
    12.032.96.033.92.034.85.025.62.026.24.037.02
    13.032.99.033.95.034.88.035.64.026.26.047.06
    14.033.02.033.98.034.91.025.66.026.28.047.10
    15.033.05.034.01.034.94.025.68.026.30.047.14
    16.033.08.034.04.034.97.025.70.026.32.047.18
    17.033.11.034.07.035.00.025.72.026.34.047.22
    18.033.14.034.10.035.03.025.74.026.36.047.26
    19.033.17.034.13.035.06.025.76.026.38.047.30
    20.033.20.034.16.035.09.025.78.026.40.037.33
    21.033.23.034.19.035.12.025.80.026.42.037.36
    22.033.26.034.22.035.15.025.82.026.44.037.39
    23.033.29.034.25.035.18.025.84.026.46.037.42
    24.033.32.034.28.03 5.21.025.86.026.48.037.45
    25.033.35.034.31.035.24.025.88.036.51.037.48
    26.033.38.034.34.035.27.025.90.036.54.037.51
    27.033.41.034.37.025.29.025.92.036.57.037.54
    28.033.44.034.40.025.31.025.94.036.60.037.57
    29.033.47.034.43.025.33.025.96.036.63.037.60
    30.033.50.034.46.025.35.025.98.036.66.037.63
    31.033.53.034.49.026.00.037.66
    Monthly Normal0.830.960.860.650.661.00
    DAYJUL TO NORMJUL TO DATEAUG TO NORMAUG TO DATESEP TO NORMSEP TO DATEOCT TO NORM OCT TO DATENOV TO NORMNOV TO DATEDEC TO NORMDEC TO DATE

    GREATEST NUMBER OF DAYS WITH TRACE OR MORE AND 0.01 INCHES OR MORE BY MONTHS AND YEAR OF OCCURRENCE AND AVERAGE NUMBER OF DAYS WITH 0.01 INCHES OR MORE BY MONTHS


    1896-19951896-19951940-1995
    TRACE OR MOREYEAR0.01 OR MOREYEARAVERAGE 0.01 OR MORE
    January1619931419934.1
    February1719051419054.0
    March1619051219053.8
    April1819261319261.7
    May121992719921.0
    June81925 1931 1972 41899 1932 0.7
    July1819841318964.2
    August181963111913 19294.8
    September161897919392.9
    October121907 197291907 19722.7
    November1319131119052.5
    December141965111914 1923 1926 19654.0
    Annual106190574190536.4
    Least Annual371953181953


    Arizona Indian Proverb: "The south rain brings with it the beautiful odors of the land of everlasting summer and brightens the leaves of growing things".

    GREATEST NUMBER OF DAYS WITH 0.10 INCHES OR MORE, 0.50 INCHES OR MORE,
    AND 1.00 INCH OR MORE BY MONTHS AND YEAR OF OCCURRENCE (1896-1995)


    0.10 or moreYEAR0.50 or moreYEAR1.00 or moreYEAR
    January1119934199321905
    February919056190511908 1987
    March61905 19525194131941
    April619523190511926 1941
    May4199211930 1944 1976 19790
    June21967 197211955 1965 197211972
    July718964195531955
    August719635195121943 1995
    September8193931939 198421903 1939 1946 1984
    October51957 19744197211911 1914 1932 1957 1959 1963 1972 1988 1991 1993
    November9190531931 198211902 1905 1918 1919 1923 1931 1941 1993 1995
    December919145195911896 1898 1902 1915 1926 1948 1926 1940 1967 1978 1984 1987 1992
    Annual43190518190551941 1946 1984
    Least91904019530Many Years

    Arizona Indian Proverb: "When the clouds hang on the mountain side after a rain and the sun shines on the top of the mountain, the storm is over".

    MAXIMUM AMOUNTS FOR 5, 10, 15, AND 30 MINUTES; 1, 2, AND 24 HOURS BY MONTHS AND DAY AND YEAR OF OCCURRENCE 1896-1995

    5 Minutes 10 Minutes15 Minutes30 Minutes1 Hour2 Hours24 Hours
    January0.350.440.560.670.750.911.84
    3/19263/19263/19263/19263/192611/199310-11/1993
    February0.300.410.430.440.500.671.69
    6/193510/196310/196310/196312/19366/19355-6/1935
    March0.260.410.430.460.610.772.04
    4/19414/19414/194112/194112/19414/1941, 3/19832-3/1983
    April0.320.610.750.760.760.921.66
    19/195119/195119/195119/195119/19518/19265-6/1926
    May0.350.450.530.590.600.611.12
    20/197920/197920/197920/197920/197920/19794-5/1930
    June0.300.400.520.620.921.201.64
    12/195522/197222/197222/197222/197222/197221-22/1972
    July0.500.700.911.151.301.474.98
    24/197826/195226/195217/190826/19172/19111-2/1911
    August0.901.141.171.231.721.812.72
    16/198316/198316/198320/197818/19666/191827-28/1951
    September0.681.001.141.271.412.203.06
    16/196916/196916/196916/19694/19394/19393-4/1939
    October0.680.720.720.860.931.032.32
    1/19811/19811/198130/192830-31/192830-31/192814/1988
    November0.360.380.400.540.670.752.40
    10/193110/1931 23/191923/191914/191814/191827/19199-10/1923
    December0.130.220.280.380.520.681.92
    13/197519/196713/197519/19677/198619/196730-31/1915
    Annual0.901.141.171.271.722.204.98
    16 AUG 198316 AUG 198316 AUG 198316 SEP 196918 AUG 19664 SEP 19391-2 JUL 1911

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH TRACE OR MORE, 1896-1995

    14 daysJanuary 5-181993total5.12
    10 daysJuly22-311921total0.38
    10 daysDecember 3-121926total2.50
    9 daysJanuary 9-171897total3.59
    9 daysDecember12-201967total3.98
    9 daysFebruary13-211980total2.09
    9 daysJuly10-181984total0.49

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 0.01 INCHES OR MORE, 1896-1995

    10 daysDecember 3-121926total2.50
    9 daysFebruary13-211980total2.09
    9 daysJanuary10-181993total3.11
    8 daysJanuary 9-161897total3.59
    7 daysJanuary15-211917total1.62
    7 daysDecember13-191967total3.98

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 0.25 INCHES OR MORE, 1896-1995

    4 daysFebruary12-151931total2.83
    4 daysDecember12-151932total1.69

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 0.50 INCHES OR MORE, 1896-1995

    3 daysFebruary12-141931total2.48
    3 daysFebruary 5-71935total2.48
    3 daysMarch12-141941total2.67
    3 daysAugust27-291951total3.77

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 1.00 INCH OR MORE, 1896-1995


    2 daysJanuary 9-101905total2.69
    2 daysJuly 1-21911total5.49
    2 daysJuly25-261936total2.35
    2 daysJuly17-181946total2.31
    2 daysSeptember17-181946total2.65
    2 daysJuly24-251955total2.05

    Arizona Indian Proverb: "When the sun is in his house (in a halo or circle), it will rain soon".

    GREATEST NUMBER OF CONSECUTIVE DAYS WITHOUT TRACE OR MORE, 1896-1995


    91 daysJanuary 6 1984-April 51984
    88 daysOctober17 1917-January 121918
    88 daysApril10 1945-July 61945
    79 daysOctober 7 1916-December 241916
    77 daysApril23 1913-July 81913
    74 daysMarch29 1991-June 101991
    72 daysApril26 1974-July 61974

    GREATEST NUMBER OF CONSECUTIVE DAYS WITHOUT 0.01 INCHES OR MORE, 1896-1995

    160 daysDecember 30 1971-June 6 1972
    143 daysMarch 2 1960-July 22 1960
    125 daysJuly 16 1973-November 17 1973
    119 daysMarch 24 1904-July 20 1904
    118 daysFebruary 4 1899-June 1 1899
    117 daysMarch 11 1970-July 5 1970
    117 daysMarch 27 1989-July 21 1989
    114 daysMarch 11 1968-July 2 1968
    114 daysMarch 28 1991-July 19 1991
    105 daysSeptember 1 1938-December 14 1938
    105 daysMarch 24 1945-July 6 1945
    104 daysOctober 1 1917-January 12 1918
    102 daysApril 6 1909-July 16 1909

    AMOUNTS AND DATES OF ALL SNOWFALLS, 1896-1995

    AMOUNT
    1.0 inchJanuary 20 1933
    1.0 inchJanuary 20-21 1937*
    0.5 inchesFebruary 2 1939
    0.4 inchesDecember 21-22 1990
    0.2 inchesMarch 12 1917
    0.1 inchesNovember 28 1919
    0.1 inchesDecember 11 1985
    *(1 to 4 inches fell in parts of the city and remained in shaded areas until the 23 and 24)

    SNOWFALL: TRACE

    December 9 1898February 1 1939December 25 1974
    December 10 1898February 8 1939March 3 1976
    January 20 1904February 9 1939February 2 1985
    December 5 1909April 1 1949February 3 1985
    December 25 1911January 12 1951February 4 1985
    May 1 1915January 13 1962January 15 1987
    December 25 1916January 17 1962March 21 1991
    February 18 1918December 13 1967March 27 1991
    May 9 1930December 20 1968February 4 1994

    DAILY FREQUENCY OF OCCURRENCE OF TRACE OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    117252724146214731241315
    219263419167244833221217
    3252136171111214826181021
    4162531171412184827191124
    523232811136204229171121
    624351317711283727151222
    71933171587334525131714
    8223219199630422391822
    921352220148264618131725
    1028243111131036493191427
    1127282616147344525171419
    122428281797364725162030
    1327212418711333926141519
    142819231195384421141921
    152028191785513913202217
    1627261514124504317132322
    1727191615149484319121818
    1820162216129354125142118
    193129239117403917191022
    202727236138383218141224
    2123292618712543113141523
    221918231989484028131822
    2322172610108524618142120
    242119221089474221192213
    252622241281052361871723
    262127291471051402061622
    272925182379492619151527
    2827152517918413217161728
    2924820161118494217191526
    30201310815542920161321
    311813942311319
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation has fallen on 23 percent of the Christmas Days during the 95-year period from 1896 through 1995.

    DAILY FREQUENCY OF OCCURRENCE OF 0.01 INCHES OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    111181814615261714117
    2102025105411241713611
    320182755710301615413
    41018217647241015418
    51913169608222113715
    61520894310231410611
    71324765415211281011
    813271763211211031213
    912241565210264101016
    1018192247311181461320
    11241914114015221761114
    12162020115411271471017
    1320141152411171861014
    14171315351132015101311
    1513201274322226111413
    1619171284122165111115
    172214126352820871216
    18151212753172014111315
    19142487541517106717
    20141615553241597817
    2114221492522161091119
    22101316164526231481416
    2316101441324231591513
    2412131553130161091211
    2516171711222161061315
    261216195132821115918
    271712131421181811101216
    282061415352415791518
    29188121054262310131021
    301865162516131478
    31108118121115
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation of 0.01 inches or more has fallen on 15 percent of the Christmas Days during the 100-year period from 1896 through 1995.

    DAILY FREQUENCY OF OCCURRENCE OF 0.10 INCHES OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    1581073041210752
    261016413598456
    3119131011184716
    4610945131146111
    51056540312129410
    6121246115116537
    76122130697346
    86911412568366
    9511643011134710
    101216121314742813
    11141198108136258
    1261012433412115911
    13159710045122510
    144127130965679
    1510129510101202912
    1684950011105798
    1711355031395578
    1812553011199968
    1947652161145411
    20948150985266
    2179541312754812
    2245791310953109
    234583119976126
    2457422114106175
    25119810215763511
    265612110121163511
    276788009108478
    286679219757911
    29111540011146758
    301011031114966
    3166196610
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation of 0.10 inches or more has fallen on 11 percent of the Christmas Days during the 100-year period from 1896 through 1995.

    DAILY FREQUENCY OF OCCURRENCE OF 0.25 INCHES OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    1059210246532
    2349110542234
    39581010101513
    4466130041323
    54463100116425
    6661400363333
    7481000555134
    8222100334135
    9255330063329
    10887131312188
    11866500553245
    12368101485154
    13645000149048
    14165100342535
    15575100650248
    16616400961431
    178143001034146
    18730001756637
    19151100442437
    20633120554213
    21351211851248
    22114401422344
    231043013632102
    24351011976044
    255221011042056
    26237000666356
    27446100667245
    285466115655410
    29814000586444
    3060000504654
    312303317
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation of 0.25 inches or more have fallen on 6 percent of the Christmas Days during the 100-year period from 1896 through 1995.

    DAILY FREQUENCY OF OCCURRENCE OF 0.50 INCHES OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    1004000132220
    2003000311100
    3522100040202
    4333020011211
    5022200073112
    6220100020201
    7210000122002
    8010100112102
    9113000002214
    10413110001144
    11312300001034
    12132001224021
    13122000104024
    14131000022121
    15222000320223
    16213100221010
    17301000413011
    18110000214324
    19111100210213
    20211010220010
    21120000321021
    22001101110011
    23000201012241
    24130000532013
    25412000420012
    26023000333021
    27112000423212
    28213100134214
    29200000123021
    3020000100412
    311002213
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation of 0.50 inches or more have fallen on 2 percent of the Christmas Days during the 100-year period from 1896 through 1995.

    DAILY FREQUENCY OF OCCURRENCE OF 1.00 INCH OR MORE IN PERCENT, 1896-1995

    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    1000000121010
    2000000111000
    3011000010100
    4001000001000
    5000100021000
    6000000010100
    7000000000001
    8100000002101
    9100000000000
    10100000001011
    11100100001010
    12101000102010
    13000000002001
    14001000021121
    15000000010000
    16101000111000
    17100000202001
    18000000111001
    19000000000200
    20000000110010
    21000000100000
    22000001100000
    23000000000000
    24010000210000
    25000000300000
    26001000302010
    27000000111211
    28000000101000
    29100000101000
    3010000100102
    310000010
    DAYJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
    For Example: Precipitation of 1.00 inch or more has fallen on 2 percent of the August 1st's during the 100-year period from 1896 through 1995.

    FREQUENCY OF OCCURRENCE OF 0.01 INCHES OR MORE OF PRECIPITATION ON CONSECUTIVE DAYS IN PERCENT BY MONTHS, 1896-1995

    ANY ONE DAY2ND DAY3RD DAY4TH DAY5TH DAY6TH DAY7TH DAY8TH DAY
    January15.43.21.10.40.20.10.10.1
    February17.13.91.50.50.30.1 * *
    March14.73.21.20.40.2 *0.0 0.0
    April 7.71.60.30.1 *0.00.00.0
    May 3.80.60.10.00.00.00.00.0
    June 3.10.5 *0.00.00.00.00.0
    July17.42.90.70.30.10.10.00.0
    August20.33.20.90.3 *0.00.00.0
    September12.12.20.70.20.1 *0.00.0
    October 9.41.80.50.10.00.00.00.0
    November10.02.50.70.1 * 0.00.00.0
    December 14.62.81.00.20.10.10.1 *

    * Less than .05 percent

    Example:In January, on the average, there was a 15.4 percent frequency of occurrence of 0.01 inches or more of precipitation on any day. For a 2-day period there was a 3.2 percent, for a 3-day period 1.1 percent, for a 4-day period 0.4 percent, for a 5-day period 0.2 percent, for a 6-day period, a 7-day period, and 8-day period 0.1 percent.

    Arizona Indian Proverb: "When the sun sets unhappily (with a hazy veiled face) then will the morning be angry with wind, storm, and sand".

    "The moon her face if red be, of water she speaks".
    WXPART4

    ESTIMATED RETURN PERIODS FOR SHORT-DURATION PRECIPITATION (Inches)
    RETURN PERIOD (YEARS)

    Rainfall Duration

    1

    2

    5

    10

    25

    50

    100

    5 Minutes

    0.17

    0.26

    0.38

    0.47

    0.59

    0.68

    0.77

    10 Minutes

    0.27

    0.40

    0.59

    0.72

    0.91

    1.06

    1.20

    15 Minutes

    0.34

    0.50

    0.74

    0.92

    1.15

    1.34

    1.52

    30 Minutes

    0.47

    0.70

    1.03

    1.27

    1.60

    1.86

    2.10

    1 Hour

    0.60

    0.88

    1.30

    1.61

    2.02

    2.35

    2.66

    2 Hours

    0.65

    0.94

    1.39

    1.72

    2.15

    2.49

    2.82

    3 Hours

    0.69

    1.01

    1.48

    1.82

    2.27

    2.62

    2.97

    6 Hours

    0.81

    1.16

    1.70

    2.07

    2.57

    2.96

    3.35

    12 Hours

    0.91

    1.30

    1.90

    2.30

    2.84

    3.26

    3.69

    24 Hours

    1.02

    1.44

    2.10

    2.53

    3.12

    3.57

    4.04

    Examples: This means that 0.74 inches of rain can be expected in 15 minutes once every 5 years.
    This means that 0.60 inches of rain can be expected in 1 hour once every year.
    This means that 2.57 inches of rain can be expected in 6 hours once every 25 years.


    Source: ESTIMATED RETURN PERIODS FOR SHORT DURATION PRECIPITATION IN ARIZONA, Technical Memorandum WBTM WR-44, October 1969.

    THUNDERSTORMS, HAIL, AND TORNADOES
    ARIZONA MONSOON

    The so-called "Arizona Monsoon" is a marginal summer type monsoon, not nearly as intense as those in other places of the globe. Some people insist that it should not be called "monsoon" but rather a period of summer thunderstorm activity. It is, however, a seasonal change in the wind direction from a westerly to a southerly wind during July, August, and early September.

    It is not always a sustained period because there may be periods of hot, dry weather interspersed with the hot, humid days. The monsoon feature is most pronounced over the southern and central sections of the state and becomes more marginal over the northern part. The monsoon onset is often dramatic and occurs when the very hot, dry air is replaced by a surge of moist, tropical air. The source of the moisture is the Gulf of Mexico, the Gulf of California, and the Pacific Ocean off the west coast of Mexico.

    The Monsoon moisture, combined with the intense solar heating, creates uncomfortable heat and humidity and produces an abundance of thunderstorms. These thunderstorms at times are very intense and may cause very heavy rain with flash flooding and destructive winds and blowing dust with visibility near zero.

    For statistical purposes, a monsoon day has been defined as a day with average dew points of 55 degrees or higher. This figure represents a relatively high moisture value and is easily measured.

    Monsoon Statistics: 1896-1995

    Average Date of Monsoon Onset

    July 7

    Earliest Date of Onset

    June 16 1925

    Latest Date of Onset

    July 25 1987

    In Two Out of Three Years, Onset is between

    July 1 & July 16

    Average Date of First Break

    August 16

    Average Data of Ending

    September 13

    Monsoon Statistics: 1948-1995

    Average Total Number of Monsoon Days

    56 days

    Greatest Number of Monsoon Days

    99 in 1984; 86 in 1983

    Least Number of Monsoon Days

    27 in 1962; 28 in 1987

    Greatest number of consecutive monsoon days was 72, from June 25 through September 4, 1984. This was also the greatest number of consecutive days with dew point of 60 degrees or higher.

    Arizona Indian Proverb:"Rain will occur about a week after locusts begin to sing at night".

    Monsoon Start & End Dates: 1948-1995

    YEAR

    BEGAN

    ENDED

    # OF MONSOON DAYS

    TOTAL RAIN (JUL-AUG-SEP)

    1948

    Jul 17

    Sep 1

    40

    1.04

    1949

    Jul 1

    Sep 21

    60

    1.66

    1950

    Jul 4

    Sep 8

    40

    2.25

    1951

    Jul 11

    Sep 17

    65

    6.98

    1952

    Jul 3

    Sep 24

    66

    2.93

    1953

    Jul 4

    Aug 31

    54

    1.27

    1954

    Jun 23

    Sep 13

    76

    1.35

    1955

    Jul 11

    Sep 18

    59

    5.99

    1956

    Jul 10

    Aug 27

    37

    1.40

    1957

    Jul 3

    Aug 30

    57

    1.57

    1958

    Jun 19

    Sep 13

    68

    3.28

    1959

    Jun 28

    Sep 15

    74

    1.85

    1960

    Jul 21

    Sep 16

    54

    1.19

    1961

    Jul 2

    Sep 18

    74

    2.73

    1962

    Jun 27

    Aug 22

    27

    0.71

    1963

    Jul 19

    Sep 6

    44

    2.71

    1964

    Jul 7

    Sep 15

    60

    3.69

    1965

    Jul 9

    Sep 19

    60

    0.94

    1966

    Jun 27

    Oct 8

    65

    4.26

    1967

    Jul 3

    Sep 13

    67

    1.14

    1968

    Jul 3

    Sep 3

    43

    2.29

    1969

    Jul 11

    Sep 19

    67

    2.53

    YEAR

    BEGAN

    ENDED

    # OF MONSOON DAYS

    TOTAL RAIN (JUL-AUG-SEP)

    1970

    Jul 17

    Sep 13

    51

    4.35

    1971

    Jul 13

    Sep 10

    55

    2.15

    1972

    Jul 13

    Sep 10

    43

    2.20

    1973

    Jul 3

    Aug 22

    36

    1.30

    1974

    Jul 14

    Sep 28

    47

    3.06

    1975

    Jul 3

    Sep 19

    58

    1.20

    1976

    Jul 9

    Sep 28

    47

    3.29

    1977

    Jul 1

    Oct 10

    77

    2.01

    1978

    Jul 9

    Sep 9

    49

    3.23

    1979

    Jul 17

    Aug 19

    30

    1.61

    1980

    Jul 19

    Sep 7

    39

    0.75

    1981

    Jul 6

    Sep 24

    68

    1.43

    1982

    Jul 6

    Sept 26

    71

    2.52

    1983

    Jul 7

    Oct 10

    86

    5.29

    1984

    Jun 25

    Oct 5

    99

    9.38

    1985

    Jul 9

    Sep 2

    39

    2.79

    1986

    Jun 29

    Sep 3

    56

    2.93

    1987

    Jul 25

    Sep 5

    28

    2.10

    1988

    Jul 7

    Sep 2

    47

    1.50

    1989

    Jul 8

    Sep 6

    45

    1.71

    1990

    Jun 29

    Sep 25

    77

    4.86

    1991

    Jul 4

    Sep 10

    36

    1.07

    1992

    Jul 6

    Sep 22

    60

    4.28

    1993

    Jul 1

    Sep 13

    41

    0.61

    1994

    Jul 17

    Sep 13

    54

    2.01

    1995

    Jul 11

    Sep 18

    51

    4.58

    YEAR

    BEGAN

    ENDED

    # OF MONSOON DAYS

    TOTAL RAIN (JUL-AUG-SEP)

    WETTEST AND DRIEST MONSOON: 1896-1995

     

    YEAR

    JULY

    AUGUST

    SEPTEMBER

    TOTAL

    DRIEST

    1924

    0.09

    0.14

    0.12

    0.35

     

    1914

    0.21

    0.30

    Trace

    0.51

     

    1932

    0.11

    0.10

    0.34

    0.55

     

    1993

    Trace

    0.55

    0.06

    0.61

     

    1962

    0.10

    0.25

    0.39

    0.74

    WETTEST

    1984

    5.15

    0.87

    3.36

    9.38

     

    1911

    6.47

    1.68

    1.16

    9.31

     

    1946

    2.56

    2.01

    2.88

    7.45

     

    1896

    4.25

    1.77

    1.18

    7.20

     

    1951

    1.30

    5.33

    0.35

    6.98



    AVERAGE NUMBER OF DAYS WITH THUNDERSTORMS AND AVERAGE NUMBER OF DAYS WITH HAIL BY MONTHS: 1896-1995

    Month

    THUNDERSTORMS

    HAIL

    January

    0.3

    0.1

    February

    0.7

    0.2

    March

    0.9

    0.2

    April

    0.9

    0.1

    May

    1.1

    0.1

    June

    1.2

    *

    July

    6.6

    *

    August

    7.9

    *

    September

    3.5

    0.1

    October

    1.2

    0.1

    November

    0.6

    *

    December

    0.4

    0.1

    Annual

    25.4

    1.0

    *Less than .05



    GREATEST NUMBER OF DAYS WITH THUNDERSTORMS AND GREATEST NUMBER OF DAYS WITH HAIL BY MONTHS AND YEAR OF OCCURRENCE: 1896-1995

    Month

    Thunderstorms

    Hail

     

    Number of storms

    YEAR

    Number

    YEAR

    January

    3

    1982

    2

    1945 1949

    February

    5

    1931

    2

    1942

    March

    7

    1905

    2

    1912 1941 1952 1973

    April

    12

    1926

    1

    1908 1915 1926 1933 1940 1941 1942 1944 1951 1976 1988

    May

    8

    1992

    1

    1907 1920 1926 1930 1973 1992

    June

    6

    1972

    1

    1955 1965 1972

    July

    16

    1908 1917 1984

    1

    1915 1940 1970 1984

    August

    20

    1909

    1

    1905 1928 1942

    September

    13

    1897

    1

    1903 1935 1950 1964 1984

    October

    4

    1912 1928

    2

    1981

    November

    4

    1959

    1

    1898 1905 1984

    December

    4

    1940 1965

    1

    1921 1923 1926 1928 19 49 1964

    Annual

    48

    1905

    5

    1926


    FREQUENCY OF THUNDERSTORM OCCURRENCE IN PERCENT BY DAYS: 1896-1995

    DAY

    JUN

    JUL

    AUG

    SEP

    OCT

    1

    1

    10

    30

    18

    7

    5

    2

    14

    29

    16

    5

    10

    3

    20

    28

    13

    4

    15

    5

    26

    26

    10

    3

    20

    6

    30

    23

    8

    2

    25

    8

    32

    20

    7

    2

    Arizona Indian Proverbs: "The clouds must look like many sheep before the rains will come." "When the clouds rise in terraces of white, soon will the country of the corn priests be pierced with arrows of rain."

    LIGHTNING

    It is estimated that some 1800 thunderstorms are in progress over the earth's surface at any given time and that lightning strikes the earth 100 times each second.

    The average annual death toll for lightning is greater than for tornadoes or hurricanes. In 1984, 3 people were injured by lightning and 5 killed in Arizona. For the U.S., the figures were: 253 injuries and 67 fatalities. For the period 1959-1984, there were 71 injuries and 41 deaths in Arizona, and 6472 injuries and 2574 deaths nationally.

    Lightning is a secondary effect of electrification within a thunderstorm cloud system. Updrafts of warm moist air rising into cold air can cause small cumulus clouds to grow into large cumulonimbus cloud systems and on into thunderstorms. The transition from a small cloud to a turbulent electrified giant can occur in as little as 30 minutes.

    As a thunderstorm cumulonimbus develops, interactions of charged particles, external and internal electrical fields, and complex energy exchanges produce a large electrical field within the cloud. The distribution of electricity in a thunderstorm cloud is usually a concentration of positive charge in the frozen upper layers, and a large negative charge around a positive area in the lower portions of the cloud.

    PROTECT YOURSELF

    When a thunderstorm threatens, get inside a home or large building, or inside an all metal (not convertible) vehicle.

    Inside a home, avoid using the telephone, except for emergencies.

    If outside with no time to reach a safe building or an automobile, follow these rules:

    Do not stand underneath a natural lightning rod such as a tall, isolated tree in an open area.

    Avoid projecting above the surrounding landscape, as you would do if you were standing on a hilltop, in an open field, on the beach, or fishing from a small boat.

    Get out of and away from open water.

    Get away from tractors and other metal farm equipment.

    Get off of and away from motorcycles, scooters, golf carts, and bicycles. Put down golf clubs.

    Stay away from wire fences, clotheslines, metal pipes, rails, and other metallic paths which would carry lightning to you from some distance away.

    Avoid standing in small isolated sheds or other small structures in open areas.

    In a forest, seek shelter in a low area under a thick growth of small trees. In open areas, go to a low place such as a ravine or valley. Be alert for flash floods.

    If you are hopelessly isolated in a level field or prairie and you feel your hair stand on end, drop to your knees and bend forward putting your hands on your knees. Do not lie flat on the ground.

    (These are from the National Weather Service Lightning Safety).

    DESCRIPTION OF KNOWN TORNADOES AND FUNNEL CLOUDS IN THE GREATER PHOENIX AREA: 1955-1990

    June 13, 1955

    Severe thunderstorms were widespread over much of the eastern two-thirds of the state throughout the day. About 10:00 a.m., several funnel clouds were observed underneath one main cloud north of the White Tank Mountains. Later the same day (about 4:30 p.m.) possible tornado damage occurred east of Queen Creek Village; damage estimated $8,000.

    July 25, 1956

    At about 4:00 p.m., a small tornado caused damage along a path about 200 feet long and 15 feet wide near 4421 North 14th Street. About $250 damage was caused.

    October 23, 1956

    At about 3:30 p.m., a tornado was observed near Lake Pleasant Reservoir. High winds and terrific roaring in the clouds accompanied the tornado.

    March 7, 1958

    At 10:17 a.m., a funnel cloud was sighted in Litchfield Park, but it did not touch the ground.

    March 11, 1958

    About 5 miles south of Phoenix, a possible tornado damaged a chick hatchery to the extent of about $2,000.

    September 24, 1958

    Between 10:05 and 10:35 a.m., a well-developed tornado skipped for 4 miles across open desert 8 miles northeast of Mesa.

    July 19, 1961

    Between 7:18 and 7:25 p.m., a funnel cloud was observed over Tempe. Funnel did not touch the ground.

    July 22, 1961

    A possible tornado destroyed two hangars and damaged a number of aircraft at Deer Valley Airport.

    September 8, 1961

    At 1:30 p.m. possible tornadoes caused damage to roofs extending from 7th Avenue and Southern across 7th Street and Broadway, to Camelback High School, to Scottsdale and to Paradise Valley.

    March 11, 1965

    At 10:37 a.m. a small funnel was observed about 20 miles east-northeast of Sky Harbor Airport. It did not touch the ground.

    December 19, 1967

    At 5;30 p.m. a small tornado moved through a Mesa subdivision from the southwest and unroofed several homes.

    July 4, 1968

    At 5:30 p.m., a small tornado destroyed a house, injuring two occupants, about 5 miles east of Mesa. Two other homes and a barn suffered considerable damage. The storm was moving toward the southwest when first sighted, then turned toward the northwest and followed a short skipping path before dissipating about 5 minutes after being sighted. $25,000 damage.

    July 20, 1968

    At 8:30 p.m., a small tornado damaged several homes in the eastern part of Phoenix near 52nd Street and Van Buren. The funnel moved toward the southwest, accompanied by a loud roaring noise but apparently remained on the ground for only a few blocks. Damages estimated at $10,000.

    October 3, 1968

    At 7:00 p.m., a storm struck the residential section of Glendale causing severe damage to two apartment buildings. Several parked automobiles were heavily damaged by falling concrete blocks. Flying glass injured several persons, hospitalized one. The tornado then followed a skipping path toward the west, causing additional damage to buildings and parked trailer-houses along the way.

    February 22, 1969

    At 1:45 p.m., a funnel cloud touched ground briefly in the open country near Deer Valley Airport. The funnel moved to the east. No damage.

    July 19, 1970

    At 7;25 p.m., a funnel cloud touched ground in the open desert country of Paradise Valley. The funnel moved toward the southwest but remained visible for only a few minutes. No damage.

    September 5, 1970

    At 4:00 p.m., a funnel cloud touched ground in Scottsdale about 1/2 mile west of Scottsdale Road moving east. It crossed Scottsdale Road at Fillmore Street and continued farther east for about 1 mile. Fences and trees were blown down and a number of roofs were damaged along the path. Length of path was 1-1/2 miles, width of path was 100 yards, about $10,000 damage to property.

    August 30, 1971

    At 5:45 p.m., a tornado touched ground for about 10 minutes in an unpopulated section of south Tempe. It then moved toward the northeast into a populated area and caused considerable property damage to homes, utilities, and trees. Several homes were completely demolished, and a number of others suffered extensive roof damage. Most of the injured were not hurt badly. Many were struck by flying glass. The tornado touched down briefly in west Mesa before dissipating. The storm was accompanied by heavy hail.

    September 14, 1971

    At about 7:15 p.m., three funnel clouds aloft were observed approaching and converging on the Treadway Ranch located near 83rd Avenue and Thomas Road. These funnels were about 50 feet wide at the bases and tapered larger to the cloud base. They touched down briefly over the corral area where there were 15 people and many prize horses. They ripped off the roof of one of the barns and did other damage to structures and equipment in the immediate area. Miraculously no people or animals were inured by the debris. Eyewitnesses stated that the first two funnels struck almost simultaneously followed by a dead calm before the third struck. A light shower attended their passage, and the tornadoes dissipated after striking the ranch. Damage was estimated at about $29,000.

    October 18, 1971

    At 1:40 p.m., a small tornado touched ground in the vicinity of 56th Street and Shea Boulevard in Paradise Valley. It moved east-northeast along the north side of Shea Boulevard and crossed Scottsdale Road, touching ground for about 15 minutes. The length of path was about 1/2 mile and the width of path was 50 yards. Two houses in its path suffered considerable damage and several others had roof damage. Total damage amounted to about $15,000. A second funnel cloud formed a short time later but did not touch the ground and lasted only for a few minutes.

    June 13, 1972

    At 7:33 p.m., a small tornado touched ground briefly near 40th Avenue and Southern avenue in southwest Phoenix. Two house-trailers were demolished, a utility pole blown down, and several trees uprooted. The length of path was about 1/4 mile. Estimated damage was about $40,000.

    June 21, 1972

    At 4:30 p.m., a small tornado caused about $15,000 property damage in Apache Junction, mostly to mobile homes.

    June 21, 1972

    At 5:05 p.m., two funnel clouds were observed together south of Tempe over open country then dissipated a few minutes after sighting. At 5:35 p.m., a funnel cloud was observed touching ground briefly over open country south of Tempe; a bluish white flash was observed at the base of the funnel.

    June 21, 1972

    At 6:30 p.m., extremely heavy wind damage to property along a 2-mile front was inflicted in the northern part of Paradise Valley. Inspection of the area by National Weather Service personnel after the storm, indicated that several tornado funnels, traveling together, were probably responsible for the destruction. One witness reported seeing two funnels close to one another at the height of the storm. There was also evidence that these funnel clouds touched ground in the vicinity of 36th Street and Camelback Road in Phoenix, then traveled northeastward into Paradise Valley. Also the pattern of damage in the area indicated that more than one vortex of high velocity winds passed through the area. Several hundred homes were either completely demolished or extensively damaged. Many homes that escaped complete destruction on the night of the 21st, were further damaged on the morning of the 22nd, when additional thunderstorms in the area caused heavy rains. The Arizona Statistical Division of Emergency Services made an estimate of the total property damage for the two-day period (June 21-22, 1972) of $10,800,000. Because of the relatively short-time internal between storms on the two days, it was impossible to estimate the tornado damage alone on the 21st.

    August 12, 1972

    At 8:00 p.m., a small tornado touched ground briefly in south Phoenix in an unpopulated area. No damage.

    September 10, 1972

    At 7:05 p.m., a tornado touched ground near the intersection of South Alma School Road and West Broadway in Mesa, moving in an east-southeasterly direction. It crossed Country Club Drive and turned northeast, dissipating near the intersection of South Mesa Drive and East Broadway. The tornado was attended by locally heavy rain and one-inch hail. Observers reported frequent cloud-to-cloud lightning near the storm and that some strokes were copper-green in color. One injury occurred when a seventeen month-old girl was cut by flying glass. Property damage was estimated at $1,000,000 by Maricopa County Emergency Services.

    October 18, 1972

    At 6:45 p.m., a tornado touched down about 1 mile east of Apache Junction. The storm was accompanied by marble-size hail and almost continuous lightning. Several mobile-homes were demolished by the wind. Most of the damage occurred near the intersection of Tomahawk Road and Scenic Road.

    October 20, 1972

    At 12:00 noon, a funnel cloud aloft was observed about 8 miles north-northeast of Phoenix. The funnel did not touch ground. No damage was reported.

    May 31, 1973

    At 4:45 p.m., the public reported a funnel cloud near 91st Avenue and McDowell Road, not touching ground. One-inch hail was reported in the same general area.

    July 7, 1974

    At 2:00 p.m., a funnel cloud a few miles south of Chandler was reported by the public. It formed in the southeast sector of the storm and dissipated as the rain began.

    August 24, 1974

    At 8:05 p.m., a small tornado, reported by the public, touched down near 193rd Avenue and West Earl Drive and destroyed a storage shed. It traveled from west to east.

    May 4, 1976

    At 2:15 p.m., a tornado was observed to be about 1 to 2 miles north of Falcon Field, east-northeast of Mesa. It tore up the desert as it moved in a westerly direction and then dissipated as it entered a citrus grove. The light dust filled column was very pronounced against the dark cloud background, and it tilted toward the east with height. There was also a very narrow, rope-like, column a short distance to the east of the main tornado, and it curved to the east with height. The tornado lasted about 12 minutes, and no property damage occurred.

    May 4, 1976

    At about 2:15 p.m. a tornado touched down about 5 miles southeast of Scottsdale Airport, as reported by the controllers in the Scottsdale Tower. The spinning dust filled column appeared to be about 40 feet in diameter, and there was much debris around the base of the column extending out for approximately 100 yards. The column was vertical up to about 800 feet and then curved to the northeast. It dissipated about 20 minutes after forming. There was no property damage.

    May 4, 1976

    At 3:03 p.m., a pilot reported a tornado over the Fountain Hills area. No damage was reported.

    March 25, 1977

    At 12:55 p.m., a pilot on the ground reported a tornado about 2 miles west-southwest of Luke Air Force Base, moved north, and lifted into the cloud at 1;00 p.m.

    July 26, 1978

    At 2:45 a.m., Maricopa Sheriff's Office reported a funnel cloud near Montezuma Peak. It was verified by radar with a hook echo at about 16 miles south-southwest of Sky Harbor International Airport.

    December 30, 1978

    At 1:56 p.m. to 2:03 p.m., a very elongated funnel cloud was observed to the north-northeast of Sky Harbor International Airport by National Weather Service personnel. At 4:30 p.m., a funnel cloud was observed by the public to be northeast of Scottsdale. At 4:55 p.m., a family of three funnel clouds was observed by a pilot to be in the Four Peaks area.

    January 25, 1979

    At 5:40 p.m., a funnel cloud was reported by the public and a pilot. It did not touch the ground, but associated strong winds destroyed one mobile home, damaged another, and tore down the rafters of a church under construction in Gilbert. At Sun Lakes, a large mobile home was overturned and heavily damaged. Numerous carports and roofs were also damaged.

    February 1, 1979

    At 2:15 p.m., to 2:20 p.m., a funnel cloud was observed to the east of Sky Harbor International Airport and moving to the east. It was observed by National Weather Service personnel on duty.

    March 28, 1979

    At about 6:30 p.m., a squall with severe thunderstorms passed through the Greater Phoenix Area. Localized severe damage was incurred along a line running from near Black Canyon Freeway and Thomas Road to beyond 32nd Street and Shea Boulevard. Many businesses and homes were either destroyed or heavily damaged. Only minor injuries were reported. Funnel clouds were observed. However, there was no confirmed sighting of a tornado. Scattered debris indicated no evidence of a tornado and damage was the result of a severe downburst. Total damage was estimated at about $5,000,000.

    January 18, 1980

    At about 5:30 p.m., funnel clouds were observed by persons in Fountain Hills. A thunderstorm with half-inch size hail, heavy rain, and vicious winds estimated at 100 m.p.h. damaged 50 residences in Fountain Hills and Scottsdale. In Fountain Hills, 4 were destroyed and 16 severely damaged. Study of the debris pattern showed a homogeneous direction, indicating a tornado was not involved. Only two persons received minor injuries. Total damage estimated at $1,000,000.

    April 30, 1980

    At 9:52 a.m., a very slender funnel cloud was sighted by Deer Valley Control Tower operators to be about 3 miles to the southwest. It extended down about 500 feet from the cloud base and then retracted in four minutes. Movement was to the east.

    September 5, 1981

    At about 7:20 p.m., a tornado touched down during a severe thunderstorm, for about one mile, in the far northern sections of Peoria and Glendale. It knocked down a section of a 69,000-volt power line, damaged several houses and mobile homes, and uprooted large trees. No injuries were reported.

    August 8, 1983

    At 5:18 p.m., during a severe thunderstorm, a small tornado touched down near 83rd Avenue and Osborn and destroyed a barn.

    August 16, 1983

    At about 5:10 p.m., a funnel cloud was sighted by the public over the western portion of Mesa.

    August 16, 1983

    At around 5:30 p.m., during a violent thunderstorm a small tornado moved from south to north about 1/2 mile west of the western edge of Sky Harbor International Airport and covered a distance of about 0.3 of a mile. It stopped a moving car and exploded the windows. It also knocked down about a dozen power line poles, one of which severely damaged several parked cars on the south side of Buckeye Road.

    April 28, 1984

    At 1:15 p.m., a pilot reported three funnel clouds three miles west of the Superstition Mountains.

    August 9, 1984

    At 8:00 p.m., a small tornado touched down just northeast of I17 and Bell Road and moved to the southwest and then veered to the northwest for a total distance of about one-half mile. Several houses were damaged.

    August 9, 1984

    At 8:00 p.m., Luke Air Force Base radar picked up an echo indicating either a tornado or a funnel cloud to the southeast. There was no visual contact and no evidence that it touched the ground.

    August 15, 1984

    At 2:45 p.m., a funnel cloud was reported by the public over the southeastern section of Mesa. It was visible for a few minutes.

    September 18, 1985

    At 3:40 p.m., a funnel cloud was reported by the public in the vicinity of El Mirage.

    April 1, 1986

    At about 7:50 a.m., over the extreme northern section of Phoenix, a series of small funnel clouds in rapid succession extended down a short distance and then drew back into the cloud base.

    November 18, 1986

    At about 5:00 p.m., a tornado hit near Apache Junction, ripped through two mobile-home parks, and damaged at least 60 homes. There were no injuries.

    February 26, 1987

    Between 3:15 and 4:30 p.m., funnel clouds were sighted at Williams AFB and Tempe.

    May 10, 1987

    at 4:40 p.m., a pilot reported a small funnel cloud 10 miles southwest of Williams AFB, just before a dust storm lowered the visibility to near zero.

    May 20, 1987

    At 4:05 p.m., a pilot reported a short-lived funnel cloud about 2 to 3 miles southeast of Falcon Field.

    November 1, 1987

    At 2:05 a.m., a pilot reported a small funnel cloud about 14 miles northwest of Phoenix. The observer on duty at Sky Harbor Airport noted several protuberances from a wall cloud to the west.

    March 2, 1988

    At 6:04 p.m., there were three reports of well-developed funnel clouds from portions of central and north-central Phoenix.

    April 16, 1988

    At 11:03 a.m., observers at Luke AFB watched several small, short-lived funnels form and dissipate over open land to the west and northwest. Movement was to the northeast.

    January 4, 1989

    At 11:00 a.m., a weak tornado was observed by National Weather Service personnel at Sky Harbor Airport. Movement was to the northeast. Some roof damage was done to businesses and a few homes near downtown Phoenix.

    September 3, 1990

    At 5:15 p.m., a small tornado touched down north of Union Hills Drive between 7th Street and 7th Avenue, on the far north side of Phoenix. It ended at 5:45 p.m., and did not cause any damage.

    SUNSHINE, CLOUDINESS, AND FOG

    AVERAGE AND HIGHEST AND LOWEST PERCENTAGE OF POSSIBLE SUNSHINE
    BY MONTHS AND YEAR OF OCCURRENCE
    1896-1995

    Month

    Average

    Highest

    Year

    Lowest

    Year

    January

    78

    100

    1924

    54

    1935

    February

    80

    99

    1924

    47

    1905

    March

    84

    99

    1988

    60

    1935

    April

    89

    98

    1954 1961 1989 1991

    68

    1926

    May

    93

    99

    1924 1927 1942 1983 1991

    79

    1992

    June

    94

    100

    1916 1917 1928 1939

    78

    1931

    July

    85

    97

    1961

    67

    1930

    August

    85

    97

    1956 1960

    64

    1935

    September

    89

    99

    1955 1956 1968 1973

    76

    1940

    October

    88

    99

    1973 1995

    65

    1972

    November

    83

    98

    1948 1956

    62

    1965 1982

    December

    77

    98

    1958

    47

    1914

    Annual

    85

    94

    1960 1989

    75

    1935

    AVERAGE ANNUAL PERCENTAGE OF POSSIBLE SUNSHINE AT PHOENIX
    AS COMPARED TO OTHER MAJOR U.S. CITIES

    PHOENIX

    85

    Detroit

    54

    New York

    59

    Albuquerque

    76

    Great Falls

    63

    Oklahoma City

    68

    Atlanta

    61

    Houston

    56

    Philadelphia

    57

    Boston

    60

    Kansas City

    63

    Pittsburgh

    49

    Buffalo

    52

    Los Angeles

    73

    Saint Louis

    58

    Chicago

    54

    Memphis

    65

    Salt Lake City

    66

    Cleveland

    51

    Miami

    73

    San Francisco

    66

    Dallas

    66

    Minneapolis

    58

    Seattle

    46

    Denver

    70

    New Orleans

    59

    Washington

    58

     

    AVERAGE NUMBER OF CLEAR, PARTLY CLOUDY, CLOUDY AND HEAVY FOG DAYS BY MONTHS
    1938-1995

     

    CLEAR

    PARTLY CLOUDY

    CLOUDY

    HEAVY FOG

    January

    13.9

    7.0

    10.1

    0.5

    February

    12.5

    6.7

    9.0

    0.1

    March

    14.4

    8.1

    8.5

    0.1

    April

    17.2

    7.3

    5.6

    0.0

    May

    20.8

    6.8

    3.5

    0.0

    June

    23.1

    4.7

    2.2

    0.0

    July

    16.6

    10.3

    4.2

    0.0

    August

    17.6

    9.6

    3.8

    0.0

    September

    21.6

    5.4

    3.0

    0.0

    October

    20.3

    6.2

    4.4

    *

    November

    17.7

    6.2

    6.1

    0.2

    December

    15.3

    6.3

    9.4

    0.5

    Annual

    211.0

    84.6

    69.7

    1.5

    *Less than .05

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 100 PERCENT SUNSHINE EACH DAY 1896-1995

    28 days

    June 12-July 9

    1928

    27 days

    June 4-June 30

    1939

    26 days

    March 4-March 29

    1988

    GREATEST NUMBER OF CONSECUTIVE DAYS WITH 0 PERCENT SUNSHINE EACH DAY 1896-1995

    3 days

    November 22-24

    1965

    Arizona Indian Proverb: "If the sun appears dead, not bright and clear, in the spring, expect poor crops and very little rain".

    WIND

    AVERAGE SPEED, PREVAILING DIRECTION, AND PEAK GUST BY MONTHS
    AND DAY AND YEAR OF OCCURRENCE

    Average Speed (mph)

    PREVAILING DIRECTION

    PEAK GUST (MPH)

    DIRECTION

    DAY

    YEAR

    January

    5.3

    East

    60

    W

    27

    1983

    February

    5.9

    East

    54

    W

    19

    1980

    March

    6.6

    East

    51 51

    W W

    1 25

    1977 1989

    April

    6.9

    East

    49 49 49

    SW S S

    16 10 2

    1976 1977 1981

    May

    7.0

    East

    59

    SSE

    20

    1954

    June

    6.8

    East

    73

    NE

    5

    1978

    July

    7.1

    West

    86

    SE

    7

    1976

    August

    6.6

    East

    78

    E

    6

    1978

    September

    6.3

    East

    75

    SW

    18

    1950

    October

    5.8

    East

    61

    W

    1

    1981

    November

    5.3

    East

    60

    W

    30

    1982

    December

    5.1

    East

    68

    W

    4

    1953

    Annual

    6.2

    East

    86

    SE

    July 7

    1976

    Arizona Indian Proverbs: "If the snow that falls during the winter is dry and is blown about by the wind, a dry summer will follow; very damp snow indicates rain in the spring".
    "When smoke rises from the bottom lands and goes to the mountain, expect an early winter".

    MEAN FREQUENCY OF OCCURRENCE OF PEAK WIND GUSTS BY MONTHS: 1970-1995

    MPH

    JAN

    FEB

    MAR

    APR

    MAY

    JUN

    JUL

    AUG

    SEP

    OCT

    NOV

    DEC

    20-24

    4

    4

    6

    8

    12

    11

    11

    10

    8

    5

    3

    4

    25-29

    2

    2

    3

    4

    4

    4

    5

    4

    4

    2

    2

    1

    30-34

    1

    1

    2

    2

    3

    2

    2

    2

    2

    1

    1

    1

    35-39

    *

    *

    1

    1

    2

    1

    3

    3

    1

    1

    1

    *

    40-44

    *

    *

    1

    1

    1

    1

    1

    1

    1

    *

    *

    *

    45-49

    *

    *

    *

    *

    *

    *

    1

    1

    1

    *

    *

    *

    50-over

    *

    *

    *

    0

    *

    *

    *

    1

    *

    *

    *

    *

    *Less than 0.5

    Example: In July, on the average, there were 11 days with peak wind gusts 20-24 mph, 5 days with peak wind gusts 25-29 mph, 2 days with peak wind gusts 30-34 mph, etc.

    ESTIMATED RETURN PERIODS OF PEAK WIND GUSTS BY MONTHS
    Based on Period of Record 1957-1995

    RETURN PERIOD (YEARS)

    10

    25

    50

    100

    200

    500

    January

    44

    52

    59

    67

    76

    90

    February

    48

    58

    66

    75

    86

    102

    March

    47

    53

    57

    63

    68

    76

    April

    47

    51

    55

    58

    62

    68

    May

    49

    55

    61

    67

    74

    84

    June

    53

    61

    68

    75

    84

    96

    July

    63

    73

    81

    90

    99

    114

    August

    63

    71

    79

    86

    95

    108

    September

    50

    55

    60

    65

    70

    78

    October

    50

    61

    70

    80

    92

    110

    November

    48

    59

    68

    78

    90

    109

    December

    39

    44

    48

    52

    57

    64

    Annual

    71

    80

    88

    97

    106

    120

    Example: This means that in the month of July, a peak wind gust of 63 mph can be expected once every 10 years, a peak gust of 73 mph once every 25 years, a peak gust of 81 mph once every 50 years, etc.

    PRESSURE
    AVERAGE AND HIGHEST AND LOWEST STATION PRESSURE BY MONTHS
    AND DAY AND YEAR OF OCCURRENCE
    1896-1995

    Station Elevation 1107 Feet
    1896-1995

    MONTH

    AVERAGE

    HIGHEST PRESSURE

    DAY

    YEAR

    LOWEST PRESSURE

    DAY

    YEAR

    January

    28.89

    29.42

    24

    1938

    28.20

    4

    1913

    February

    28.86

    29.34

    1

    1916

    28.24

    23

    1948

    March

    28.78

    29.26

    12

    1920

    28.24

    3

    1983

    April

    28.72

    29.23

    4

    1945

    28.27

    28

    1898

    May

    28.66

    29.05

    2

    1970

    28.19

    18

    1902

    June

    28.63

    28.95

    2

    1919

    28.31

    20

    1947

    July

    28.68

    28.97

    20

    1974

    28.33

    14

    1900

    August

    28.89

    28.96

    28

    1896

    28.37

    22

    1903

    September

    28.69

    29.00

    29

    1970

    28.24

    24

    1915

    October

    28.76

    29.17

    29

    1980

    28.22

    11

    31

    1928

    1981

    November

    28.84

    29.32

    18

    1969

    28.24

    30

    1982

    December

    28.89

    29.44

    24

    1898

    28.16

    13

    1984

    Annual

    28.76

    29.44

    24

    1898

    28.16

    13

    1984

     

    HIGHEST AND LOWEST SEA-LEVEL PRESSURE BY MONTHS
    AND DAY AND YEAR OF OCCURRENCE

    1896-1995

     

    HIGHEST

    DAY

    YEAR

    LOWEST

    DAY

    YEAR

    January

    30.62

    24

    1938

    29.35

    4

    1913

    February

    30.55

    1

    1916

    29.36

    23

    1948

    March

    30.45

    12

    1920

    29.37

    26

    1984

    April

    30.42

    4

    1945

    29.37

    28

    1898

    May

    30.19

    2

    1970

    29.32

    18

    1902

    June

    30.11

    2

    1919

    29.40

    20

    1947

    July

    30.11

    20

    1974

    29.43

    14

    1900

    August

    30.09

    28

    1896

    29.47

    22

    1903

    September

    30.15

    29

    1970

    29.34

    24

    1915

    October

    30.34

    31

    1981

    29.34

    11

    1928

    November

    30.50

    18

    1969

    29.37

    30

    1982

    December

    30.62

    24

    1898

    29.30

    13

    1984

    Annual

    30.62

    24 DEC 24 JAN

    1898 1938

    29.30

    13 DEC

    1984

     

    NORMAL 6-HOURLY PRESSURE CHANGES IN INCHES ENDING AT:

     

    0500M (5 am)

    1100M (11 am)

    1700M (5 pm)

    2300M (11 pm)

    January

    -0.01

    +0.06

    -0.10

    +0.04

    February

    0.00

    +0.06

    -0.10

    +0.05

    March

    +0.01

    +0.05

    -0.11

    +0.04

    April

    +0.02

    +0.05

    -0.12

    +0.05

    May

    +0.03

    +0.04

    -0.12

    +0.05

    June

    +0.03

    +0.04

    -0.12

    +0.03

    July

    +0.03

    +0.04

    -0.14

    +0.07

    August

    +0.03

    +0.04

    -0.13

    +0.07

    September

    +0.02

    +0.05

    -0.12

    +0.05

    October

    +0.02

    +0.04

    -0.11

    +0.05

    November

    0.00

    +0.05

    -0.10

    +0.05

    December

    0.00

    +0.05

    -0.10

    +0.05


    Source: NORMAL PRESSURE AND TENDENCIES FOR THE UNITED STATES, 1931-1940, Weather Bureau Technical Paper
    No. 1, 1943.

    FLYING WEATHER

    PERCENTAGE FREQUENCIES OF CEILING-VISIBILITY
    Ceiling (Feet)

    Visibility

    0

    100-200

    300-400

    500-900

    1000-1900

    2000-2900

    3000-4900

    5000-9500

    Over 9500

    Total

    0-to-1/8

    +

    +

    +

    0

    0

    0

    0

    +

    +

    +

    3/16-to-3/8

    +

    0

    0

    +

    0

    0

    0

    +

    +

    +

    1/2-to-3/4

    0

    +

    0

    +

    +

    +

    0

    +

    +

    +

    1-to-2.5

    +

    0

    +

    +

    +

    +

    +

    +

    .1

    .1

    3-to-6

    0

    0

    +

    +

    .1

    +

    .1

    .1

    .3

    .7

    7-to-15

    0

    0

    0

    +

    .1

    .1

    .7

    2.5

    44.4

    47.9

    20-to-30

    0

    0

    0

    +

    +

    .1

    .4

    1.1

    22.1

    23.7

    35-or-more

    0

    0

    0

    0

    +

    +

    .2

    .7

    26.7

    27.5

    Total

    +

    +

    +

    .1

    .2

    .3

    1.4

    4.5

    93.6

    100

    +Indicates more than 0 but less than .05 percent.

    Source: SUMMARY OF HOURLY OBSERVATIONS -- PHOENIX, ARIZONA, 1951-1960, Climatology of the United States No. 82-2.

    FREQUENCIES OF VISIBILITY-RESTRICTING PHENOMENA
    IN TOTAL NUMBER OF DAYS BY MONTHS OVER THE TWENTY-SIX YEAR PERIOD
    1965-1995

    Visibility in Miles (Equal to or Less Than)

     

    January

    February

    March

     

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    K,H

    0

    0

    12

    44

    0

    0

    1

    9

    0

    0

    0

    4

    BD

    0

    2

    4

    6

    0

    2

    4

    11

    1

    5

    8

    23

    F

    12

    15

    19

    26

    1

    1

    2

    5

    3

    4

    4

    6

    R

    0

    6

    21

    44

    0

    0

    14

    37

    0

    2

    20

    44

     

     

    April

    May

    June

     

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    K,H

    0

    0

    0

    0

    0

    0

    0

    1

    0

    0

    0

    0

    BD

    0

    5

    12

    22

    4

    13

    17

    28

    5

    12

    16

    28

    F

    0

    0

    0

    3

    0

    0

    0

    0

    0

    0

    0

    0

    R

    0

    0

    3

    13

    0

    0

    2

    7

    0

    0

    1

    2

     

     

    July

    August

    September

     

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    K,H

    0

    0

    0

    2

    0

    0

    0

    0

    0

    0

    0

    1

    BD

    12

    44

    82

    112

    18

    44

    77

    99

    8

    20

    29

    38

    F

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    1

    R

    0

    5

    13

    26

    1

    6

    16

    29

    1

    6

    12

    22

     

     

    October

    November

    December

     

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    1/4

    1

    3

    6

    K,H

    0

    0

    0

    4

    0

    3

    7

    35

    0

    0

    12

    63

    BD

    3

    5

    10

    18

    0

    1

    7

    7

    1

    1

    2

    3

    F

    1

    2

    2

    3

    6

    7

    9

    11

    11

    12

    21

    27

    R

    0

    2

    9

    19

    0

    3

    19

    35

    0

    4

    22

    53

    SYMBOL KEY K,H = Smoke and/or Haze
    BD = blowing Dust
    F = Fog (not accompanied by rain)
    R = Rain (may be accompanied by fog)


    Example: For the month of July, over the twenty-six year period, there was a total of 112 days when blowing dust reduced the visibility to 6 miles or less; on 82 of these days, it was reduced to 3 miles or less; on 44 of these days, it was reduced to 1 mile or less; on 12 of these days, it was reduce to 1/4 mile or less.

    HOLIDAY WEATHER INFORMATION

    HOLIDAY

    Average Maximum Temp

    Average Minimum Temp

    Highest Maximum Temp

    Year

    Lowest Minimum

    Year

    Frequency of 0.01 inch or more of precipitation

    New Year's (Jan 1)

    65

    40

    81

    1981

    24

    1919

    11

    Presidents Day (Feb 15-12)

    71-72

    45-46

    88

    1977 1981

    26

    1910 1964

    16*

    Easter Sunday (Mar 22-Apr 25)

    77-87

    50-58

    105

    1989

    31

    1897

    9*

    Memorial Day (May 22-31)

    96-99

    66-68

    114

    1910

    48

    1916 1917 1962 1965

    2*

    Independence Day (Jul 4)

    106

    78

    118

    1989

    63

    1912

    7

    Labor Day (Sep1-7)

    102-100

    77-75

    116

    1950

    60

    1921

    15*

    Halloween (Oct 31)

    82

    54

    96

    1988

    36

    1900

    11

    Arizona State Fair (Oct 25-Nov 15)

    84-75

    57-49

    97

    1934

    28

    1916

    9*

    Thanksgiving Day (Nov 22-28)

    72-70

    47-45

    89

    1950

    27

    1931

    13*

    Christmas Day (Dec25)

    65

    41

    78

    1980

    26

    1926

    15

    *These percentages relate to the probability of precipitation on any one day of the given period.

    WEATHER EXTREMES

    WEATHER EXTREMES FOR PHOENIX AS COMPARED TO THOSE FOR ARIZONA AND UNITED STATES


    HIGHEST TEMPERATURE (Fahrenheit)

    Phoenix

    122

    June 26, 1990

    Arizona

    128

    Lake Havasu City (June 29,1994)

    United States

    134

    Death Valley, California (July 10, 1913)


    LOWEST TEMPERATURE (Fahrenheit)

    Phoenix

    16

    January 7, 1913

    Arizona

    -40

    Hawley Lake (January 7, 1971)

    United States

    -80 -70

    Prospect Creek (25 SE Bettles), Alaska (January 23,1971) Rogers Pass, Montana (January 20, 1954)


    GREATEST PRECIPITATION IN ONE HOUR (Inches)

    Phoenix

    1.72

    August 18, 1966

    Arizona

    3.52

    Tempe Citrus Experiment Station (September 14, 1969)

    United States

    12.00

    Holt, Missouri (June 22, 1947) Kilauea Sugar Plantation Hawaii (January 24-25, 1956)


    GREATEST PRECIPITATION IN TWENTY-FOUR HOURS (Inches)

    Phoenix

    4.98

    July 1-2, 1911

    Arizona

    11.40

    Workman Creek (30 NNW Globe) September 4-5, 1970

    United States

    43.00

    Alvin, Texas July 25-26, 1979


    GREATEST PRECIPITATION IN ONE CALENDAR MONTH (Inches)

    Phoenix

    6.47

    July 1911

    Arizona

    16.95

    Crown King August 1951

    United States

    107.00

    Kukui, Hawaii March 1942

    (Continental)

    71.54

    Helen Mine, California January 1909


    GREATEST PRECIPITATION IN ONE CALENDAR YEAR (Inches)

    Phoenix

    19.73

    1905

    Arizona

    58.92

    Hawley Lake 1978

    United States

    704.83

    Kukui, Hawaii 1982

    Continental

    332.29

    MacLeod Harbor, Alaska 1976


    LEAST PRECIPITATION IN ONE CALENDAR YEAR (Inches)

    Phoenix

    2.82

    1956

    Arizona

    0.07

    Davis Dam 1956

    United States

    0.00

    Death Valley, California 1929 Bagdad, California 1913

     

    Weather Extremes

    GREATEST SNOWFALL IN TWENTY-FOUR HOURS (Inches)

    Phoenix

    1.0

    January 20, 1933; January 20-21, 1937

    Arizona

    38.0

    Heber Ranger Station December 14, 1967

    United States

    75.8

    Silver Lake, Colorado April 14-15, 1921


    GREATEST SNOWFALL IN ONE STORM (Inches)

    Phoenix

    1.0

    January 20, 1933; January 20-21, 1937

    Arizona

    67.0

    Heber Ranger Station December 13-16, 1967

    United States

    189.0

    Mt. Shasta Ski Bowl, California February 13-19, 1959

     

     

    175.4 Thompson Pass, Alaska December 26-31 1955


    GREATEST SNOWFALL IN ONE CALENDAR MONTH (Inches)

    Phoenix

    1.0

    January 1933; January 1937

    Arizona

    123.0

    Sunrise Mountain March 1973

    United States

    390.0

    Tamarack, California January 1911


    GREATEST SNOWFALL IN ONE SEASON (Inches)

    Phoenix

    1.0

    1932-1933; 1936-1937

    Arizona

    400.9

    Sunrise Mountain 1972-1973

    United States

    1122.0

    Rainier Paradise Ranger Station, Washington 1971-1972

     

    974.5

    Thompson Pass, Alaska 1952-1953


    GREATEST DEPTH OF SNOW ON THE GROUND (Inches)

    Phoenix

    1

    January 20, 1933; January 21, 1937

    Arizona

    91

    Hawley Lake December 21, 1967

    United States

    451

    Tamarack, California March 11, 1911


    HIGHEST SEA-LEVEL PRESSURE (Inches)

    Phoenix

    30.62

    December 24, 1898; January 24, 1938

    Arizona

    31.21

    Grand Canyon December 22, 1967

    United States

    31.85

    Northway, Alaska January 31, 1989


    LOWEST SEA-LEVEL PRESSURE (Inches)

    Phoenix

    29.30

    December 13, 1984

    Arizona

    29.15

    Flagstaff February 7, 1937

    United States

    26.35

    Matecumbe Key, Florida September 2, 1935


    HIGHEST WIND VELOCITY, PEAK GUST (Miles Per Hour)

    Phoenix

    115

    Dear Valley Airport: August 14,1996 (Wind speed possibly higher: wind instrument "pegged the meter" at 100 Knots, i.e., 115 MPH)

     

    101

    Luke AFB: August 29,1996

    Arizona

    115

    Deer Valley Airport, Phoenix: August 14, 1996 (see note above)

     

    101

    Luke AFB, Phoenix: August 29, 1996

     

    94

    Davis-Monthan AFB, Tucson: July 8, 1996

    United States

    231

    Mt. Washington, New Hampshire April 12, 1934