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, 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 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 the 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 thunder showers 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.

*Unfortunately, the graph referenced in this article is unavailable as of 6/16/2024.

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 personnelcontinued 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 teletypecommunications 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).

IV.  ELEVATIONS AT THE NWS FORECAST OFFICE

PHOENIX, ARIZONA

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

IV.  TEMPERATURE

NORMAL MAXIMUM, MINIMUM, AND MEAN BY MONTHS

1961-1990

NORMAL MAXIMUM, MINIMUM, AND MEAN BY MONTHS

1971-2000

HIGHEST MEAN AND LOWEST MEAN BY MONTHS

AND YEAR OF OCCURRENCE 1896-2007

HIGHEST AND LOWEST MEAN MAXIMUM AND HIGHEST AND

LOWEST MEAN MINIMUM BY MONTHS AND YEAR OF OCCURRENCE

1896-2008

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

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

1896-1995

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 heat 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.

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:

April	May	June	July	August	September	October
0.4	5.1	20.2	26.2	23.2	13.0	1.3

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:

May	June	July	August	September
0.1	3.3	4.4	1.7	0.4

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

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

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 Higher	105 OR Higher	110 OR Higher		100 OR Higher	105 OR Higher	110 OR Higher
90		JUN 6	JUN 21	JUL 8		SEP 12	AUG 20	JUL 11
80		MAY 28	JUN 17	JUL 1		SEP 18	AUG 23	JUL 18
70		MAY 24	JUN 13	JUN 29		SEP 21	SEP 1	JUL 26
60		MAY 19	JUN 10	JUN 27		SEP 24	SEP 6	AUG 1
50		MAY 14	JUN 7	JUN 19		SEP 27	SEP 10	AUG 7
40		MAY 13	JUN 3	JUN 20		SEP 28	SEP 14	AUG 10
30		MAY 10	MAY 30	JUN 15		SEP 30	SEP 16	AUG 19
20		MAY 6	MAY 25	JUN 11		OCT 5	SEP 19	AUG 26
10		APR 20	MAY 16	JUN 4		OCT 9	SEP 23	SEP 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 days	Date	T of 1st Day	T of 2nd Day
2 days	June 25-26, 1990	120	122
1 day	July 28, 1995	121

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

# of days	Month	days	year	T of 1st day	T of 2nd day	T of 3rd day	T of 4th day
4 days	June	19-22	1968	115	115	115	115
4 days	June	25-28	1979	115	116	116	117
4 days	June	25-28	1990	120	122	118	118
4 days	July	26-29	1995	116	118	121	115
3 days	July	5-7	1905	115	116	115
3 days	July	9-11	1958	116	115	118
3 days	June	14-16	1974	115	115	115
3 days	June	24-26	1994	116	116	116

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

# of days	Start	End	Year
18 days	June 12	June29	1974
17 days	July 25	August 10	1995
10 days	June 29	July 8	1989
9 days	June 27	July 5	1907
9 days	July 3	July 11	1940
9 days	June 17	June 25	1978
9 days	June 18	June 26	1981
9 days	June 20	June 28	1990
8 days	June 11	June 18	1896
8 days	July 5	July 12	1901
8 days	July 7	July 14	1958
8 days	July 13	July 20	1978

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

# of days	Start	End	Year
28 days	June 10	July 7	1936
27 days	June 10	July 6	1974
25 days	June 23	July 17	1958
23 days	June 23	July 15	1987
22 days	June 20	July 11	1973

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

# of days	Start	End	Year
76 days	June	10-August 24	1993
64 days	June	7-August 9	1989
61 days	June	2-August 1	1935
49 days	June	30-August 17	1966
47 days	June	11-July 27	1951
47 days	June	13-July 29	1988

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

# of days	Start	End	Year
98 days	June	September 22	1973
76 days	June 10	August 24	1993
74 days	June 29	September 10	1978
70 days	June 1	August 9	1989
68 days	June 11	August 17	1966
68 days	June 7	August 13	1980

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

# of days	Start	End
120 days	November 16 1963	March 14 1964
107 days	November 27 1914	March 13 1915
105 days	November 11 1931	February 23 1932

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

# of days	Start	End	Year
18 days	January 10	January 27	1898
18 days	January 17	February 3	1933
17 days	January 23	February 8	1949

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

# of days	Sequence	Year
9 days	January 17-25	1937
9 days	January 23-31	1949
8 days	January 20-27	1898
8 days	February 2-9	1903

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

# of days	Sequence	Year
5 days	January 20-24	1937
5 days	December 13-17	1967
5 days	January 3-7	1971
4 days	January 11-14	1898
4 days	February 5-8	1903
4 days	January 4-7	1910
4 days	January 24-27	1949
4 days	January 31-February 3	1985

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

# of days	Start	End	Year
3 days	January 5	January 7	1913
3 days	January 21	January 23	1937
2 days	January 3	January 4	1949

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

# of days	Sequence	Year	T of 1st day	T of 2nd day	T of 3rd day
3 days	January 5-7	1913	42	39	41

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

# of days	Year
196 days	1989
192 days	1934
190 days	1988
188 days	1990
187 days	1987
186 days	1972
185 days	1992
180 days	1974
179 days	1954
178 days	1950

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

# of days	Year		# of days	Year
143 days	1989		112 days	1991
122 days	1988		111 days	1975
120 days	1992		110 days	1958
116 days	1973		109 days	1979
116 days	1978		109 days	1984
116 days	1987

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

# of days	Year		# of days	Year
81 days	1989		70 days	1983
75 days	1978		68 days	1977
74 days	1988		68 days	1987
73 days	1979		67 days	1933
70 days	1981		67 days	1974

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

# of days	Year		# of days	Year
28 days	1979		25 days	1981
27 days	1936		25 days	1995
27 days	1974		24 days	1990
27 days	1985		21 days	1983
27 days	1989		20 days	1988
25 days	1978		19 days	1940
			19 days	1973

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

# of days	Year		# of days	Year
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 A MAXIMUM 120 OR HIGHER
1896-1995

# of days	Year
2 days	1990
1 day	1995

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

# of days	Year		# of days	Year
127 days	1912		137 days	1941
131 days	1907		137 days	1957
131 days	1908		138 days	1896
131 days	1913		139 days	1899
136 days	1911		141 days	1903

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

# of days	Year		# of days	Year
48 days	1913		60 days	1955
53 days	1912		62 days	1908
55 days	1909		64 days	1915
59 days	1911		65 days	1907

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

# of days	Year		# of days	Year
10 days	1913		17 days	1956
12 days	1911		19 days	1912
13 days	1914		19 days	1915
15 days	1909		20 days	1923
16 days	1955		21 days	1908

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

# of days	Year		# of days	Year
0 days	1911		2 days	1904
1 day	1897		2 days	1906
1 day	1908		2 days	1912
1 day	1909		2 days	1914
1 day	1941		2 days	1916
1 day	1956

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

# of days	Start	End	Year
20 days	December 7	December 26	1916
17 days	January 11	January 27	1963
17 days	December 25	January 10	1967
15 days	January 14	January 28	1937
14 days	January 19	February 1	1904
14 days	December 22	January 4	1912
14 days	December 23	January 5	1954
13 days	January 6	January 18	1964
13 days	February 8	February 20	1966
13 days	January 3	February 15	1971

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

# of days	Start	End	Year
14 days	December 22	January 4	1912
14 days	December 8	December 21	1916
13 days	January 14	January 26	1898
12 days	December 27	January 7	1967
11 days	January 21	January 31	1904
11 days	January 18	January 28	1937
10 days	January 9	January 18	1964

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

# of days	Start	End	Year
12 days	December 8	December 19	1916
12 days	December 27	January 7	1967
11 days	December 24	January 3	1896
8 days	January 21	January 28	1937
7 days	January 12	January 18	1963
7 days	January 4	January 10	1971

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

# of days	Start	End	Year
6 days	January 4	January 9	1971
5 days	December 30	January 3	1912
5 days	January 22	January 26	1937
5 days	January 12	January 16	1963

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

# of days	Start	End	Year
4 days	January 5	January 8	1971
4 days	January 9	January 12	1964
3 days	January 6	January 8	1913
3 days	January 22	January 24	1937
3 days	January 4	January 6	1950
3 days	January 13	January 15	1963

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

# of days	Date	T of 1st day	T of 2nd day	T of 3rd day
3 days	January 6-8, 1913	17	16	19
2 days	January 7-8, 1971	19	20

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

# of days	Years		# of days	Years
39 days	1963-1964		21 days	1965-1966
30 days	1897-1898		18 days	1912-1913
29 days	1916-1917		16 days	1936-1937
24 days	1911-1912		16 days	1971-1972
24 days	1966-1967		14 days	1968-1969
21 days	1903-1904		12 days	1970-1971

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

# of days	Years		# of days	Years
15 days	1963-1964		8 days	1966-1967
10 days	1897-1898		7 days	1962-1963
9 days	1911-1912		6 days	1903-1904
9 days	1936-1937		6 days	1970-1971
8 days	1916-1917		5 days	1912-1913

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

# of days	Years		# of days	Years
5 days	1963-1964		3 days	1912-1913
4 days	1897-1898		3 days	1936-1937
4 days	1911-1912		3 days	1962-1963
4 days	1970-1971		2 days	1916-1917

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

# of days	Years		# of days	Years
3 days	1912-1913		1 day	1962-1963
2 days	1970-1971		1 day	1963-1964

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

# of days	Years		# of days	Years
0 days	1977-1978		0 days	1993-1994
0 days	1980-1981		0 days	1994-1995
0 days	1981-1982		1 day	1937-1938
0 days	1982-1983		1 day	1940-1941
0 days	1983-1984		1 day	1942-1943
0 days	1985-1986		1 day	1952-1953
0 days	1991-1992
0 days	1992-1993

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

# of days	Start	End	Year
14 days	August 18	August 31	1981
14 days	July 28	August 10	1995
11 days	July 18	July 28	1981
10 days	August 28	September 6	1983
10 days	July 5	July 14	1985
8 days	July 3	July 10	1981
8 days	July 31	August 7	1986
8 days	June 22	June 29	1988
8 days	June 24	July 1	1990
7 days	July 2	July 8	1973
7 days	July 28	August 3	1977
7 days	July 27	August 2	1980
7 days	August 24	August 30	1985
7 days	July 4	July 10	1988
7 days	July 14	July 20	1989
7 days	June 27	July 3	1994

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

# of days	Start	End	Year
40 days	July 7	August 15	1977
35 days	June 15	July 18	1988
34 days	July 30	September 1	1994
28 days	July 16	August 12	1980
27 days	July 28	August 23	1986
26 days	August 24	September 18	1983
25 days	July 20	August 13	1985
22 days	July 18	August 8	1983
21 days	July 31	August 20	1988
20 days	August 16	September 4	1981
19 days	July 23	August 10	1982
18 days	July 2	July19	1991
17 days	June 26	July 12	1984
17 days	July 29	August 14	1989

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

# of days	Year		# of days	Year
51 days	1981		26 days	1986
35 days	1983		23 days	1980
33 days	1977		23 days	1985
33 days	1989		19 days	1970
32 days	1994		18 days	1969
27 days	1982		17 days	1984
27 days	1991		17 days	1992
27 days	1995		15 days	1987

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

# of days	Year		# of days	Year
87 days	1981		60 days	1958
76 days	1977		60 days	1970
76 days	1985		59 days	1995
71 days	1983		57 days	1982
71 days	1989		57 days	1993
70 days	1994		54 days	1969
67 days	1986		54 days	1984
66 days	1991		52 days	1933
61 days	1992		49 days	1980

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

#of days	Date	Day 1	Day 2	Day 3	Day 4	Day 5	Day 6	Day7	Day 8
8 days	August 3-10 1995:	100	101	100	101	100	101	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 days	Year		# of days	Year
14 days	1995		5 days	1973
12 days	1989		5 days	1980
10 days	1990		5 days	1985
7 days	1985		5 days	1986
7 days	1994		4 days	1970
5 days	1969		4 days	1972

HIGHEST DAILY MEAN
1896-1995

Mean Temp	Date	Maximum Temp	Minimum Temp
107	June 26, 1990:	122	91
106	June 27, 1990:	118	93
104	June 25, 1990:	120	88

LOWEST DAILY MEAN
1896-1995

Temperature	Date	Maximum Temp	Minimum Temp
28	January 6 1913:	39	17
28	January 7 1913:	41	16
33	January 22 1937:	45	21
33	January 13 1963:	45	20
33	January 7 1971:	46	19

GREATEST DAILY TEMPERATURE RANGE
1896-1995

Temp Range	Date	Maximum Temp	Minimum Temp
48	June 13, 1917:	107	59
48	April 17, 1919:	96	48

LEAST DAILY TEMPERATURE RANGE
1896-1995

Temp Range	Date	Maximum Temp	Minimum Temp
3	December 10 1898:	36	33
3	November 26 1905:	60	57
3	October 24 1919:	62	59
3	February 3 1983:	52	49
3	November 25 1985:	61	58

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

	NORMAL	HIGHEST	YEAR	LOWEST	YEAR
	1961-1990	1899-1995		1899-1995
July	0	0	all	0	all
August	0	0	all	0	all
September	0	4	1965	0	most
October	17	88	1908	0	several
November	134	293	1922	36	1989
December	345	573	1911	122	1980
January	362	681	1937	110	1986
February	227	458	1939	27	1991
March	182	288	1952	6	1934
April	75	133	1965	0	several
May	8	55	1915	0	many
June	0	0	all	0	all
Season	1350	2062	1916-1917	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	HIGHEST	YEAR	LOWEST	YEAR
	1961-1990	1969-1995		1969-1995
January	8	10	1988	0	most
February	22	61	1991	0	several
March	95	210	1989	0	1973
April	222	459	1989	42	1975
May	436	688	1984	265	1971
June	696	873	1990	582	1969
July	884	1013	1989	833	1976
August	822	961	1981	763	1979
September	618	787	1983	525	1985
October	311	543	1988	151	1970
November	41	124	1988	4	1972
December	7	13	1980	0	most
Annual	4162	5245	1989	3651	1971

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	HIGHEST	YEAR	LOWEST	YEAR
	1961-1990	1951-1990		1951-1992
January	0	0	all	0	all
February	0	0	all	0	all
March	0	7	1986	0	most
April	9	84	1989	0	most
May	71	238	1984	3	1957
June	264	423	1990	41	1965
July	423	548	1989	222	1955
August	364	496	1981	183	1956
September	189	348	1983	65	1961 1964
October	24	150	1991	0	several
November	0	2	1988	0	most
December	0	0	all	0	all
Annual	1344	1934	1989	737	1964

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.

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

Month	NORMAL (1961-1990)	MAXIMUM (1896-1995)	YEAR	MINIMUM (1896-1995)	YEAR
January	0.67	5.22	1993	0.00	1912 1924 1972
February	0.68	4.64	1905	0.00	1912 1967 1984
March	0.88	4.82	1941	0.00	1933 1956 1959 1984
April	0.22	3.36	1926	0.00	1904 1920 1948 1960 1962 1989 1991 1993
May	0.12	1.31	1930	0.00	1899 1911 1913 1932 1939 1942 1945 1946 1952 1974 1983 1988 1991
June	0.13	1.70	1972	0.00	1897 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
July	0.83	6.47	1911	trace	1993 1995
August	0.96	5.33	1951	trace	1973 1975
September	0.86	5.41	1939	0.00	1953 1957 1968 1973 1988
October	0.65	4.40	1972	0.00	1898 1905 1909 1934 1950 1952 1973 1995
November	0.66	3.61	1905	0.00	1897 1903 1904 1912 1916 1917 1932 1937 1943 1945 1948 1956 1980
December	1.00	3.98	1967	0.00	1900 1901 1917 1958 1973 1981
Annual	7.66	19.73	1905	2.82	1956

YEARS IN WHICH THERE WERE 5 (the most) CALENDAR MONTHS WITHOUT MEASURABLE PRECIPITATION

1904

1938

1945

1948

1972

1973

YEARS IN WHICH ALL TWELVE CALENDAR MONTHS HAD MEASURABLE PRECIPITATION:

1921

1925

1927

1949

1965

1979

1987

1990

1992

DAILY NORMALS OF PRECIPITATION (1961-1990)

DAY	JAN TO NORM	JAN TO DATE	FEB TO NORM	FEB TO DATE	MAR TO NORM	MAR TO DATE	APRTO NORM	APR TO DATE	MAY TO NORM	MAY TO DATE	JUN TO NORM	JUN TO DATE
1	.03	0.03	.02	0.69	.03	1.38	.02	2.25	.00	2.45	.00	2.57
2	.03	0.06	.02	0.71	.03	1.41	.02	2.27	.00	2.45	.00	2.57
3	.03	0.09	.02	0.73	.03	1.44	.02	2.29	.00	2.45	.00	2.57
4	.03	0.12	.02	0.75	.03	1.47	.02	2.31	.00	2.45	.00	2.57
5	.03	0.15	.02	0.77	.03	1.50	.01	2.32	.00	2.45	.00	2.57
6	.02	0.17	.02	0.79	.03	1.53	.01	2.33	.00	2.45	.00	2.57
7	.02	0.19	.02	0.81	.03	1.56	.01	2.34	.01	2.46	.00	2.57
8	.02	0.21	.02	0.83	.03	1.59	.01	2.35	.01	2.47	.00	2.57
9	.02	0.23	.02	0.85	.03	1.62	.01	2.36	.01	2.48	.00	2.57
10	.02	0.25	.02	0.87	.03	1.65	.01	2.37	.01	2.49	.00	2.57
11	.02	0.27	.02	0.89	.03	1.68	.01	2.38	.01	2.50	.00	2.57
12	.02	0.29	.02	0.91	.03	1.71	.01	2.39	.01	2.51	.00	2.57
13	.02	0.31	.02	0.93	.03	1.74	.01	2.40	.01	2.52	.00	2.57
14	.02	0.33	.02	0.95	.03	1.77	.01	2.41	.01	2.53	.00	2.57
15	.02	0.35	.02	0.97	.03	1.80	.01	2.42	.01	2.54	.00	2.57
16	.02	0.37	.02	0.99	.03	1.83	.01	2.43	.01	2.55	.00	2.57
17	.02	0.39	.03	1.02	.03	1.86	.01	2.44	.01	2.56	.00	2.57
18	.02	0.41	.03	1.05	.03	1.89	.01	2.45	.01	2.57	.00	2.57
19	.02	0.43	.03	1.08	.03	1.92	.00	2.45	.00	2.57	.01	2.58
20	.02	0.45	.03	1.11	.03	1.95	.00	2.45	.00	2.57	.01	2.59
21	.02	0.47	.03	1.14	.03	1.98	.00	2.45	.00	2.57	.01	2.60
22	.02	0.49	.03	1.17	.03	2.01	.00	2.45	.00	2.57	.01	2.61
23	.02	0.51	.03	1.20	.03	2.04	.00	2.45	.00	2.57	.01	2.62
24	.02	0.53	.03	1.23	.03	2.07	.00	2.45	.00	2.57	.01	2.63
25	.02	0.55	.03	1.26	.03	2.10	.00	2.45	.00	2.57	.01	2.64
26	.02	0.57	.03	1.29	.03	2.13	.00	2.45	.00	2.57	.01	2.65
27	.02	0.59	.03	1.32	.02	2.15	.00	2.45	.00	2.57	.01	2.66
28	.02	0.61	.03	1.35	.02	2.17	.00	2.45	.00	2.57	.01	2.67
29	.02	0.63			.02	2.19	.00	2.45	.00	2.57	.01	2.68
30	.02	0.65			.02	2.21	.00	2.45	.00	2.57	.02	2.70
31	.02	0.67			.02	2.23			.00	2.57
Monthly Normal		0.67		0.68		0.88		0.22		0.12		0.13
DAY	JAN TO NORM	JAN TO DATE	FEB TO NORM	FEB TO DATE	MAR TO NORM	MAR TO DATE	APRTO NORM	APR TO DATE	MAY TO NORM	MAY TO DATE	JUN TO NORM	JUN TO DATE

DAILY NORMALS OF PRECIPITATION (1961-1990)

DAY	JUL TO NORM	JUL TO DATE	AUG TO NORM	AUG TO DATE	SEP TO NORM	SEP TO DATE	OCT TO NORM	OCT TO DATE	NOV TO NORM	NOV TO DATE	DEC TO NORM	DEC TO DATE
1	.02	2.72	.04	3.57	.03	4.52	.03	5.38	.02	6.02	.03	6.69
2	.02	2.74	.04	3.61	.03	4.55	.03	5.41	.02	6.04	.03	6.72
3	.02	2.76	.04	3.65	.03	4.58	.03	5.44	.02	6.06	.03	6.75
4	.02	2.78	.03	3.68	.03	4.61	.02	5.46	.02	6.08	.03	6.78
5	.02	2.80	.03	3.71	.03	4.64	.02	5.48	.02	6.10	.03	6.81
6	.02	2.82	.03	3.74	.03	4.67	.02	5.50	.02	6.12	.03	6.84
7	.02	2.84	.03	3.77	.03	4.70	.02	5.52	.02	6.14	.03	6.87
8	.02	2.86	.03	3.80	.03	4.73	.02	5.54	.02	6.16	.03	6.90
9	.02	2.88	.03	3.83	.03	4.76	.02	5.56	.02	6.18	.03	6.93
10	.02	2.90	.03	3.86	.03	4.79	.02	5.58	.02	6.20	.03	6.96
11	.03	2.93	.03	3.89	.03	4.82	.02	5.60	.02	6.22	.03	6.99
12	.03	2.96	.03	3.92	.03	4.85	.02	5.62	.02	6.24	.03	7.02
13	.03	2.99	.03	3.95	.03	4.88	.03	5.64	.02	6.26	.04	7.06
14	.03	3.02	.03	3.98	.03	4.91	.02	5.66	.02	6.28	.04	7.10
15	.03	3.05	.03	4.01	.03	4.94	.02	5.68	.02	6.30	.04	7.14
16	.03	3.08	.03	4.04	.03	4.97	.02	5.70	.02	6.32	.04	7.18
17	.03	3.11	.03	4.07	.03	5.00	.02	5.72	.02	6.34	.04	7.22
18	.03	3.14	.03	4.10	.03	5.03	.02	5.74	.02	6.36	.04	7.26
19	.03	3.17	.03	4.13	.03	5.06	.02	5.76	.02	6.38	.04	7.30
20	.03	3.20	.03	4.16	.03	5.09	.02	5.78	.02	6.40	.03	7.33
21	.03	3.23	.03	4.19	.03	5.12	.02	5.80	.02	6.42	.03	7.36
22	.03	3.26	.03	4.22	.03	5.15	.02	5.82	.02	6.44	.03	7.39
23	.03	3.29	.03	4.25	.03	5.18	.02	5.84	.02	6.46	.03	7.42
24	.03	3.32	.03	4.28	.03	5.21	.02	5.86	.02	6.48	.03	7.45
25	.03	3.35	.03	4.31	.03	5.24	.02	5.88	.03	6.51	.03	7.48
26	.03	3.38	.03	4.34	.03	5.27	.02	5.90	.03	6.54	.03	7.51
27	.03	3.41	.03	4.37	.02	5.29	.02	5.92	.03	6.57	.03	7.54
28	.03	3.44	.03	4.40	.02	5.31	.02	5.94	.03	6.60	.03	7.57
29	.03	3.47	.03	4.43	.02	5.33	.02	5.96	.03	6.63	.03	7.60
30	.03	3.50	.03	4.46	.02	5.35	.02	5.98	.03	6.66	.03	7.63
31	.03	3.53	.03	4.49			.02	6.00			.03	7.66
Monthly Normal		0.83		0.96		0.86		0.65		0.66		1.00
DAY	JUL TO NORM	JUL TO DATE	AUG TO NORM	AUG TO DATE	SEP TO NORM	SEP TO DATE	OCT TO NORM	OCT TO DATE	NOV TO NORM	NOV TO DATE	DEC TO NORM	DEC 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

1896-1995		1896-1995		1940-1995
	TRACE OR MORE	YEAR	0.01 OR MORE	YEAR	AVERAGE 0.01 OR MORE
January	16	1993	14	1993	4.1
February	17	1905	14	1905	4.0
March	16	1905	12	1905	3.8
April	18	1926	13	1926	1.7
May	12	1992	7	1992	1.0
June	8	1925 1931 1972	4	1899 1932	0.7
July	18	1984	13	1896	4.2
August	18	1963	11	1913 1929	4.8
September	16	1897	9	1939	2.9
October	12	1907 1972	9	1907 1972	2.7
November	13	1913	11	1905	2.5
December	14	1965	11	1914 1923 1926 1965	4.0
Annual	106	1905	74	1905	36.4
Least Annual	37	1953	18	1953

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 more	YEAR	0.50 or more	YEAR	1.00 or more	YEAR
January	11	1993	4	1993	2	1905
February	9	1905	6	1905	1	1908 1987
March	6	1905 1952	5	1941	3	1941
April	6	1952	3	1905	1	1926 1941
May	4	1992	1	1930 1944 1976 1979	0
June	2	1967 1972	1	1955 1965 1972	1	1972
July	7	1896	4	1955	3	1955
August	7	1963	5	1951	2	1943 1995
September	8	1939	3	1939 1984	2	1903 1939 1946 1984
October	5	1957 1974	4	1972	1	1911 1914 1932 1957 1959 1963 1972 1988 1991 1993
November	9	1905	3	1931 1982	1	1902 1905 1918 1919 1923 1931 1941 1993 1995
December	9	1914	5	1959	1	1896 1898 1902 1915 1926 1948 1926 1940 1967 1978 1984 1987 1992
Annual	43	1905	18	1905	5	1941 1946 1984
Least	9	1904	0	1953	0	Many 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 Minutes	15 Minutes	30 Minutes	1 Hour	2 Hours	24 Hours
January	0.35	0.44	0.56	0.67	0.75	0.91	1.84
	3/1926	3/1926	3/1926	3/1926	3/1926	11/1993	10-11/1993
February	0.30	0.41	0.43	0.44	0.50	0.67	1.69
	6/1935	10/1963	10/1963	10/1963	12/1936	6/1935	5-6/1935
March	0.26	0.41	0.43	0.46	0.61	0.77	2.04
	4/1941	4/1941	4/1941	12/1941	12/1941	4/1941, 3/1983	2-3/1983
April	0.32	0.61	0.75	0.76	0.76	0.92	1.66
	19/1951	19/1951	19/1951	19/1951	19/1951	8/1926	5-6/1926
May	0.35	0.45	0.53	0.59	0.60	0.61	1.12
	20/1979	20/1979	20/1979	20/1979	20/1979	20/1979	4-5/1930
June	0.30	0.40	0.52	0.62	0.92	1.20	1.64
	12/1955	22/1972	22/1972	22/1972	22/1972	22/1972	21-22/1972
July	0.50	0.70	0.91	1.15	1.30	1.47	4.98
	24/1978	26/1952	26/1952	17/1908	26/1917	2/1911	1-2/1911
August	0.90	1.14	1.17	1.23	1.72	1.81	2.72
	16/1983	16/1983	16/1983	20/1978	18/1966	6/1918	27-28/1951
September	0.68	1.00	1.14	1.27	1.41	2.20	3.06
	16/1969	16/1969	16/1969	16/1969	4/1939	4/1939	3-4/1939
October	0.68	0.72	0.72	0.86	0.93	1.03	2.32
	1/1981	1/1981	1/1981	30/1928	30-31/1928	30-31/1928	14/1988
November	0.36	0.38	0.40	0.54	0.67	0.75	2.40
	10/1931	10/1931 23/1919	23/1919	14/1918	14/1918	27/1919	9-10/1923
December	0.13	0.22	0.28	0.38	0.52	0.68	1.92
	13/1975	19/1967	13/1975	19/1967	7/1986	19/1967	30-31/1915
Annual	0.90	1.14	1.17	1.27	1.72	2.20	4.98
	16 AUG 1983	16 AUG 1983	16 AUG 1983	16 SEP 1969	18 AUG 1966	4 SEP 1939	1-2 JUL 1911

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

14 days	January	5-18	1993	total	5.12
10 days	July	22-31	1921	total	0.38
10 days	December	3-12	1926	total	2.50
9 days	January	9-17	1897	total	3.59
9 days	December	12-20	1967	total	3.98
9 days	February	13-21	1980	total	2.09
9 days	July	10-18	1984	total	0.49

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

10 days	December	3-12	1926	total	2.50
9 days	February	13-21	1980	total	2.09
9 days	January	10-18	1993	total	3.11
8 days	January	9-16	1897	total	3.59
7 days	January	15-21	1917	total	1.62
7 days	December	13-19	1967	total	3.98

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

4 days	February	12-15	1931	total	2.83
4 days	December	12-15	1932	total	1.69

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

3 days	February	12-14	1931	total	2.48
3 days	February	5-7	1935	total	2.48
3 days	March	12-14	1941	total	2.67
3 days	August	27-29	1951	total	3.77

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

2 days	January	9-10	1905	total	2.69
2 days	July	1-2	1911	total	5.49
2 days	July	25-26	1936	total	2.35
2 days	July	17-18	1946	total	2.31
2 days	September	17-18	1946	total	2.65
2 days	July	24-25	1955	total	2.05

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

91 days	January	6 1984-April 5	1984
88 days	October	17 1917-January 12	1918
88 days	April	10 1945-July 6	1945
79 days	October	7 1916-December 24	1916
77 days	April	23 1913-July 8	1913
74 days	March	29 1991-June 10	1991
72 days	April	26 1974-July 6	1974

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

160 days	December 30 1971-June 6 1972
143 days	March 2 1960-July 22 1960
125 days	July 16 1973-November 17 1973
119 days	March 24 1904-July 20 1904
118 days	February 4 1899-June 1 1899
117 days	March 11 1970-July 5 1970
117 days	March 27 1989-July 21 1989
114 days	March 11 1968-July 2 1968
114 days	March 28 1991-July 19 1991
105 days	September 1 1938-December 14 1938
105 days	March 24 1945-July 6 1945
104 days	October 1 1917-January 12 1918
102 days	April 6 1909-July 16 1909

AMOUNTS AND DATES OF ALL SNOWFALLS, 1896-1995

AMOUNT
1.0 inch	January 20 1933
1.0 inch	January 20-21 1937*
0.5 inches	February 2 1939
0.4 inches	December 21-22 1990
0.2 inches	March 12 1917
0.1 inches	November 28 1919
0.1 inches	December 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 1898	February 1 1939	December 25 1974
December 10 1898	February 8 1939	March 3 1976
January 20 1904	February 9 1939	February 2 1985
December 5 1909	April 1 1949	February 3 1985
December 25 1911	January 12 1951	February 4 1985
May 1 1915	January 13 1962	January 15 1987
December 25 1916	January 17 1962	March 21 1991
February 18 1918	December 13 1967	March 27 1991
May 9 1930	December 20 1968	February 4 1994

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	17	25	27	24	14	6	21	47	31	24	13	15
2	19	26	34	19	16	7	24	48	33	22	12	17
3	25	21	36	17	11	11	21	48	26	18	10	21
4	16	25	31	17	14	12	18	48	27	19	11	24
5	23	23	28	11	13	6	20	42	29	17	11	21
6	24	35	13	17	7	11	28	37	27	15	12	22
7	19	33	17	15	8	7	33	45	25	13	17	14
8	22	32	19	19	9	6	30	42	23	9	18	22
9	21	35	22	20	14	8	26	46	18	13	17	25
10	28	24	31	11	13	10	36	49	31	9	14	27
11	27	28	26	16	14	7	34	45	25	17	14	19
12	24	28	28	17	9	7	36	47	25	16	20	30
13	27	21	24	18	7	11	33	39	26	14	15	19
14	28	19	23	11	9	5	38	44	21	14	19	21
15	20	28	19	17	8	5	51	39	13	20	22	17
16	27	26	15	14	12	4	50	43	17	13	23	22
17	27	19	16	15	14	9	48	43	19	12	18	18
18	20	16	22	16	12	9	35	41	25	14	21	18
19	31	29	23	9	11	7	40	39	17	19	10	22
20	27	27	23	6	13	8	38	32	18	14	12	24
21	23	29	26	18	7	12	54	31	13	14	15	23
22	19	18	23	19	8	9	48	40	28	13	18	22
23	22	17	26	10	10	8	52	46	18	14	21	20
24	21	19	22	10	8	9	47	42	21	19	22	13
25	26	22	24	12	8	10	52	36	18	7	17	23
26	21	27	29	14	7	10	51	40	20	6	16	22
27	29	25	18	23	7	9	49	26	19	15	15	27
28	27	15	25	17	9	18	41	32	17	16	17	28
29	24	8	20	16	11	18	49	42	17	19	15	26
30	20		13	10	8	15	54	29	20	16	13	21
31	18		13		9		42	31		13		19
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	11	18	18	14	6	1	5	26	17	14	11	7
2	10	20	25	10	5	4	11	24	17	13	6	11
3	20	18	27	5	5	7	10	30	16	15	4	13
4	10	18	21	7	6	4	7	24	10	15	4	18
5	19	13	16	9	6	0	8	22	21	13	7	15
6	15	20	8	9	4	3	10	23	14	10	6	11
7	13	24	7	6	5	4	15	21	12	8	10	11
8	13	27	17	6	3	2	11	21	10	3	12	13
9	12	24	15	6	5	2	10	26	4	10	10	16
10	18	19	22	4	7	3	11	18	14	6	13	20
11	24	19	14	11	4	0	15	22	17	6	11	14
12	16	20	20	11	5	4	11	27	14	7	10	17
13	20	14	11	5	2	4	11	17	18	6	10	14
14	17	13	15	3	5	1	13	20	15	10	13	11
15	13	20	12	7	4	3	22	22	6	11	14	13
16	19	17	12	8	4	1	22	16	5	11	11	15
17	22	14	12	6	3	5	28	20	8	7	12	16
18	15	12	12	7	5	3	17	20	14	11	13	15
19	14	24	8	7	5	4	15	17	10	6	7	17
20	14	16	15	5	5	3	24	15	9	7	8	17
21	14	22	14	9	2	5	22	16	10	9	11	19
22	10	13	16	16	4	5	26	23	14	8	14	16
23	16	10	14	4	1	3	24	23	15	9	15	13
24	12	13	15	5	3	1	30	16	10	9	12	11
25	16	17	17	1	1	2	22	16	10	6	13	15
26	12	16	19	5	1	3	28	21	11	5	9	18
27	17	12	13	14	2	1	18	18	11	10	12	16
28	20	6	14	15	3	5	24	15	7	9	15	18
29	18	8	12	10	5	4	26	23	10	13	10	21
30	18		6	5	1	6	25	16	13	14	7	8
31	10		8		1		18	12		11		15
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	5	8	10	7	3	0	4	12	10	7	5	2
2	6	10	16	4	1	3	5	9	8	4	5	6
3	11	9	13	1	0	1	1	18	4	7	1	6
4	6	10	9	4	5	1	3	11	4	6	1	11
5	10	5	6	5	4	0	3	12	12	9	4	10
6	12	12	4	6	1	1	5	11	6	5	3	7
7	6	12	2	1	3	0	6	9	7	3	4	6
8	6	9	11	4	1	2	5	6	8	3	6	6
9	5	11	6	4	3	0	1	11	3	4	7	10
10	12	16	12	1	3	1	4	7	4	2	8	13
11	14	11	9	8	1	0	8	13	6	2	5	8
12	6	10	12	4	3	3	4	12	11	5	9	11
13	15	9	7	1	0	0	4	5	12	2	5	10
14	4	12	7	1	3	0	9	6	5	6	7	9
15	10	12	9	5	1	0	10	12	0	2	9	12
16	8	4	9	5	0	0	11	10	5	7	9	8
17	11	3	5	5	0	3	13	9	5	5	7	8
18	12	5	5	3	0	1	11	9	9	9	6	8
19	4	7	6	5	2	1	6	11	4	5	4	11
20	9	4	8	1	5	0	9	8	5	2	6	6
21	7	9	5	4	1	3	12	7	5	4	8	12
22	4	5	7	9	1	3	10	9	5	3	10	9
23	4	5	8	3	1	1	9	9	7	6	12	6
24	5	7	4	2	2	1	14	10	6	1	7	5
25	11	9	8	1	0	2	15	7	6	3	5	11
26	5	6	12	1	1	0	12	11	6	3	5	11
27	6	7	8	8	0	0	9	10	8	4	7	8
28	6	6	7	9	2	1	9	7	5	7	9	11
29	11	1	5	4	0	0	11	14	6	7	5	8
30	10		1	1	0	3	11	1	4	9	6	6
31	6		6		1		9	6		6		10
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	0	5	9	2	1	0	2	4	6	5	3	2
2	3	4	9	1	1	0	5	4	2	2	3	4
3	9	5	8	1	0	1	0	10	1	5	1	3
4	4	6	6	1	3	0	0	4	1	3	2	3
5	4	4	6	3	1	0	0	11	6	4	2	5
6	6	6	1	4	0	0	3	6	3	3	3	3
7	4	8	1	0	0	0	5	5	5	1	3	4
8	2	2	2	1	0	0	3	3	4	1	3	5
9	2	5	5	3	3	0	0	6	3	3	2	9
10	8	8	7	1	3	1	3	1	2	1	8	8
11	8	6	6	5	0	0	5	5	3	2	4	5
12	3	6	8	1	0	1	4	8	5	1	5	4
13	6	4	5	0	0	0	1	4	9	0	4	8
14	1	6	5	1	0	0	3	4	2	5	3	5
15	5	7	5	1	0	0	6	5	0	2	4	8
16	6	1	6	4	0	0	9	6	1	4	3	1
17	8	1	4	3	0	0	10	3	4	1	4	6
18	7	3	0	0	0	1	7	5	6	6	3	7
19	1	5	1	1	0	0	4	4	2	4	3	7
20	6	3	3	1	2	0	5	5	4	2	1	3
21	3	5	1	2	1	1	8	5	1	2	4	8
22	1	1	4	4	0	1	4	2	2	3	4	4
23	1	0	4	3	0	1	3	6	3	2	10	2
24	3	5	1	0	1	1	9	7	6	0	4	4
25	5	2	2	1	0	1	10	4	2	0	5	6
26	2	3	7	0	0	0	6	6	6	3	5	6
27	4	4	6	1	0	0	6	6	7	2	4	5
28	5	4	6	6	1	1	5	6	5	5	4	10
29	8	1	4	0	0	0	5	8	6	4	4	4
30	6		0	0	0	0	5	0	4	6	5	4
31	2		3		0		3	3		1		7
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	0	0	4	0	0	0	1	3	2	2	2	0
2	0	0	3	0	0	0	3	1	1	1	0	0
3	5	2	2	1	0	0	0	4	0	2	0	2
4	3	3	3	0	2	0	0	1	1	2	1	1
5	0	2	2	2	0	0	0	7	3	1	1	2
6	2	2	0	1	0	0	0	2	0	2	0	1
7	2	1	0	0	0	0	1	2	2	0	0	2
8	0	1	0	1	0	0	1	1	2	1	0	2
9	1	1	3	0	0	0	0	0	2	2	1	4
10	4	1	3	1	1	0	0	0	1	1	4	4
11	3	1	2	3	0	0	0	0	1	0	3	4
12	1	3	2	0	0	1	2	2	4	0	2	1
13	1	2	2	0	0	0	1	0	4	0	2	4
14	1	3	1	0	0	0	0	2	2	1	2	1
15	2	2	2	0	0	0	3	2	0	2	2	3
16	2	1	3	1	0	0	2	2	1	0	1	0
17	3	0	1	0	0	0	4	1	3	0	1	1
18	1	1	0	0	0	0	2	1	4	3	2	4
19	1	1	1	1	0	0	2	1	0	2	1	3
20	2	1	1	0	1	0	2	2	0	0	1	0
21	1	2	0	0	0	0	3	2	1	0	2	1
22	0	0	1	1	0	1	1	1	0	0	1	1
23	0	0	0	2	0	1	0	1	2	2	4	1
24	1	3	0	0	0	0	5	3	2	0	1	3
25	4	1	2	0	0	0	4	2	0	0	1	2
26	0	2	3	0	0	0	3	3	3	0	2	1
27	1	1	2	0	0	0	4	2	3	2	1	2
28	2	1	3	1	0	0	1	3	4	2	1	4
29	2	0	0	0	0	0	1	2	3	0	2	1
30	2		0	0	0	0	1	0	0	4	1	2
31	1		0		0		2	2		1		3
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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

DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
1	0	0	0	0	0	0	1	2	1	0	1	0
2	0	0	0	0	0	0	1	1	1	0	0	0
3	0	1	1	0	0	0	0	1	0	1	0	0
4	0	0	1	0	0	0	0	0	1	0	0	0
5	0	0	0	1	0	0	0	2	1	0	0	0
6	0	0	0	0	0	0	0	1	0	1	0	0
7	0	0	0	0	0	0	0	0	0	0	0	1
8	1	0	0	0	0	0	0	0	2	1	0	1
9	1	0	0	0	0	0	0	0	0	0	0	0
10	1	0	0	0	0	0	0	0	1	0	1	1
11	1	0	0	1	0	0	0	0	1	0	1	0
12	1	0	1	0	0	0	1	0	2	0	1	0
13	0	0	0	0	0	0	0	0	2	0	0	1
14	0	0	1	0	0	0	0	2	1	1	2	1
15	0	0	0	0	0	0	0	1	0	0	0	0
16	1	0	1	0	0	0	1	1	1	0	0	0
17	1	0	0	0	0	0	2	0	2	0	0	1
18	0	0	0	0	0	0	1	1	1	0	0	1
19	0	0	0	0	0	0	0	0	0	2	0	0
20	0	0	0	0	0	0	1	1	0	0	1	0
21	0	0	0	0	0	0	1	0	0	0	0	0
22	0	0	0	0	0	1	1	0	0	0	0	0
23	0	0	0	0	0	0	0	0	0	0	0	0
24	0	1	0	0	0	0	2	1	0	0	0	0
25	0	0	0	0	0	0	3	0	0	0	0	0
26	0	0	1	0	0	0	3	0	2	0	1	0
27	0	0	0	0	0	0	1	1	1	2	1	1
28	0	0	0	0	0	0	1	0	1	0	0	0
29	1	0	0	0	0	0	1	0	1	0	0	0
30	1		0	0	0	0	1	0	0	1	0	2
31	0		0		0		0	0		1		0
DAY	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC

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 DAY	2ND DAY	3RD DAY	4TH DAY	5TH DAY	6TH DAY	7TH DAY	8TH DAY
January	15.4	3.2	1.1	0.4	0.2	0.1	0.1	0.1
February	17.1	3.9	1.5	0.5	0.3	0.1	*	*
March	14.7	3.2	1.2	0.4	0.2	*	0.0	0.0
April	7.7	1.6	0.3	0.1	*	0.0	0.0	0.0
May	3.8	0.6	0.1	0.0	0.0	0.0	0.0	0.0
June	3.1	0.5	*	0.0	0.0	0.0	0.0	0.0
July	17.4	2.9	0.7	0.3	0.1	0.1	0.0	0.0
August	20.3	3.2	0.9	0.3	*	0.0	0.0	0.0
September	12.1	2.2	0.7	0.2	0.1	*	0.0	0.0
October	9.4	1.8	0.5	0.1	0.0	0.0	0.0	0.0
November	10.0	2.5	0.7	0.1	*	0.0	0.0	0.0
December	14.6	2.8	1.0	0.2	0.1	0.1	0.1	*

* Less than .05 percent
For 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".

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

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.

DESCRIPTION OF KNOWN TORNADOES AND FUNNEL CLOUDS IN THE

GREATER PHOENIX AREA: 1955-1990

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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

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	*	*	*	*

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

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: (Time of Day)

	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

FLYING WEATHER

PERCENTAGE FREQUENCIES OF CEILING-VISIBILITY (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

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

+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

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