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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: PSR
Regional NWS Weather Office: Phoenix, AZ

FXUS65 KPSR 231811

Area Forecast Discussion
National Weather Service Phoenix AZ
1111 AM MST Thu May 23 2019

.UPDATE...Updated Aviation discussion.


An unseasonably cool low pressure system moving through the
region will bring a few light showers to central and eastern
Arizona this morning while keeping temperatures well below normal
through Friday. Warmer, but still below normal temperatures will
be seen Saturday before another mostly dry weather system affects
the region Sunday into Monday. This system will usher in another
cool air mass with high temperatures as low as the lower 80s on
Memorial Day. Gradual warming next week will eventually bring
temperatures closer to normal readings.


An unseasonably deep and cold upper level low is currently
centered over western Arizona and tracking to the northeast. As
of 06Z, the NAEFS mean 500mb low center height was at 552dm or
essentially at or near a record climatological minimum for the
date. A strong baroclinic zone over central Arizona supported by
an abnormally strong upper level jet max is aiding in a band of
light showers across Maricopa County northward into the Arizona
high country. This band will make its way eastward through the
Phoenix area through around 4-5AM with the showers slowly
diminishing across eastern Arizona by early afternoon. Rainfall
amounts will be very light with most areas seeing only a few
hundredths of an inch. The upper level low is forecast to pick up
speed later this morning, reaching north-central Arizona by 12Z
and into Utah by late morning. After the morning showers and
considerable cloudiness, skies will become mostly sunny by noon as
drier air works in from the west. The cold air mass will remain
over the region today only allowing temperatures to reach into the
upper 70s to around 80 across the lower deserts.

As the main low center books northeastward into the Northern
Plains on Friday, the large scale trough will still remain over
the Southwestern U.S. Heights and temperatures aloft will rise
enough to allow for a good rebound in boundary layer temperatures
as highs warm into the upper 80s across the deserts on Friday.
Saturday will add another couple degrees, but even with highs in
the lower 90s, this falls short of normals by around five degrees.

Models are still in good agreement showing another deep Pacific
trough diving southward along the West Coast this weekend. The low
bottoms out over central California Sunday morning before
beginning the process of rapidly filling and taking an easterly
track across the Desert Southwest through Monday. This next trough
will be a bit farther north then the current one and will be even
more moisture starved. Any rain chances with this Memorial Day
weather system should remain over the high terrain, but it will
bring another round of breezy to windy conditions and drop highs
back into the 80s.

A less active weather pattern should then take over through the
rest of next week, but considerable differences remain between the
GFS and European. The GFS points toward a much warmer solution by
late next week with 500mb heights rising to 580-584dm. The Euro
hints at another weak trough moving through our region later next
week. Either solution will bring warming conditions, but if the
GFS is correct, highs will likely top 100 degrees late next week
while the Euro would keep highs mostly in the lower 90s. The
current forecast is a blend between the two showing highs in the
lower 90s by next Wednesday and middle to upper 90s for late next


.AVIATION...Updated at 1810 UTC.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Relatively moist conditions in the lower levels persist in the
wake of the showers that moved through last night. Areas of low
stratocu (with bases generally around 6k ft) have consequently
developed, but will rise and gradually dissipate through the
afternoon. Otherwise, westerly winds will prevail this afternoon,
followed by a somewhat later than normal onset of the downslope
flow at KPHX overnight.

Southeast California/Southwest Arizona including KIPL and

Breezy conditions are expected this afternoon in the wake of a low
pressure system. Gusts up to 20 kt are possible, before subsiding
this evening and into Friday morning.

Aviation Discussion not updated for amended TAFs.


Saturday through Wednesday:
Temperatures will warm closer to normal over the weekend before
another weather disturbance moves across the districts during the
first half of next week providing another period of cooler,
unsettled weather. Winds will be fairly typical early in the weekend
with typical upslope gustiness while locally windy conditions
develop during the latter half of the holiday weekend. Wetting rains
are very unlikely, though a scattered passing light shower is
possible late in the weekend. Afternoon humidity levels in a 10-20%
range early in the weekend will increase towards a 15-25% level
later in the weekend with the cooler airmass while overnight
recovery will be fair to good. Warmer temperatures and drier
conditions will then return during the middle part of next week.


Spotters should follow standard operating procedures.





Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather