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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS65 KPSR 041130
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
430 AM MST Thu Mar 4 2021

.UPDATE.. Aviation discussion update.

&&

.SYNOPSIS... Cooler air will settle into the region today with
highs dropping back to slightly below normal readings. Increasing
high pressure into Friday will however bring a quick return to
above normal temperatures and highs in the lower 80s, lasting
through the weekend. A more unsettled weather pattern is likely
for at least the first half of next week, but rain chances on any
particular day remain fairly low. This pattern should also lead to
a cooling trend early next week with temperatures falling to
slightly below normal by next Tuesday or Wednesday.

&&

.DISCUSSION...
The strong upper level low that brought fairly widespread windy
conditions yesterday continues to track northeastward with the low
center about to enter southern Utah. Farther south into central
Arizona, weak wrap around moisture and lingering system dynamics
are bringing some isolated light showers mainly over the high
terrain north of Phoenix. This shower activity will likely
diminish completely by sunrise, with the lower deserts very likely
seeing nothing but a few very isolated light showers.

Upper level ridging will begin to move in from the west later
today, but the cooler air behind the exiting upper level low will
keep highs right around 70 degrees. Drier and warmer air will
eventually mix down to the surface beginning Friday as the ridge
axis slowly moves through Arizona. This should give around a 10
degree boost in temperatures with highs likely topping 80 degrees
over the lower deserts. Although this ridge is shown to break
down slightly into the weekend as a decaying shortwave trough
moves through the Great Basin, the warm air mass will stay put
allowing high temperatures to remain in a 80-85 degree range. Both
weekend days show around a 40% probability of Phoenix reaching 85
degrees.

Starting Sunday, there is good model agreement showing a deep
northern Pacific trough diving southward off the NW U.S. coast.
This trough is likely to result in increasing southwesterly flow
into the Desert Southwest starting Sunday, as well as a decent
stream of upper level moisture moving into our region later
Sunday. This slug of moisture should then result in a fairly
cloudy Sunday night through Monday period, but forecast soundings
show very dry air remaining below 15K feet. The cloudy skies
Monday are likely to hamper temperatures somewhat and this is
shown in forecast highs dropping into the 75-80 degree range.

For Tuesday through the middle of next week, the ensemble cluster
analysis shows the deep Pacific trough slowly digging southward to
off the California coast before eventually tracking eastward into
the Great Basin and/or our region maybe starting on Wednesday.
The model spread mainly involves slight timing as well as minimal
strength and depth differences. Overall, for being 5-7 days out,
there is fairly good agreement among the majority of the ensemble
members. This shows the most likely scenario to be a cooling trend
through the middle of next week and likely at least a period of
minimal rain chances, probably no earlier than Wednesday. At this
point, neither the GEFS or the EPS really shows any decent chances
for widespread rainfall for this next unsettled weather pattern.

&&

.AVIATION...Updated at 1130Z.

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

SCT clouds around 10kft will gradually decrease through the
morning, but a modest return could happen this afternoon. Wind
fields will be light today but we should see typical east-west
direction changes occur during the afternoon and evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

SCT clouds around 8kft will persist a few more hours then decrease
during the late morning hours. Winds will remain light through the
forecast period.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Modest high pressure will dominate the region through the weekend
bringing continued dry and warm conditions. Daily highs of 80-85
degrees are expected over the lower deserts this weekend with
increasing clouds on Sunday. Winds will occasionally be breezy
this weekend, but gusts will mostly remain below 20 mph. A more
unsettled weather pattern is likely for the first half of next
week with gradual cooling temperatures and breezier winds, but
fairly dry conditions are likely to prevail. Minimum afternoon
humidities are likely to fall into the teens most days during the
period.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Iniguez
FIRE WEATHER...Kuhlman