000
FXUS65 KPSR 300012
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
512 PM MST Wed Nov 29 2023

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
A low pressure system will be moving in from the west this evening
giving the Arizona high terrain a decent chance for some light
precipitation. This system will also bring much cooler weather
allowing our afternoon high temperatures to drop at or slightly
below normal through the weekend. A secondary system will move
through late Thursday into Friday bringing widely scattered
precipitation chances mainly across south-central and eastern
Arizona. High pressure and warming temperatures return early next
week.

&&

.DISCUSSION...
Upon analysis of IR WV imagery this afternoon, a low pressure
system has moved inland over California and will continue to
progress southeastward throughout the day. Afternoon high
temperatures will be in the low 70s across the lower deserts,
which is slightly above normal. Breezy conditions have already
developed across southeastern California as a result of the low
moving further inland. Breeziness will continue to increase
through the day as the low continues to move southeastward with
gusts above 30 mph possible late this afternoon and early this
evening across the western portions of Imperial County.

The trough will dig across our region late this evening through
early Friday morning. Moisture is limited for this first round
of precipitation as PWATs will be in the 0.5-0.6” range.
Precipitation chances are best eastward of a Prescott, AZ-Tucson,
AZ line with PoPs peaking at 40-55% during the overnight hours.
Areas west of this line should remain dry, although a passing
shower cannot be completely ruled out as PoPs are less than 15%.
Due to the lack of moisture, QPF will remain light and be less
than 0.10”. The NBM gives the AZ high terrain a 70% chance of
getting more than 0.01” of rain, but only a 45% chance of getting
more than 0.10” of rain.

A secondary shortwave trough will move in quickly behind as the
first one exits the area to the east. This secondary wave will
move through Arizona Thursday evening through Friday. The amount
of moisture available will be slightly better than with the 1st
round, as PWATs will be in the 0.7-0.8” range. This enhanced
moisture in conjunction with forcing from 500mb vorticity will
allow for better PoPs as well as higher QPF amounts. Activity will
spark in Yuma and La Paz Counties Thursday evening and move
eastward and into the Phoenix Metro and AZ high terrain late
Thursday night and continue into the overnight hours. Activity
will dwindle through the day on Friday and should exit the region
by late Friday evening. Since there is more moisture and better
forcing for this round of precipitation, the QPF totals will range
from 0.05-0.20” for Yuma, La Paz, and western Maricopa Counties,
0.2-0.35” for the Phoenix area, and 0.4-0.6” for the higher
terrain north and east of Phoenix. Snow levels will dip to around
6000 ft, which will cause mixed precipitation at times in the high
terrain in southern Gila County.

These shortwave troughs will not only bring us these precipitation
chances, but will also usher in cooler air. Afternoon daily high
temperatures will be below normal beginning tomorrow and lasting
through the weekend. Although dry conditions return on Saturday,
temperatures will remain below normal for the weekend due to being
under the influence of broad troughing and lower heights aloft.
Daily afternoon high temperatures, tomorrow through the weekend,
will be in the mid-to-upper 60s across the lower deserts and range
from the upper 40s to upper 50s across the high terrain. Daily
morning lows for this time frame will be at or just slightly above
normal and will range from the upper 30s to upper 40s across the
lower deserts and be in the 30s for the high terrain. Sunday
morning looks to be the coldest morning coming up and some of the
more typical coldest lower desert rural areas and even Globe may
see their first freeze or near freeze of the season. The NBM gives
areas near Miami and Globe a 30% chance of reaching freezing
Sunday morning.

Global ensemble models agree that ridging will start to build
across the region late Sunday and into Monday and will stick
around through at least the middle of next week. This will lead to
a gradual warm up with temperatures likely going back above normal
as early as Monday. The NBM gives us a 55% chance of the afternoon
high temperature going above normal on Monday. By the middle of
next week, as the ridge moves overhead, the NBM has temperatures
going back into the mid-to-upper 70s.

&&

.AVIATION...Updated at 0012Z.

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

An upper trough moving through the southwestern CONUS will lead to
variable cloudiness tonight with SCT-BKN decks of cumulus with
bases of 7-9kft ASL along with BKN-OVC layers AOA FL150. There is
a low probability (10%) of getting a light shower/sprinkle at any
given TAF site tonight. Better chances over the higher terrain
north and east of the Greater Phoenix area along with more
significant ceilings. Cloud cover begins to thin out after about
09Z before high clouds start increasing again Thursday afternoon
as another system approaches. That one will lead to more
widespread ceilings with lower bases Thursday night. As for winds,
westerly directions will prevail through this evening with a slow
transition to east/southeasterly. Anticipate redevelopment of
southwest/westerly winds in the afternoon Thursday.


Southeast California/Southwest Arizona including KIPL and KBLH:

A couple of passing weather systems will lead to westerly
breeziness for the Imperial Valley (gusts to 25kts this evening
and again Thursday afternoon). Lighter winds at KBLH favoring
SW/Wly tonight and SSWly during the afternoon. High clouds
increase during the day Thursday with lowering ceilings
approaching FL100 by 00Z Friday. FEW-SCT cumulus of 5-7kft ASL can
be anticipated Thursday afternoon.


&&

.FIRE WEATHER...
A couple of weak weather disturbances are expected to affect the
region through Friday with the first one moving through later
today and tonight and the second late Thursday into Friday. As a
result, moisture will increase over the next couple days pushing
MinRHs to above 35% on Thursday and Friday. Rain potential later
today will be confined to the Arizona high country, while the
second system is likely to bring good chances for wetting rains
over much of southern and central Arizona. Expect some breezy
conditions mainly across the western districts later today and
again areawide on Thursday. For the weekend into the first part
of next week, high pressure and drying conditions will take over
leading to a return of above normal temperatures by around Monday
and MinRHs dropping to between 20-30% by Sunday or Monday.

&&

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

$$

DISCUSSION...Berislavich
AVIATION...AJ
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion