400
FXUS65 KPSR 231131
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
431 AM MST Wed Sep 23 2026

.UPDATE...12Z Aviation Discussion.

&&

.KEY MESSAGES...

- Chances for scattered showers and isolated thunderstorms are
  expected today and Thursday with the most activity focused over
  foothill and high terrain areas.

- Along with the chances for rain, gusty storm driven outflow
  winds will be possible today and Thursday, potentially leading
  to patchy blowing dust.

- Near to slightly above normal temperatures will persist through
  the coming weekend before additional cooling is expected early
  next week.

&&

.SHORT TERM /Today through Thursday/...
Broad upper level troughing remains positioned over the
Southwestern U.S. with several smaller scale disturbances within
the larger scale trough and abundant moisture from eastern Arizona
through New Mexico. The main forecast concerns for today and
Thursday will be the potential for isolated to scattered
thunderstorms which will be capable of producing strong downdraft
and outflow winds, along with very localized heavy rainfall.
Current objective analysis shows lower level easterly flow
increasing across southeast into south-central Arizona spreading
moisture westward while water vapor imagery shows multiple
disturbances south and east of our area.

For the rest of this morning and into the afternoon, the easterly
flow is expected to increase moisture levels with low level mixing
ratios of 8-10 g/kg shifting into south-central Arizona. The
forecast for this afternoon through early tonight remains somewhat
uncertain as the main convective potential should be focused well
to our east in New Mexico associated with disturbance moving north
northeastward through the state. For our area, we will fall under
larger scale ascent associated with the trough and a jet max to
our north leaving the higher terrain as the best area of focus for
shower and thunderstorm development this afternoon. Given the
available moisture and modest heating today under partly sunny
skies, forecast MUCAPE should reach 1000 J/kg over the south-
central Arizona lower deserts to 500-750 J/kg to our north and
east. Hi-res CAMs have been inconsistent with the amount of
convection for today into tonight, but they have mostly kept with
initiation over the higher terrain later this afternoon. Given a
somewhat dry environment in the lower deserts, DCAPEs of
1200-1500 J/kg are expected which should lead to high chances of
one more more outflows being generated. Even though the CAMs have
been fairly inconsistent, storm outflows are expected which in
turn may be enough to initiate further storm development over the
lower deserts this evening. These chances (20-30%) will be
contingent upon at least one fairly strong outflow, or even
colliding weaker/smaller outflows. Some iterations of the CAMs
have even suggested a large strong outflow progressing as far
west as La Paz and Yuma Counties, sparking brief showers and
storms late in the evening to as late as 2 AM tonight.

Thursday`s forecast looks even murkier as moisture is expected to
continue to spread westward through southwest Arizona into
southeast California, while the upper level ascent is likely to
remain positioned over the eastern half of Arizona. HREF shows
even higher MUCAPEs for Thursday with the bulk of area reaching
1000-1250 J/kg during the afternoon hours while an upper level
shortwave is forecast to move through southeast Arizona. However,
there seems to be even more uncertainty within the models as the
CAMs show little to no convection developing across southern
Arizona with the majority staying to our north. Given the higher
instability and at least some upper level ascent, it would seem
we`d have at least similar chances as today, but NBM PoPs are
mostly below 10% for the lower deserts. Forecast soundings do
still show weak to possibly modest convective inhibition over the
lower deserts, so like today we`d mostly have to rely on some sort
of strong outflow or outflow collisions for storms to develop
over the lower deserts. Needless to say, uncertainty remains quite
high for Thursday`s rain chances. If storms actually do get going
on Thursday, gusty winds and localized heavy rainfall will again
be possible given the expected decent instability and modest DCAPE.

&&

.LONG TERM /Friday through Tuesday/...
By Friday, the main upper level trough is forecast to shift
northeastward out of a our region leaving dry southwesterly flow
in place. Guidance shows low level mixing ratios quickly dropping
to 5-7 g/kg across the lower deserts to only 6-8 g/kg over the
Arizona high terrain. As a result, Friday will begin another dry
period with only lingering chances for some isolated showers and
maybe a few thunderstorms over the eastern Arizona high terrain.
Temperatures are forecast to remain quite stable over the next few
days with highs right around to slightly above normal and lows a
few degrees above normal.

Westerly dry flow should persist through at least Saturday with
large scale troughing remaining to our northwest while the
subtropical ridge slowly shifts southwestward from east Texas
into the interior of Mexico. This shift in the ridge is likely to
bring higher heights temporarily for our region later Friday
through Saturday, so daytime highs Saturday are likely to top out
between 100-104 degrees (4-6 degrees above normal) under mostly
sunny skies.

Forecast uncertainty increases dramatically going into early next
week as it will likely depend upon what happens with Hurricane
Polo, the positioning of the subtropical ridge, and an upper
level trough that may swing through our region on or around next
Monday. The latest NHC track for Polo has it slowly making its way
westward over the next few days before turning more to the north
this weekend, but staying west of southern Baja. This track may be
enough to help advect tropical moisture northward as far as our
area, but uncertainty remains quite high. There is a low end
potential of tropical moisture making its way northward into our
area just before the aforementioned trough swings through our
region and this could lead to chances for strong to severe storms
along with heavy rain potential on or around Monday. The more
likely scenario would involve modest moisture making its way into
our area, but still with the support of the trough. The trough may
still be strong enough to support some strong to severe storms
due to much higher than normal shear, but with less moisture it
would lower the severe threat as well as well as the threat for
heavy rainfall. At this moment, we are unsure which solution will
win out, but we expect to have a better idea by the weekend.

&&

.AVIATION...Updated at 1130Z.

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

Potential for SHRA/TSRA and gusty outflow winds will be the main
aviation concerns through this evening. Light E flow will continue
before a more pronounced E/SE wind develops after sunrise with
speeds up to 8-12 kts and occasional gusts into the mid-teens to
around 20 kts. Storms will likely develop over the high terrain
and foothills within 50 miles of the Phoenix airspace this
afternoon. These storms will likely send a NE outflow into the
valley by early this evening. Timing currently looks to be around
01Z-02Z for the arrival of this outflow with gusts reaching 30-35
mph for a brief period of time. There is still around a 20-30%
chance of TS impacting any of the terminals this evening so have
maintained a PROB30 group from 02Z-05Z. After any lingering
showers clear east of the region, winds should remain E-SE
tonight. FEW to SCT clouds bases down to 8-10K ft AGL will be
common through the TAF period with SCT to BKN mid and high clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impacts are anticipated through the next 24
hours with mostly clear skies. Winds will favor W/NW at both KIPL
and KBLH through this morning and then a shift toward E/SE by the
afternoon, with wind speeds mostly staying below 10 kts along with
extended periods of light variability.

&&

.FIRE WEATHER...
Today into tonight will bring modest chances 30-50% for showers
and thunderstorms, focused over the eastern districts, while the
western districts should mostly remain dry. Gusty outflow winds
with abrupt wind shifts are expected during the first part of the
evening. MinRHs will fall into a 15-20% range today for the
western districts and 20-25% Thursday, while the eastern districts
will fall to 25-40% today and Thursday. Winds across eastern
districts will generally maintain a east southeast direction,
frequently becoming gusty while lighter, diurnally driven winds
will persist in western districts.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Salerno/Benedict
FIRE WEATHER...Kuhlman