955
FXUS65 KPSR 031140
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
440 AM MST Wed Sep 3 2025

.UPDATE...Updated Aviation Discussion

&&

.KEY MESSAGES...

- Today will again bring chances for isolated thunderstorms with
  the best chances focused south and east of Phoenix.

- Thunderstorms with strong gusty winds, heavy rainfall and
  localized flooding will be possible on Thursday with lingering
  chances into Friday.

- Temperatures will cool over the next few days dropping to below
  normal starting Thursday and staying there through at least
  Saturday.


&&

.SHORT TERM /Today through Friday/...
The main forecast concern through the rest of the workweek will be
the threat for strong storms and the potential for heavy rainfall
Thursday into Thursday night. A fairly complex forecast scenario
is shaping up with a Pacific trough off the West Coast, a
lingering shortwave trough currently over southern California, and
enhanced moisture from TC Lorena beginning to stream northward
into our area.

At the moment, our area is under some weak subsidence with a good
amount of dry air situated across the eastern 2/3rds of Arizona.
PWATs of 1.4-1.7" remain across southeast California and southwest
Arizona and this will continue to improve and spread back to the
east today into Thursday. Eventually, guidance shows widespread
1.4-1.7" across all of the lower deserts by Thursday
afternoon/evening. Convective potential today is shaping up to be
more limited than previously expected with the 06Z HRRR finally
coming in line with the other hi-res CAMs showing only isolated
storms across the Arizona high terrain and across far southern
Arizona. We may eventually see some isolated showers and storms
into the Phoenix area later tonight, but activity is not expected
to be widespread.

As moisture continues to increase into Thursday, guidance shows
much more favorable upper level conditions as a weak jet streak
sets up putting southern and central Arizona in a difluent region,
while a wing of vorticity may also move northward into Arizona.
There is also the question of what happens with the shortwave
trough which is currently just southwest of Las Vegas. Although
this feature is likely to weaken and/or mostly dissipate by
Thursday afternoon, guidance still shows its reflection as a
trough axis setting up from central Nevada into southern Arizona.
The combination of the increased moisture, modest instability,
and the upper level forcing should allow for a good amount of
shower and thunderstorm activity from late Thursday afternoon
through at least Thursday evening. The tail end of the hi-res CAMS
hint at this potential showing convection first developing across
southeast Arizona and along the Mogollon Rim before zippering
together over south-central Arizona (including Phoenix) during the
evening hours. The potential threats should include strong to
localized severe winds, blowing dust, heavy rainfall, and
localized minor flooding. WPC has introduced a Slight Risk on the
Day 2 ERO and guidance shows a 30-50% probability of 0.5" of
rainfall across south-central Arizona. We also can`t rule out some
strong convection across southeast California and southwest
Arizona on Thursday, but this area is likely to be more
conditional and isolated.

What happens on Friday is even more uncertain as ensemble
guidance remains uncertain with what eventually happens with TC
Lorena`s remnants. The most likely scenario calls for Lorena
dissipating completely and not reaching the mainland of northern
Mexico, but there is a small minority of members maintaining some
sort of circulation and/or disturbance into Sonora to as far
northeast as far southeast Arizona. We will likely need to wait
another day or so to know what will happen to Lorena, but either
way rain chances are likely to continue for at least portions of
Arizona on Friday. PoPs do go down into Friday, but chances are
still fairly high at 30-50%.

Temperatures over the next few days will be quickly trending
downward as moisture increases and shower and thunderstorms
become more widespread. Cloud cover will also increase
dramatically by Thursday with more clouds than sunshine across the
bulk of the area. Highs today are still expected to reach into the
normal range, but highs Thursday are likely to fall short of 100
degrees across much of the lower deserts. Friday should be the
coolest day of the week with highs only reaching between 90-95
degrees across south-central Arizona to the upper 90s across
southeast California.

&&

.LONG TERM /Saturday through Tuesday/...
This weekend into much if not all of next week is likely to be
very quiet as a deep trough sets up off the West Coast providing
persistent dry westerly flow across the Desert Southwest. The
drier westerly flow should set up already on Saturday, but some
lingering moisture may still allow for some isolated convection
focused mostly across the eastern Arizona high terrain. By
Sunday, even the bulk of the lower level moisture should get
scoured out leaving virtually no chances for rain even across the
higher terrain. Forecast surface dew points are shown to still be
in the upper 50s and 60s this weekend, but then are likely to drop
into the upper 30s to mid 40s by next Tuesday. Temperatures will
also start to warm up as we dry out and this should push daytime
highs back into the normal range by early next week, but overnight
lows are likely to be quite comfortable in the mid 70s to lower
80s.

&&

.AVIATION...Updated at 1140Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation concern will be the potential for gusty outflow
winds during the latter portion of the TAF period. In the
meantime, VRB winds will be common for metro terminal through the
early afternoon until light W`rly flow eventually takes over. As
mentioned above, there are hints that a strong outflow out of the
SE may traverse the region tonight, potentially between 07-10Z.
However, confidence regarding this feature is low and therefore it
is only mentioned in a TEMPO group in the TAFs at this time. If
this boundary were to come to fruition, BLDU, especially at KIWA
and KPHX, may be observed, along with some isolated showers and
thunderstorms in the vicinity of the terminals. If this outflow is
not realized, then typical diurnal trends should prevail. Lowest
cloud bases during the forecast will hover around 10-12k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected during the next 24 hours.
Winds will be light and follow diurnal trends, with extended
periods of variability at IPL. Other than a FEW clouds originating
from distant convection passing over the terminals from distant
convection, skies should be generally clear.


&&

.FIRE WEATHER...
Increased moisture levels will result in much better chances for
wetting rainfall and a reduced wildfire threat through Friday.
The best chances for rain are likely to be later Thursday into
early Friday. Enhanced moisture availability will result in
MinRHs only falling to between 20-30% range today and 30-40% on
Thursday and Friday as temperatures drop to below normal. Outside
areas of precipitation, winds will remain fairly light and follow
diurnal trends today before favoring a southerly direction for
Thursday and Friday. Strong drying conditions will spread across
the region this weekend ending rain chances by Sunday and
eventually lowering MinRHs back into the teens by around Monday.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman