192 
FXUS65 KPSR 250015
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
515 PM MST Wed Sep 24 2025

.UPDATE...Updated 00Z Aviation Discussion.

&&

.KEY MESSAGES...

- Warmer-than-nomral temperatures will be common across the 
  region through Thursday with lower desert highs near 105 
  degrees.

- Shower and thunderstorm chances begin to increase Thursday, 
  with potential activity focused over areas to the east of 
  Phoenix.

- Rainfall activity becomes more widespread across south-central 
  and eastern Arizona Friday. Strong to severe storms will be 
  possible along with locally heavy rainfall that could lead to 
  flooding.

  
&&

.SHORT TERM /TODAY THROUGH THURSDAY/...
WV imagery reveals high pressure across much of the Intermountain 
West in between a closed low spinning just off the California Coast 
and another trough stretching into the Central Plains. With ridging 
overhead, conditions across the Desert Southwest this afternoon will 
remain quiet while day-to-day temperatures see a bit of an increase 
compared to what was observed yesterday. Readings this afternoon 
across the lower deserts will hover around 105 degree, a good 5-8 
degrees above normal for late September. As a result, widespread 
moderate, to locally major, HeatRisk will make a return. These 
HeatRisk levels, especially areas in the major category, are 
primarily driven by the spread between forecasted values and the 
normal highs during this point in the year which are now in the 
upper 90s. Previous extreme heat episodes this year have been 
headlined by temps that have been around 10 degrees warmer compared 
to what can be expected both today and tomorrow. Even though 
forecasted highs will be relatively abnormal for this time of year, 
they are not uncommon compared to what we have seen over the past 3-
4 months, so no Extreme Heat products will be issued. Nonetheless, 
heat precautions should continued to be taken into account if you 
plan on being outdoors during the hottest portion of the day.

The aforementioned Pacific Low will eventually meander onshore by 
Thursday morning and will set a pattern change in motion for the 
remainder of the week and into the weekend. Before we get to bigger 
changes, ridging will still be overhead but the axis will have 
shifted further east. As mentioned above, warmer-than-normal 
temperatures will continue with areas of moderate to major 
HeatRisk once again. The once exception will be out in southeast
California where readings will be slightly cooler due to the
proximity to the westward disturbance. The other forecast 
parameter for Thursday will be increasing moisture that will lead 
to rising shower and thunderstorm chances, mainly for south- 
central Arizona. Favorable upper-jet dynamics, combined with that 
increase in moisture flux, will promote convective activity 
Thursday afternoon and evening, with the majority of it focused 
over areas to the east of Phoenix. Main concerns will be gusty 
outflow winds and isolated heavy rainfall. Confidence for rainfall
coverage around the Phoenix metro and lower desert areas of 
Maricopa and Pinal Counties is not as high, but some isolated 
activity cannot be completely ruled out. If shower and storms over
these areas were to be realized, they will be heavily reliant on 
outflow boundaries from distant activity. Due to higher-than-usual
moisture and dynamic support, convection will continue to be 
possible overnight for areas from Phoenix eastward. 

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/... 
Friday still holds fairly high potential for thunderstorm impacts
across south-central and eastern Arizona. Models are in very good
agreement showing the low moving southeastward into southeast
California during the daytime Friday. Even though this low is not
expected to be as strong as other transition type systems that 
have brought severe weather outbreaks for our region, it still
could end up being quite the impactful weather system. As the low
enters our region on Friday, south southeasterly low and mid 
level flow will increase further. We are likely to see a narrow
corridor of high instability building across our area by Friday
morning with MUCAPEs of 1500-2000 J/kg. The ingredients are likely
to be there for a line or a cluster of strong to severe storms to
develop somewhere across Maricopa, Pinal, and Gila Counties during
the first part of the afternoon as upper level forcing becomes 
maximized. Forecast 0-6km bulk shear looks to be the strongest 
during the morning hours Friday before gradually weakening during 
the afternoon. It's not impossible for some strong to severe 
storms to develop during the morning hours, but it is more likely 
to occur during the afternoon hours Friday. Strong to severe wind 
gusts, moderately large hail, and heavy rainfall will all be 
possible on Friday. 

Moisture levels on Friday are not expected to be excessively high
with PWATs as high as 1.1-1.3" in a narrow corridor, but low 
level mixing ratios will be quite good at 10-11 g/kg. The heavy 
rainfall and flood threat will mostly come from persistent showers
and thunderstorms training over the same area over a period of 
several hours. Average forecast rainfall amounts from late 
Thursday through Friday are currently between 0.25-0.75" over the 
Phoenix area to 1-2" across the high terrain east of Phoenix. At 
this point in time, it seems quite plausible a few locations will 
see localized higher rainfall amounts of 2-3". However, any 
drastic change in the cut-off low's strength and eventual track 
may cut back on our forecast rainfall amounts.

Higher uncertainty is seen for Friday night and Saturday as the
cut-off low will likely begin to weaken and the position of the
low center is a bit uncertain. We are likely to still see decent
(30-40%) rain chances across a good portion of the area during
this time, potentially extending through southwest Arizona into
southeast California as the flow should temporarily shift out of 
the east advecting better moisture westward. We are likely to lose
a good amount of our upper level jet forcing by Friday night, but
some residual forcing may still be in place across eastern 
Arizona. Overall, any additional rainfall amounts beginning Friday
night should be on the lighter side with the flood threat likely 
ending. We may even see rain chances extend into Sunday depending 
on how long it takes for the low to eventually exit the region to 
the north.

Temperatures will take a dive starting Friday with daytime highs
at most in the low to mid 90s. Some lower desert locations across
south-central Arizona may even fail to reach 90 degrees on Friday
depending on how early the convection starts. The lower heights
from the cut-off low will persist through the weekend with highs
likely only topping out in the upper 80s to around 90 degrees on
Saturday and Sunday, or 5-8 degrees below normal. Beyond Sunday, 
forecast uncertainty remains somewhat high as a large Pacific 
trough is likely to gradually shift southward along the northern 
part of the West Coast. This should help to initially raise 
heights over our region early next week, but it may eventually get
close enough to lower heights again. For now the NBM temperature 
forecast shows highs remaining below normal through at least 
Monday before inching back to near normal during the middle part 
of next week.

&&

.AVIATION...Updated at 0015Z. 

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will remain light into the overnight hours with speeds
generally aob 5 kt, with extended periods of light and variable
winds. Overall winds may tend to favor a NW'rly component tonight
before going SE'rly during the overnight hours. Winds will then go
SSE'rly late tomorrow morning with speeds generally aob 10 kt,
with some occasional gusts into the teens. Then in the afternoon
(21-22Z) winds will go SW'rly, again with some occasional gusts
into the teens possible. By the late afternoon/early evening winds
will gust into the upper teens to near 20 kt, and a TEMPO group
has been added for this in the KPHX TAF. A few vicinity
showers/storms may develop in/around the Phoenix Metro tomorrow
evening, however, confidence is too low (<30%) at this time to
include in the TAFs. However, some robust storms are expected 
east of the Phoenix Metro, so we will have to watch for outflows 
out of the east (E/SE/NE). If there are colliding outflows, 
chances for storms will go up. Skies will remain mostly clear 
through tomorrow morning until FEW cumulus clouds, with bases aoa 
8 kft, will start to develop for the afternoon and evening hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
At KIPL, SE'rly wind, with speeds aob 6 kt, will continue through
02Z before going W'rly. Speeds this evening through early tomorrow
afternoon will generally be aob 10 kt. By tomorrow afternoon W'rly
winds will gust into the 20-25 kt range. At KBLH, winds will
remain light and variable, with speeds aob 5 kt, through tomorrow
morning before going SW'rly. Around 20Z, winds will start to gust
into the upper teens to near 20 kt. Skies will remain clear. 

&&

.FIRE WEATHER...
Hot and dry conditions will continue today with moisture and rain
chances beginning to increase on Thursday. Expect isolated to 
scattered thunderstorms over the eastern districts by Thursday
evening with chances increasing into Friday. MinRH values will
hover around 20% today before increasing Thursday into Friday with
values upwards of 50% over the eastern districts on Friday. Winds
will follow familiar diurnal trends today and most of Thursday
with some breeziness likely on Thursday. The slow-moving low 
pressure system impacting the region late this week should lead to
widespread wetting rains across the eastern districts on Friday
and possibly Saturday. Below normal temperatures and elevated
humidities are expected for Friday and through the weekend.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from Friday morning through Friday evening for 
     AZZ545-547-549-552-553-555>558-560>563.

CA...None.
&&

$$

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