878 
FXUS65 KPSR 251214
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
514 AM MST Thu Sep 25 2025

.UPDATE...Updated Aviation Discussion.

&&

.KEY MESSAGES...

- Today will again bring hot temperatures across much of the lower
  deserts with highs around 105 degrees in south-central Arizona.

- Shower and thunderstorm chances will begin to increase today,
  particularly across the eastern Arizona high terrain where a few
  strong storms will be possible along with localized heavy
  rainfall.

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

- Cooler than normal temperatures are expected Friday and through
  the weekend with lingering chances for showers and isolated
  storms on Saturday.
  
&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
The next couple of days will see a big increase in shower and
thunderstorm chances across much of Arizona with the focus of the
highest potential impacts across southeast into south-central 
Arizona. The main forecast concerns will be the chances for a few 
severe thunderstorms and the enhanced potential for training 
thunderstorms producing heavy rainfall and localized flooding. 

Current objective analysis shows an upper level closed low
centered near San Francisco and upper level ridging over Arizona
into Utah. This upper low is forecast to mostly get cut off from
the main flow later today while drifting to the southeast.
Moisture return into southern and central Arizona will pick up 
later this morning into the afternoon with the best moisture
focused across southeast Arizona northward to the Mogollon Rim. As
the cut-off low shifts more into our region later today, it will 
lead to increasing diffluence aloft combining with increasing 
instability with MUCAPEs to around 1000 J/kg. Hi-res CAMs 
generally all agree on scattered showers and thunderstorms 
developing from just east of Tucson northward through Gila County 
by mid afternoon. Given the forecast instability and steep lapse 
rates, a few strong to severe storms are likely this afternoon 
across Gila County. Localized heavy rainfall will also be 
possible, but the biggest threat for heavy rain and flooding today
looks to be across far southeast Arizona into the White 
Mountains.

A westerly steering flow should keep the high terrain convection
this afternoon from spreading much farther to the west toward the
lower deserts, but we anticipate a modestly strong westward
propagating outflow to reach central Pinal and eastern Maricopa
Counties by early evening. The outflow winds will definitely be
capable of producing blowing dust, some of which may be dense
across central Pinal County. The outflow may also be strong and/or 
deep enough to trigger some new convection into the lower deserts.
Any storms that do form over the lower deserts may become strong,
but with waining instability due to the loss of daytime heating 
the severe threat is likely to be limited.

Isolated shower and thunderstorm chances will continue tonight 
into early Friday, but guidance has been inconsistent with the 
placement and the areal extent. Hi-res CAMs seem to agree not a 
whole lot of activity will occur tonight/early Friday morning, but
this may very well be underdone due to the increasing upper level
forcing as the low moves into southeast California and more 
focused moisture advection into south-central Arizona. 

Much better chances for convective development will exist by late
Friday morning due to the added daytime heating maximizing MUCAPEs
upwards of 1500 J/kg some where from central Phoenix and areas to
the east of Phoenix. From late morning through mid afternoon 
Friday, models are showing the best instability and forcing to 
occur along with a fairly robust 25-35 kts of 0-6km shear. This
convective set-up is likely to result in a few hour period focused
during the early afternoon hours Friday where several strong to
severe thunderstorms are likely to impact south-central Arizona.
Model forecast soundings are supportive of strong to severe winds,
potentially some marginally severe hail, and heavy rainfall.
Guidance shows locations across central Pinal County into eastern
Maricopa County will have the best chances for seeing strong to
severe storms, but the threat may extend through the entire 
Phoenix metro into the higher terrain east of Phoenix.

The heavy rainfall threat is still expected to be more focused
across the eastern half of Pinal County, eastern Maricopa, into
Gila County where training of cells is likely to occur over a
several hour period through at least the rest of Friday afternoon.
A Flood Watch will be in effect for this area from Friday
morning through Friday evening. Rainfall amounts upwards of 1-2" 
are likely to fall in some areas with very localized higher 
amounts also possible. 

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/... 
By Saturday, the cut-off low will be quickly weakening with upper
level forcing waining while instability will be much more limited
than what is expected on Friday. Considerable cloudiness is also 
likely to affect much of the area on Saturday limiting 
destabilization. However, lingering moisture, residual weak upper
level forcing, and modest lapse rates should promote isolated to 
scattered showers and thunderstorms more so during the afternoon 
hours anywhere from southeast California into southern and central
Arizona. Additional rainfall amounts Saturday should be on the 
lighter side, but we can't rule out some very localized 0.50-0.75"
amounts due to the lingering convective potential.

Models are in good agreement the cut-off low will begin to open up
and quickly move northeast of the area during the day Sunday. 
Sunday may allow for some isolated afternoon showers and a few 
thunderstorms, but these are likely to be focused over the Arizona
high terrain. By Sunday night into Monday, our region will 
transition more into zonal to weak ridging as a deep Pacific low 
moves southward to off the Pacific Northwest coast. This will help
to usher in dry air across the region ending any rain chances 
by Sunday night. 

Temperatures will take a dive Friday into the weekend with the
help of the cut-off low and the rain cooled air. Forecast highs
this weekend are currently only in the upper 80s across the bulk
of the lower deserts, or 5-8 degrees below normal. Once we start
to see weak ridging back into our region early next week, highs
should creep up into the low to mid 90s by Monday or Tuesday. 

&&

.AVIATION...Updated at 1215Z. 

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Anticipate current light SE winds to increase by 15-16Z across the
terminals, with speeds up to 10 kts and gusts to 15-20 kts. Winds
will then veer from SE to SW late morning into the afternoon,
eventually gaining a predominant westerly component by 21-22Z,
with periodic gusts to 15-20 kts continuing. A few vicinity
showers/storms may develop in/around the Phoenix Metro by late
afternoon into the early evening, however, confidence is too low
(<30%) at this time to include in the TAFs except at KIWA. Though
confidence is low on the exact timing and strength, better
coverage of strong storms to the E/SE of the Phoenix area will
likely send an outflow and abruptly shift winds back out of the SE
between 00-04Z. If there are colliding outflows, chances for
storms will go up. Skies will remain mostly clear through the
morning until FEW-SCT cumulus clouds, with bases AOA 8 kft AGL,
develop for the afternoon and evening hours. Friday morning,
towards the end of the current TAF period, there are indications
of a lower SCT-BKN deck of clouds developing across South-Central
AZ with CIGs possibly down to 6 kft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:
At KIPL, W'rly winds are expected through the TAF period. Speeds
this will generally remain AOB 12 kts into the early afternoon. By
21-23Z anticipate gusts into the 20-25 kt range to develop, with 
a brief period (01-05Z) of gusts up near 30kt possible. 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. Speeds will
start to taper off after sunset. Skies will remain clear. 

&&

.FIRE WEATHER...
Today will bring more hot temperatures to the lower deserts, but
moisture will be on the increase. Expect isolated to scattered 
thunderstorms over the eastern districts starting this afternoon
with outflow easterly winds into the south-central Arizona lower
deserts. MinRH values will hover around 20% today across the lower
deserts before increasing Friday into Saturday with values 
upwards of 50% over the eastern districts. Friday is expected to
bring fairly widespread showers and thunderstorms across the
eastern districts with heavy rainfall likely in some areas. The 
slow-moving low pressure system impacting the region should
continue to bring chances for wetting rains on Saturday before
drying conditions begin Sunday into early next week. Below normal
temperatures are forecast for Friday through at least Monday.

&&

.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...Kuhlman
LONG TERM...Kuhlman
AVIATION...Whittock/Berislavich
FIRE WEATHER...Kuhlman