756
FXUS65 KPSR 171140
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
440 AM MST Wed Sep 17 2025

.UPDATE...Updated 12z Aviation Discussion...

&&

.KEY MESSAGES...

- Rain chances will increase today into Thursday with the best
  chances for showers and thunderstorms across southeast
  California and southwest Arizona on Thursday.

- Thursday will also bring the potential for heavy rainfall and
  minor flooding with the best chances across southwest Arizona.

- Lingering chances for showers and a few thunderstorms will be
  possible on Friday focused more across the Arizona high terrain.

- Temperatures are will fall below normal by Thursday before
  quickly rising over the weekend into early next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
The main forecast concern over the next 2-3 days will be the
potential for thunderstorms producing heavy rainfall which could
create some localized flooding issues. Forecast uncertainty is
still higher than normal, but with the dramatic increase in
moisture we will see over the next 24-36 hours it will at least
bring some chances for heavy rainfall.

TC Mario has transitioned into a remnant low, but it continues to
help to advect moisture northward with some of it already reaching
far southern California and southern Arizona. PWATs across our
area are still only between 1.0-1.3" over the bulk of the lower
deserts, but they now have reached as high as 1.5-1.7" over Yuma.
Richer moisture just to our south is forecast to advect northward
up the Lower CO River Valley today and then spread outward with
PWATs of 1.5-1.8" likely over much of our area by late this
evening.

Rain chances will start to pick up later this afternoon,
especially across southeast California and southwest Arizona where
some scattered showers and maybe a few isolated thunderstorms are
expected. The lack of strong instability and relatively low DCAPEs
means the threat for any strong storms will be fairly low today,
while the risk of heavy rainfall also remains on the low side. A
wing of vorticity is then forecast to move from south to north
across the area Thursday morning likely sparking off some
additional showers and isolated thunderstorms. CAMs show this
activity likely being focused more across southwest Arizona.

Thursday is still looking like the most active weather day of this
week as we reach peak moisture levels in the morning and upper
level support is expected to be at its highest. However, model
uncertainty remains fairly high as CAMs have been in constant
disagreement on the amount of convection. Model runs from 18Z and
00Z yesterday had backed off on the potential convection for
Thursday and this has filtered into the NBM PoPs lowering again,
but the 06Z HRRR has just come in looking very optimistic for
storms on Thursday. The best chances for showers and thunderstorms
still looks to favor southeast California and southwest Arizona
on Thursday with PoPs of 40-60%, while areas to the east in
Arizona are mostly between 20-40%. The 06Z HRRR also shows the
potential for nearly stationary or back building storms (focused
over La Paz into southern Maricopa Counties) which means the
potential for heavy rainfall and flooding will definitely be
present.

The rainfall event Thursday is likely going to fall under a
scenario where a few localized spots see heavy rainfall of 1-2", a
bit larger area sees amounts of 0.25-0.75" and about half of the
area see little to no rainfall. WPC has maintained their Marginal
Risk on the DAY 2 Excessive Rainfall Outlook, but they have
mentioned the potential for upgrading to a Slight Risk for a
portion of the area. As additional Hi-res model runs come in, we
should have a better idea on the heavy rainfall potential later
today into tonight.

By Thursday night into Friday, guidance has been consistent in
showing considerable dry air advecting southwest to northeast
across the region. This is expected to happen as the trough to our
west lifts to the north northeast into central California and
Nevada. Given our residual good moisture within the low and mid
levels on Friday, we are still likely to see some scattered
showers and maybe some isolated thunderstorms but much of the
activity is likely to be focused over higher terrain locations.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As we continue to dry out Saturday into Sunday, rain chances will
essentially come to an end with very minimal 10% chances for a
shower or weak storm over higher terrain locations. Forecast PWATs
are shown to drop to between 1.2-1.4" by Saturday afternoon and
closer to 1" for much of the area on Sunday. Our region will also
see the subtropical ridge centered to our south shift more over
our region with H5 heights rising to between 590-592dm again.
The near normal temperatures that are expected on Thursday and
Friday will quickly trend higher beginning this weekend with highs
likely reaching 100 degrees Saturday and 101-104 degrees Sunday.
Moderate HeatRisk is also expected to make a return this weekend
across the lower deserts.

Model guidance is starting to point toward even hotter
temperatures during the first half of next week as a potential
second Pacific trough is likely to stay far enough to our west to
allow the subtropical ridge to fully move over our region by
Monday or Tuesday. If this happens, we very well could see H5
heights increase to around 594dm, or nearing climatological
records for the period. The latest NBM forecast highs show
readings topping out near 105 degrees by Monday before peaking
between 105-108 degrees on Tuesday and/or Wednesday of next week
(right near daily records). We can`t even rule out the potential
for reaching 110 degrees in a few spots.

&&

.AVIATION...Updated at 1135Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected throughout the TAF
period. The overall wind pattern will exhibit the familiar diurnal
tendencies with speeds generally aob 10 kts. SCT to occasionally
BKN clouds above 10 kft will be common throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
At KIPL, winds will generally be out of the southeast through this
afternoon before temporarily changing to a more westerly component
early this evening. At KBLH, winds will generally fluctuate
between the south to southwest. The overall wind speeds will
generally remain aob 10 kts. There is about 15-30% chance of some
afternoon SHRA with highest chances near KIPL, however, confidence
of occurrence is low at this time so left out the mention of VCSH
for this TAF package. If SHRA or TSRA activity does materialize,
then some gusty and erratic winds will be possible. SCT to BKN
clouds aoa 10 kft will be common throughout the period.

&&

.FIRE WEATHER...
Above average temperatures will continue today before cooling off
slightly late week with increased cloud cover and rain chances.
Rain chances will begin today mainly over the western districts
before peaking on Thursday areawide. Chances of wetting rains on
Thursday range from 30-50% over the western districts to 20-30%
over eastern districts. MinRHs will continue to improve into
Thursday mostly staying above 25-30% into Saturday. Outside of any
storms, will remain light over the next few days with directions
mostly following diurnal trends. High pressure will settle back
into the region over the weekend and through much of next week
resulting in a warming and drying trend.

&&

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

$$

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