605
FXUS65 KPSR 071729
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1029 AM MST Tue Oct 7 2025

.UPDATE...Updated Aviation Discussion

&&

.KEY MESSAGES...

- Near to slightly above normal temperatures are expected through
  mid week with peak highs of near 100 degrees across the south-
  central Arizona lower deserts on Wednesday.

- Cooler temperatures are forecast to arrive late this week,
  falling below normal across the region by Saturday.

- A period of active weather with daily chances for showers and
  isolated thunderstorms will begin by Thursday and last into the
  weekend. An influx of tropical moisture into the area may lead
  to localized heavy rainfall and flooding potential.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Today and Wednesday will be our last quiet days of the week before
record moisture for this time of year (associated with TC
Priscilla) moves into the region from the south. For the moment,
our region is still caught between a weak upper level trough to
the west and the subtropical ridge to the east. Heights aloft
continue to creep upward across eastern portions of the region due
to the influence of the ridge and this will push daytime highs
well into the 90s today and Wednesday across south-central
Arizona. We may even see readings reach 100 degrees within the
Phoenix metro on Wednesday.

Moisture levels will stay stable for much of today with PWATs
between 50-80% of normals and surface dew points in the 30s.
However, this will quickly change starting Wednesday as moisture
situated to our east and southeast will begin to advect into
eastern Arizona. By Wednesday afternoon, guidance shows PWATs
nearing 1.25" across southeast Arizona (200% of normal). The flow
pattern will quickly adjust from out of the southwest today to
the southeast on Wednesday as TC Priscilla charges north
northwestward off the coast of southern Baja. The increasing
moisture on Wednesday should also allow for some isolated showers
and thunderstorms to develop by the afternoon hours across the
eastern Arizona high terrain. Given the still somewhat drier air
in the lower levels, we may even see outflow winds from this
activity reaching into the south-central Arizona lower deserts
early Wednesday evening.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Forecast confidence is increasing in a long duration rain event
starting Thursday and lasting through at least Saturday. The main
drivers of this upcoming active period of weather will be the
record moisture from TC Priscilla advecting into our region for
Thursday through Saturday and the upper level dynamics from a
Pacific trough setting up to our northwest starting late Thursday.
Over the past 24 hours, models have trended even wetter while the
track of Priscilla has turned more to the east by Friday. Our
biggest concern is the amount of rainfall locations across south-
central and eastern Arizona will receive over the 2-3 day period.
The lack of expected instability during the event will likely
hinder thunderstorm development, but the amount of moisture and
the persistent forcing are expected to lead to intermittent
periods of at least moderate rainfall which may eventually lead
to flooding issues in some areas.

Strong moisture advection will continue Wednesday night into
Thursday with PWATs of 1.5-1.9" spreading over the entirety of the
lower deserts by Thursday afternoon. This amount of moisture for
the second week of October is basically unprecedented with
guidance showing a large area of record high PWATs stretching from
the Lower CO River Valley through the majority of Arizona.
Because moisture is expected to be throughout the entire
atmospheric column, lapse rates will be very marginal resulting in
MUCAPEs mostly below 500 J/kg. Since instability and DCAPEs will
be very limited, the chances of seeing strong storms should be
small. However, given 0-6km shear will be on the higher side for
much of the event we can`t completely rule out a few rotating
discrete storms that could produce some very localized strong
winds.

Rain chances should increase steadily Thursday into Friday with
the highest rain chances falling on Friday and Saturday. Showers
with some occasional embedded thunder should start off by Thursday
morning focused more to the north of the Phoenix area
southwestward into southeast California and southwest Arizona. Jet
forced dynamics along with weak to moderate southerly mid-level
upslope flow will help to drive the rain activity on Thursday. For
now, QPF amounts on Thursday are likely to stay on the lighter
side, but we can`t rule out some localized amounts upwards of
0.5".

For Friday, we are likely to see a bit stronger jet forced and
upslope ascent with periods of moderate to possibly heavy showers
and embedded thunder. The best potential for persistent training
of activity is likely to be over south-central Arizona with a
focus in the foothills and mountain areas north and northeast of
Phoenix. Friday`s rain activity should easily be enough to get
washes flowing in many areas with some low-land minor flooding
also possible. Expected rainfall amounts for Friday are likely to
range from 0.25-0.50" across southeast California and southwest
Arizona to 0.5-0.75" across much of south-central Arizona. This
also places the bulk of the area in a Marginal Risk (5-10%) for
localized flooding.

Guidance currently shows the peak of the rainfall event is likely
to occur Friday night and Saturday with the potential mid-level
remnants of TC Priscilla passing through portions of our region.
This timeframe should also match up with stronger mid-level
upslope flow as the Pacific trough to our northwest moves onshore
into northern California and Nevada. Models show a strong
35-50kts of mid-level southwesterly flow for Saturday centered
over central Arizona. The combination of this impressive upslope
forcing and the continuation of the upper level dynamics may allow
for a band of moderate to heavy rainfall to form across the area,
likely focused across central Arizona. Localized rainfall rates
upwards of 0.50-1.00" per hour may occur on Saturday leading to
localized additional accumulations of 1-2". WPC has placed much of
central and northern Arizona in a Slight Risk for excessive
rainfall on Saturday.

Predicting the amount of rainfall for Thursday through Saturday
is not easy, but models are definitely showing impressive amounts
for much of Arizona. The latest guidance shows average amounts of
up to 0.5" over southeast California and 0.5-1.0" over southwest
Arizona. The highest amounts are likely to be over central and
eastern Arizona where 1-1.5" is likely across the lower deserts to
1.5-2.5" over higher terrain areas. These are just the average
expected rainfall amounts through Saturday and it`s quite likely
some locations will see higher amounts. In fact for Phoenix, there
are roughly 30% of the GEFS members and 20% of the EPS members
showing greater than 2" of rainfall. Given much of this rainfall
is likely to be spread out over a couple of days, urban flooding
is not expected. However, it seems quite likely washes and small
streams/creeks will see some decent flow with some flooding
possible.

The rain for some areas is not likely to be over after Saturday
as the Pacific trough to our north northwest will stick around and
a second tropical system may attempt to move up Baja at some point
on Sunday into early next week. Forecast uncertainty is even
higher for this next potential weather system, but for now its
more likely to affect southeast Arizona to maybe as far north as
south-central and east-central Arizona. Our forecast does put a
20-40% chance for rain on Sunday and Monday, but it could be
underdone depending on what happens with the next tropical system.
Guidance does show potential for another 0.5-1.0" of rainfall for
portions of our area on Sunday and Monday, but as stated earlier
uncertainty is quite high.

Temperatures are mostly an afterthought given the potential for
impactful rainfall later this week. Guidance has definitely
trended cooler given the higher likelihood of widespread rainfall.
NBM forecast highs are now only in the lower 90s by Thursday with
at least the western deserts down into the 80s starting Friday.
By Saturday, the entire lower deserts should be well into the 80s
for highs, or at least 5 degrees below normals. Highs very well
could average in the mid 80s through early next week depending on
what happens with the second potential tropical system.

&&

.AVIATION...Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected during the TAF period. Diurnal
trends will continue with windows of VRB to even calm conditions.
Clear skies will prevail through tonight before FEW mid-level
clouds start to filter in over the region.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected over the next 24 hours. Winds
will continue to favor diurnal trends with extended periods of VRB
to even cal conditions. Clear will persist through Wednesday
morning.

&&

.FIRE WEATHER...
Dry conditions with clear skies and no rain chances are expected
today with only minimal chances for an isolated shower or
thunderstorm across Gila County on Wednesday. Temperatures will be
near to slightly above normal through Wednesday. Expect light and
diurnal winds to continue across the lower elevations with some
afternoon upslope gusts around 20-25 mph across the higher terrain
of southcentral AZ. Minimum humidity will bottom out around
10-15% today before improving quickly from east to west Wednesday
into Thursday. On Thursday, we are likely to see a shift to a
more active period of weather with abundant moisture helping to
bring shower and thunderstorm chances to the area. There will be
chances for wetting rainfall from Thursday through at least
Saturday. There is also some potential for heavy rainfall during
this time, but forecast uncertainty remains high. MinRHs will at
least increase into the 20-30% range by Thursday and likely higher
by the weekend with overnight recoveries of 45-65%. Due to the
increase in moisture and rain chances, temperatures will gradually
cool from near normal to below normal by this weekend.

&&

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

$$

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