309
FXUS65 KPSR 090557
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1057 PM MST Wed Oct 8 2025

.UPDATE...Updated 06Z Aviation Discussion

&&

.KEY MESSAGES...

- High temperatures will peak in the upper 90s to 100 degrees
  across the lower deserts today. As abundant moisture arrives
  into the region, a gradual cooling trend will transpire through
  this weekend with highs falling into the low to mid 80s by
  Saturday.

- A period of active weather with multiple rounds of showers and
  embedded thunderstorms will begin on Thursday and persist into
  the weekend. Some locations could receive rainfall totals
  exceeding 2.00" which will promote excessive runoff into area
  watersheds, leading to flooding of low lying areas.

- A Flood Watch has been issued for southeast CA and southwest AZ
  from Thursday through Friday and all of southcentral AZ from
  Friday through Saturday.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...
Latest GOES-18 wv and visible satellite imagery shows Tropical Storm
Priscilla is located about 200 miles west of the southern tip of
the Baja California and continues to slowly progress N-NW. A large
plume of mid-lvl moisture extends well out ahead of the storm as
indicated by a thick cloud deck over N MX. Boundary layer moisture
is now increasing across southeast AZ where dewpoints have risen
into the mid 50s. Isolated showers and thunderstorms will be
possible through this evening mainly across the higher terrain of
SE Arizona, but a few storms could develop or move into S Gila
County or E Maricopa County. The main threat with any storm will
be a brief heavy downpour and gusty outflow winds. Deep moisture
has not quite reached southcentral AZ yet as dew points across the
lower deserts remain in the 30s and 40s. This dry air in place
and ridging aloft has resulted in temperatures topping out above
normal this afternoon. Phoenix Sky Harbor has reached 102 degrees
which may be the last 100 degree day of the year. As abundant
moisture and cloud cover moves into the region tonight,
temperatures will not cool as efficiently and only bottom out in
the mid 70s to around 80 degrees. The forecast low of 80 degrees
at Phoenix Sky Harbor Thursday morning would be a record warm
low.

Heading into tonight and early Thursday morning, we will really
start to see strong moisture advection kick into gear which will
allow for more widespread shower activity across much of the area
after midnight. The initial bands of rainfall will be light with
totals around 0.10" or less with multiple brief rounds of showers
pivoting through southcentral AZ into early Thursday afternoon. By
Thursday evening, the focus will begin to shift out west where CAMs
indicate the potential for a band of more numerous showers and
thunderstorms developing across SE California and SW Arizona. Some
of the HREF members are indicating the potential for higher rainfall
rates up to 0.75"-1.00"/hr along and west of the Colorado River
where the risk for localized flooding and flash flooding will
increase. Therefore, A Flood Watch has been issued for all of SE
California and SW Arizona starting Thursday afternoon. The band of
heavy rain will likely persist through Thursday night with the
focus slowly shifting eastward with time.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Forecast confidence remains high for a long duration, heavy rain
event lasting well into the weekend. A Flood Watch has been issued
for the entire forecast area on Friday and southcentral AZ on
Saturday. Abundant moisture from TC Priscilla will combine with
the upper level dynamics from a Pacific trough setting up to our
northwest starting late Thursday. Our biggest concern is the
amount of rainfall which may fall across south- central and
eastern Arizona with some potential for another round of rain
early next week. The lack of expected instability during the event
should limit thunderstorm development much of the time, 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.

Rain chances should increase steadily on Friday with the highest
rain chances gradually shifting from along the CO River Valley
early Friday to over south-central Arizona by Friday afternoon.
Periods of showers with some occasional embedded thunder should
affect much of the area on Friday with the rain likely
shifting away from southeast California Friday night. As the
forcing increases on Friday, we may see periods of moderate to
possibly heavy showers with embedded thunderstorms. 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 possible. Expected rainfall amounts
for Friday are likely to range from 0.25-0.50" across the majority
of the area with localized amounts upwards of an inch. WPC has a
Marginal Risk (5-10%) for localized flooding across the bulk of
the area on Friday.

The peak of the rainfall event may occur Friday night into
Saturday across Arizona with the potential mid-level remnants of
TC Priscilla moving into the area. 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 30-45 kts of mid-level southwesterly
flow for early 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. Localized rainfall rates
upwards of 0.50-1.00" per hour may be possible leading to
localized additional accumulations of an inch or so in some
locations. WPC has placed the eastern half of Arizona in a
Slight Risk for excessive rainfall on Saturday.

The latest rainfall totals through Saturday have gone down
slightly from yesterday, but we are still looking at average
amounts of around 0.5" over southeast California and 0.5-1.0"
over southwest Arizona. Higher amounts are likely to be over
central and eastern Arizona where 1-1.25" is likely across the
lower deserts to 1.0-2.0" over higher terrain areas. It is likely
some locations will see higher amounts. 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.

A second tropical system may attempt to move up Baja at some
point on Sunday into Monday. Forecast uncertainty is even higher
for this next potential weather system, but for now it may end up
affecting southeast Arizona to maybe as far north as south-
central and east-central Arizona. Our forecast still calls for a
20-40% chance for rain for Sunday-Tuesday, but it very well may be
underdone. If this next tropical system does make its way into
Sonora, we may see another round of decent rainfall early next
week. Some ensemble members show the potential for heavy rainfall
again, but given the high uncertainty it may end up being very
little.

Temperatures will cool down considerably going into the weekend
given the expansive cloudiness and expected widespread rainfall.
NBM guidance shows highs dipping below 90 degrees by Saturday
with highs anywhere from the low 80s to the upper 80s Saturday
through Tuesday.

&&

.AVIATION...Updated at 0555Z. South Central Arizona including
KPHX, KIWA, KSDL, and KDVT:
Tonight VCSH will be common at all terminals with E`rly winds
expected well into the morning. By tomorrow morning (~17Z) -SHRA
is expected at KPHX and KIWA, which can reduce visibilities to
5SM, in addition to wind speeds increasing between 10-15kts with
gusts upwards of 20kts possible. These elevated wind speeds will
linger throughout the afternoon but look to relax to aob 10kts by
near midnight tomorrow. No W`rly shift is expected tomorrow
afternoon as directions will remain out of the E to NE. FEW-BKN
clouds decks, ~100kft, will persist with this incoming activity.

Southeast California/Southwest Arizona including KIPL and KBLH:
Main aviation concern is shower activity throughout a majority of
the TAF period at both terminals. VCSH will be common through
tonight with a brief break tomorrow morning before -SHRA returns
for most of the remaining hours. Winds a KIPL will be SE`rly with
extended periods of VRB and KBLH will shift out of the NE tomorrow
morning and throughout the afternoon. FEW- BKN clouds decks,
~100kft, will persist with this incoming activity.

&&

.FIRE WEATHER...
A significant influx of moisture will progress westward through
region tonight, allowing for increasing coverage of showers and
isolated thunderstorms. The main focus for wetting rainfall will
be over western half of the forecast area Thursday afternoon and
evening before spreading into southcentral Arizona Friday and
Saturday. Winds will remain light and diurnal through tonight
before E-SE winds become established Thursday and persist through
much of the weekend. Much higher humidities will be seen starting
Thursday with MinRHs rising above 30% areawide. 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...Flood Watch from Thursday afternoon through Friday evening for
     AZZ530>533-535-536.

     Flood Watch from Friday afternoon through Saturday evening for
     AZZ534-537>563.

CA...Flood Watch from Thursday afternoon through Friday evening for
     CAZ560>570.

&&

$$

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