741 
FXUS65 KPSR 081020
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
320 AM MST Wed Oct 8 2025

.KEY MESSAGES...

- Expect slightly above normal temperatures today with lower
  desert highs generally in the mid to upper 90s.

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

- The abundant moisture and rainfall will promote cooling
  temperatures into the weekend with highs in the 80s across the 
  region starting Saturday.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...
Moisture advection into eastern Arizona has already started and
this is largely due to the expansive influence of TC Priscilla.
Southeasterly flow in the low levels and southerly flow in the
mid levels today will help to increase moisture levels throughout
the day with surface dew points increasing into the 50s east and 
southeast of Phoenix by late afternoon. The latest hi-res CAMs 
show some scattered showers and maybe a few weak thunderstorms 
developing across Gila County later this afternoon before 
additional elevated shower activity is likely to form during the 
evening hours across southern Arizona. Strong moisture advection 
during the overnight hours should allow for more widespread shower
activity across much of the area after midnight tonight, but with
somewhat limited moisture in the lower levels rainfall amounts 
should mostly be less than 0.10".

Temperatures today are likely to be the warmest of the week with
H5 heights peaking between 584-588dm. We should also see overall 
sunny skies which should lead to afternoon highs reaching into the
mid 90s across the western deserts to the upper 90s to around 100
degrees across the south-central Arizona lower deserts.
 
TC Priscilla has already started to weaken and is forecast to
continue weakening into Thursday as it continues to track just to
the west of the Baja peninsula. NHC has Priscilla nearing the
central Baja coast on Friday before becoming a remnant low as it
crosses Baja Friday night. Our main concern continues to be the
excessive moisture working its way northward into our region over
the next couple of days with guidance showing record or near
record PWATs for this time of year. 

CAMs indicate the potential for ongoing shower activity for 
Thursday morning before showers and thunderstorms may blossom 
across southeast California Thursday afternoon. There is still a 
good amount of uncertainty with the amount of instability 
available for Thursday with most of the guidance showing very 
little CAPE. However, the 06Z HRRR indicates there may be
scattered thunderstorms across southeast California. We will have
to watch for this potential as it may bring some potential for
heavy rainfall during the latter part of Thursday. Shower and
thunderstorm potential across southern and central Arizona on
Thursday looks to be lower with NBM PoPs generally between 
20-40%.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Forecast confidence remains good for a long duration rain event 
lasting well into the weekend. 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 0526Z. 

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected during the TAF period. Typical
diurnal tendencies will continue through tonight before a S'rly
shift tomorrow afternoon instead of the typical W'rly direction.
Wind speeds will mostly be aob 10kts. FEW mid-level clouds will be
common through the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during he TAF period. Winds 
will continue to favor diurnal trends with extended periods of VRB
to even calm conditions. Clear will persist through Wednesday 
morning, where then FEW mid-level clouds will develop Wednesday 
afternoon.

&&

.FIRE WEATHER...
Today will again bring overall dry conditions for much of the
area, but moisture will be increasing across Arizona allowing for
some isolated showers and thunderstorms over the eastern Arizona
high terrain by this afternoon. Starting Thursday, abundant
moisture over the entire area will lead to increased rain chances.
Winds today will remain light following diurnal trends before
easterly winds take over for the whole day on Thursday. MinRHs 
today across the lower deserts will bottom out around 15% with 
values closer to 30% in Gila County. Much higher humidities will 
be seen starting Thursday with MinRHs above 30% areawide. There 
will be chances for wetting rainfall from Thursday through at 
least Saturday with some potential for heavy rainfall. 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...Ryan
FIRE WEATHER...Kuhlman