168
FXUS65 KPSR 062051
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
151 PM MST Mon Oct 6 2025

.KEY MESSAGES...

- Temperatures will warm slightly above normal across south-central
  Arizona starting Tuesday. Highs across the lower deserts should
  peak on Wednesday reaching into the upper 90s to around 100
  degrees.

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

- A period of active weather is likely starting as early as Thursday
  and lasting through the weekend. An influx of tropical moisture
  into the area may lead to localized heavy rainfall and flooding
  potential.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a
ridge of high pressure centered over northern MX and and south TX
while a weak cutoff low pressure system is situated just off the
coast of CA. Between both of these features, dry southwesterly flow
prevails over the Desert Southwest allowing for clear skies and
temperatures hovering around normal values this afternoon. Hurricane
Priscilla is located about 100 miles south of the lower tip of the
Baja California and continues to remain at Cat 1 strength. This
storm is forecast to track slowly N-NW over the next few days and
eventually weaken as it remains just west of the Baja California.
The remnant moisture from Priscilla will eventually arrive later
this week, providing a focus for a prolonged rainfall event across
the Desert Southwest.

Through at least the first half of the week our region will remain
under the influence of the subtropical ridge. The ridge is forecast
to gradually strengthen into the middle part of the week which will
result in an overall increase in hghts aloft, especially over the
eastern half of the forecast area. In response, temperatures will
gradually increase over the next couple of days from the mid to
upper 90s on Tuesday to the upper 90s to around 100 degrees on
Wednesday. These lower desert highs are around 5 to 7 degrees
above normal for this time of year. Tropical moisture from
Priscilla will begin to arrive in southeastern AZ throughout the
day on Wednesday. Portions of southern and eastern Arizona will
likely see some increased clouds later in the day Wednesday, while
surface dew points increase from the low to mid 30s to upwards of
50 degrees across southeast Arizona. Moisture advection will
continue to progress into the state heading into Wednesday night
which will allow for warmer low temperatures across our region on
Thursday morning.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The main forecast concern later this week and through the weekend
will be the potential for several rounds of rainfall which could
lead to localized flooding in some areas. High model spread still
remains resulting in a low confidence forecast, but the threat for
impactful rainfall is a possibility.

As mentioned earlier, strong moisture advection is likely to
occur early Thursday mostly driven by TC Priscilla making its way
northward off the coast of Baja. Both the GEFS and the EPS mean
PWATs quickly rise on Thursday reaching anywhere from 1.4-1.8" by
Thursday evening, or 200-300% of normal for this time of year. It
seems quite possible the moisture will be spread across much of
the entire atmospheric column with forecast soundings becoming
nearly saturated from 750mb to just above 300mb. This abnormally
high amount of moisture will likely be a deterrent for convective
development with very little in the way of instability presenting
itself due to warmer air aloft and considerable cloudiness that is
likely to form. That does not mean we will not have rain chances
beginning Thursday, but we will have to rely more on dynamical
forcing instead of our typical instability induced convection.
The most likely forcing mechanisms that will help to drive
precipitation chances starting Thursday should come from the
southwesterly moist isentropic forced ascent and from broad upper
level jet forcing. This far out with the amount of model
uncertainty, the jet forcing is still more of a wild card as the
timing and exact jet placement is still fairly uncertain. Rain
chances Thursday may start as early as the afternoon, but that may
be a bit early as the best forcing is likely to occur later in
the event as the trough enters the region.

TC Priscilla should eventually dissipate somewhere off the coast
of central or northern Baja by around Friday or Saturday with at
most some residual mid or upper level vorticity making its way
into our region. The more likely bigger concern for our area will
be the potential impact of the tropical moisture interacting with
the increasing mid-level flow Friday into Saturday. Models show
the potential for quite strong upslope flow into central Arizona
later Friday into Saturday which may pose threat for a decent
amount of rainfall to fall into the higher terrain of Arizona.
Models also eventually show another jet max strengthening over the
Great Basin over the weekend will could provide for another round
of good upper level forcing. There are still a good number of
things that may change over the coming days with the evolution of
this weather event, but it seems possible some areas may see more
than an inch or two of rainfall. For now, it look like the peak
of the event may occur on Friday and/or Saturday with residual
rain chances potentially lasting into early next week across
portions of Arizona. Over the next few days, we hope to have a
better idea on the details of this coming rain event.

&&

.AVIATION...Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will tend to follow their typical diurnal tendencies with
extended periods of light and variable to calm winds. Skies will
remain clear.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will generally be light and variable with periods of calm
winds through the TAF period. Skies will remain clear.

&&

.FIRE WEATHER...
Dry conditions with clear skies and no chances for rain are
expected through Wednesday. Temperatures will gradually warm
through the middle of this week reaching above normal on Tuesday,
and peaking on Wednesday. Expect the light winds to continue
across the lower elevations with some enhanced afternoon
breeziness across the higher terrain. Daily MinRHs of 10-15%
will also persist through Wednesday, with overnight recoveries of
30-50% region-wide. On Thursday, we are likely to see a shift to
a more active period of weather with moisture quickly increasing
across the region. There will be chances for wetting rainfall by
late Thursday and likely carrying through the weekend. 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...Salerno
LONG TERM...Kuhlman
AVIATION...Berislavich
FIRE WEATHER...Kuhlman/Salerno