682
FXUS65 KPSR 061710
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1010 AM MST Mon Oct 6 2025

.UPDATE...Updated 18Z Aviation Discussion.

&&

.KEY MESSAGES...

- Temperatures will warm over the next few days reaching slightly
  above normal levels across south-central Arizona starting
  Tuesday. Highs across the lower deserts should peak on Wednesday
  and Thursday reaching into the mid to upper 90s.

- A period of active weather seems very possible 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.

- Cooler temperatures are forecast by next weekend with highs
  likely dropping to below normal by Sunday.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Very little has changed over the past 24 hours with dry
southwesterly flow still in place across the Desert Southwest. A
very weak trough is still positioned just off the California
coast, while TC Priscilla continues to strengthen off the west
coast of central Mexico. The main change we will see over the next
couple of days will be an increasing influence from the
subtropical ridge which is currently centered over the Southern
Plains. The ridge is forecast to gradually strengthen into the
middle part of the week while nudging more into our region.
Temperatures will begin to respond today to the increasing heights
as readings warm into the lower 90s. The warming will continue
Tuesday into Wednesday with highs Wednesday reaching into the mid
90s across southeast California to near 100 degrees across south-
central Arizona.

Wednesday will also mark the beginning of a drastic increase in
moisture across the region. The first bout of moisture is slated
to shift out of northeast Mexico and New Mexico as the mid level
flow turns southeasterly partially in response to TC Priscilla
getting closer to southern Baja. 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. As TC
Priscilla is expected to continue to move farther to the north off
the coast of Baja Wednesday night into Thursday, the moisture
advection will really kick into gear.

&&

.LONG TERM /WEDNESDAY 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
by 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
during the period reaching above normal by Tuesday. Expect the
light winds to continue, generally following diurnal patterns.
Daily MinRHs of 10-15% will also persist, with overnight
recoveries of 30-50%. Starting Thursday, we are likely to see the
beginning on an 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%.

&&

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

$$

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