605
FXUS65 KPSR 242320
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Sun Aug 24 2025

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Moderate to major HeatRisk with Extreme Heat Warnings remaining in
effect for much of the lower deserts today.

- Widespread showers and storms are expected on Monday and possibly
Tuesday with some storms being strong along with the potential for
localized heavy rainfall and flooding.

- Temperatures cool to below normal starting Tuesday.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...
For the rest of today, moisture looks to remain marginally
supportive of a few strong storms within the CWA with isolated to
scattered development expected initially over prominent terrain
features between Phoenix and Yuma (better coverage over Western Pima
County, where several strong thunderstorms have already been
observed early this afternoon). RAP analyzed PWATS are generally
between 1.2-1.5" across Southwest AZ, though a layer of midlevel dry
air is still apparent in Yuma GFS bufr soundings for this afternoon,
which would act to inhibit convective potential. With the
subtropical high centered south of the Four Corners, southeasterly
steering flow will exist today of ~20 kts, acting to push activity
from Western Pima County into Southern Maricopa and Eastern Yuma
County, where DCAPE values are in excess of 1500 J/kg. This presents
perhaps the best opportunity for strong to marginally severe wind
gusts today if storms survive into the lower elevations, also
presenting a concern for blowing dust.

A few large scale features evident in current midlevel wv imagery
and 500 mb RAP analysis will be key players in determining how
active our weather gets on Monday: an inverted trough in the Gulf of
California near the tip of Southern Sonora, and a larger upper level
trough with attendant jet max along its southern flank approaching
the CA Coast. Overnight, the inverted trough or remnants of it are
depicted by global guidance rotating anticyclonically about the
subtropical high and into the Western CWA. Moisture will increase as
this occurs, with ensemble mean PWATS reaching 1.5-1.7".

Most CAMs show showers with embedded thunderstorms blossoming early
Monday morning over Southwest AZ with this moisture and elevated
instability being imported over the area. Simultaneously, the upper
trough off the CA Coast draws near, gradually cooling temperatures
aloft (steepening lapse rates). The jet max at its southern flank
shows a pronounced diffluent signature as it moves over the region,
further supporting the uncapped and favorable environment for storms
to form later in the day. One limiting factor for storm formation
will be lingering cloud cover over Southwest AZ into Southeast CA
from the aforementioned morning showers/storms, however once they
clear the area, destabilization may be rather rapid, and areas not
clouded over stand a good chance of producing strong thunderstorms.

Localized flash flooding remains a concern for Monday, particularly
with thunderstorms that form in the mid to late afternoon over SE CA
and SW AZ; model soundings show midlevel RHs in excess of 70%, and
LCLs well below the freezing level, so efficient warm rain processes
and strong updrafts can produce heavy rainfall - a few spots
potentially seeing between 1-2" of rain. Farther to the east across
south-central and eastern Arizona, instability and upper level
support is likely to be less supporting weaker storms but still
fairly widespread coverage of rainfall. PoPs on Monday remain quite
high at 50-70% over the bulk of the area.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Assuming Monday is quite active across the area with most areas
seeing showers and/or thunderstorms, Tuesday is likely to see
decreased chances of thunderstorms. Moisture is still likely to be
quite plentiful through much of Tuesday and colder air aloft from
the Pacific trough should spread eastward across the area. However,
the upper levels are likely to be less supportive with a jet max
nosing into southern California. The current forecast thinking for
Tuesday is the area of best rainfall potential is likely to shift
more over central and northern Arizona with decreasing chances
across California. Rainfall amounts on average are likely to be on
the lighter side, but we can`t rule out some localized areas seeing
upwards of an inch or so.

Starting Tuesday night, we should begin to see drier southwesterly
flow set up over our area, eventually pushing out any remaining
moisture by Friday. Forecast PWATs are shown to drop to between 1.2-
1.4" by Wednesday afternoon and 1.0-1.2" by Thursday afternoon. As a
result, rain chances will quickly lower starting Wednesday with PoPs
falling to between 20-30% before dropping to 10% or less starting
Thursday. This period of dry conditions should last through at least
next weekend.

Temperatures for the coming week will drop quickly early in the week
as moisture and cloud cover increases. By Tuesday, highs are likely
to drop to around 100 degrees across the lower deserts and stay
there again for Wednesday. As conditions dry out later this week,
highs are expected to slowly creep back toward normal readings while
overnight lows stay fairly comfortable in the 70s for most places.

&&

.AVIATION...Updated at 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Fairly low confidence forecast through Monday evening given large
uncertainty with respect to thunderstorm development, evolution, and
effects on winds and operations. Evidence of an organized W/NW
outflow with evening is too low to continue mention in this TAF
package, rather a more likely outcome being a slower, partially
stalling outflow boundary with lesser impacts to operations. Winds
may never complete a true easterly switch late tonight, and
confidence is moderate that directions will quickly revert back to
W/SW late Monday morning.

The potential exists for much greater operational impacts Monday
evening depending on proximity of thunderstorm formation and
movement. Modeling suggests a more organized, gusty outflows from
the south becoming dominant Monday evening, but may also be
accompanied by another easterly outflow which could conceivably
initiate TSRA within the terminal footprints. Updated forecasts may
need more direct TSRA mention and associated impacts.



Southeast California/Southwest Arizona including KIPL and KBLH:
SHRA/TSRA with gusty, erratic winds will be a hazard to operations
through Monday evening under periods of mid/high cigs mostly above
8K ft AGL. Confidence is good that TS west of KIPL late this
afternoon should gradually dissipate with outflow winds weakening
and vsby quickly improving. Another similar round of TSRA appears
likely Monday afternoon. SHRA/TSRA should approach KBLH late
tonight/Monday morning with good confidence of prolonged, periodic
SHRA into early Monday afternoon.

&&

.FIRE WEATHER...
Above normal temperatures today will quickly cool Monday into
Tuesday as moisture and rain chances increase. Thunderstorm chances
are likely to be focused more across southwest Arizona today before
expanding into southeast California and south-central Arizona on
Monday with strong gusty winds being a concern. Wetting rain chances
will also increase to between 30-50% areawide for Monday and Tuesday
with localized heavy rainfall possible. Afternoon MinRHs will
continue to improve from around 20% today to 30% by Tuesday. Drying
conditions are then expected later this week with rain chances
mostly coming to an end by Thursday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ530>555-
     559.

CA...Extreme Heat Warning until 8 PM PDT this evening for CAZ560>570.

&&

$$

SHORT TERM...Whittock
LONG TERM...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman

NWS Phoenix Office