636
FXUS65 KPSR 082310
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Mon Sep 8 2025

.UPDATE...Updated 00Z Aviation Discussion.

&&

.KEY MESSAGES...

- A few isolated showers and thunderstorms over prominent terrain
  features of Southwest and South Central Arizona cannot be ruled
  out this afternoon.

- Overall dry conditions are expected for the next 7 days with
  only slight chances for rain over the eastern Arizona high
  terrain late Wednesday into Thursday.

- Temperatures will stay within the normal range into mid week,
  resulting in locally Moderate Heat Risk for the lower deserts,
  before cooling slightly late week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
A broad area of negative midlevel height anomalies has begun to push
into the Western CONUS, with its center currently just off the
NorCal Coast. Meanwhile, the region remains under the influence of a
subtropical high now centered just west of Baja California. Modest
west/southwest flow aloft between these synoptic features continues
to modify moisture profiles, with a sharp decrease in dewpoints
above ~600 mb evident in 12Z soundings from both Phoenix and Yuma
(slightly drier out west, with the sharp vertical dewpoint gradient
present at a lower altitude in Yuma). However, lingering low level
moisture made for a warmer than normal and rather humid morning
across South-Central and Southwest AZ, with widespread surface
dewpoints in the middle 60s and even some spots in the lower 70s
such as the Yuma area. Objective analysis also showed mean near-
surface (1000-700 mb layer) mixing ratios between 11-13 g/kg across
a rather broad area. Once again, this should be sufficient to
support isolated showers and perhaps a few thunderstorms over
prominent terrain features. Chances for showers/storms across the
area are generally 10% or less except over the mountains south of I-
8 between Gila Bend and Casa Grande, where chances are closer to
20%. As dry air continues to mix down into the boundary layer, rain
chances will fall below 5% by Tuesday, even over higher terrain.

Temperatures today and Tuesday have trended upwards another degree
or so and are now forecast to reach 102-106F across the lower
deserts, the warmest forecast values of the next 7 days according to
the latest NBM. These high temps are not far from daily normals for
the time of year, however, this translates to widespread Minor and
locally Moderate HeatRisk for the typically hotter lower desert
locales.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
The Pacific low to our northwest will begin to expand and push
inland Tuesday into Wednesday with the low center stalling out
across northern California. The southeastern fringes of the larger
scale trough will eventually spread over our region by Wednesday
causing noticeable height falls. This will drive an increase in
winds by Wednesday with much of the area seeing afternoon wind
gusts to around 25 mph. Temperatures will also begin to lower on
Wednesday, more so across southeast California and southwest
Arizona where highs should drop to below 100 degrees.

As the trough gradually spreads over our region, southerly flow
will also increase briefly advecting some moisture northward into
eastern Arizona. PWATs will still be on the lower side at around
1.0", but with some weak upper level forcing moving into the area
it may be enough for some low end rain chances across the eastern
Arizona high terrain Wednesday night into Thursday.

Ensemble guidance is in fairly good agreement showing the low
center sagging farther to the south into the southern half of
California and/or into southern Nevada late Thursday before
lifting back to the northeast on Friday. This should bring even
lower heights over our region by Friday likely resulting in our
`coolest` day of the week with highs in the mid to upper 90s
across the lower deserts. Broad troughing is then expected to
somewhat stay over our region through the weekend and possibly
longer with a second Pacific low developing off the California
coast next weekend. This pattern should keep temperatures from
rising much next weekend with the latest NBM forecast highs
showing readings mostly in the upper 90s to around 100 degrees.
Guidance also shows even drier air filtering through the entire
area by next weekend pushing PWATs to as low as 0.5", or around
50% of normal for the period.

&&

.AVIATION...Updated at 2310Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will favor the W through the rest of today with winds
becoming light and variable at KSDL and KDVT by this evening.
Winds will switch around to the east overnight tonight (~06Z at
KIWA and ~10Z at KPHX). Wind speeds through/shortly after sunset
will mostly stay between 5-10 kts, with a few breezes into the
teens. SKies during the daytime hours will have FEW CU with bases
around 7-8 kft, but clear skies are expected during the night and
early morning hours.

Southeast California/Southwest Arizona including KIPL and KBLH:
No significant aviation weather concerns are expected over the
next 24 hours under mostly clear skies. Winds will remain
predominantly westerly at KIPL and southwesterly at KBLH with
speeds mostly between 5-10 kts. A brief period of gusty sundowner
winds is expected at KIPL this evening, with gusts up to 20-25 kts
between 01-05Z. KBLH may have a few occasional gusts into the mid-
teens through/shortly after sunset.

&&

.FIRE WEATHER...
Conditions will continue dry out, with slight rain and
thunderstorm chances over higher terrain areas this afternoon
(generally 10-15% or less over some isolated spots) falling to
near zero by Tuesday. Humidity will also decrease, with minRHs of
20-30% this afternoon falling to 15-25% Tuesday onward. A low
pressure system will approach the region and remain to the
northwest mid week, bringing increased afternoon and evening
breeziness. Gusts to 20-25 mph will become common with this,
particularly on Wednesday and Thursday. Chances for wetting rains
briefly return Thursday, when the eastern Arizona high terrain
may see isolated to scattered showers and thunderstorms. Near
normal temperatures today and Tuesday will cool to slightly below
normal during the latter half of the week thanks to the incoming
low pressure system.

&&

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

$$

SHORT TERM...Whittock
LONG TERM...Kuhlman
AVIATION...Berislavich/Smith/Benedict
FIRE WEATHER...Whittock

NWS Phoenix Office