801
FXUS65 KPSR 042300
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
400 PM MST Fri Sep 4 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- Residual moisture may spark a few showers and storms this
afternoon, mainly south and east of Phoenix.

- The moisture axis and corresponding rain chances will shift west
into southeast California and southwest Arizona during the weekend.

- Temperatures will remain near to slightly below normal through
this weekend before warming to slightly above normal by early next
week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...
The overall synoptic pattern continues to be defined by an elongated
ridge of high pressure extending from the Southern Plains into the
southeastern U.S. while a broad trough encompasses much of the
Pacific Northwest and west coast. Due to this pattern configuration,
the Desert Southwest remains under dry southwesterly flow aloft.
Residual low-level moisture from Hurricane Marie, centered well to
the west of the southern tip of the Baja Peninsula, remains across
much south-central and southeast AZ with dewpoints in the 60s while
much drier air with dewpoints in the 30s and 40s encompasses much of
southeast CA and southwest AZ. The residual moisture will still
combine with strong daytime heating to cause cumulus buildups
heading into this afternoon across south-central AZ with the
potential for a few showers and storms to develop, mainly across the
terrain escarpments. However, as the afternoon progresses, drier air
will be filtering in from the west, which will erode the low-level
moisture somewhat and thus reduce instability significantly with the
latest forecast soundings from Phoenix showing CAPE values dropping
from over 1000 J/KG earlier today to less than 100-200 J/KG by this
afternoon. Therefore, any convective cells that attempt to develop
this afternoon will be very short-lived.

As Hurricane Marie continues to move northwestward well offshore
from the Baja Peninsula over the weekend, some additional moisture
will be transported northward but this time towards southern CA and
southwest AZ as PWATs rise to around 1.6-1.8". Therefore, rain
chances heading into this weekend will be mainly confined across
these areas with PoPs only topping out between 10-20%. An abundance
of mid to upper-level moisture will result in extensive mid-high
clouds across much of the area so as a result mid-level lapse rates
and thus instability will be very poor with forecast soundings
showing little to no CAPE. As a result, any rainfall activity that
materializes will be on the light side with little to no impacts. In
fact, much of the activity that falls on Saturday across southeast
CA and southwest AZ may actually be virga given that the low- levels
will remain very dry as dewpoints will still be in the 30s and 40s.
Better low-level moisture is expected heading into Sunday, however,
the better forcing for ascent from an upper- level jet streak is
likely to shift northward towards the Mohave Desert Region, where
the best rain chances will be located. Fairly quiet weather is
expected this weekend across much of south- central AZ as the lack
of instability and forcing for ascent will hinder storm activity.

The continued presence of troughing to our west will continue to
maintain temperatures near to slightly below normal levels through
the weekend with highs generally in the upper 90s to low 100s, with
Saturday expected to be the coolest day. In fact, due to the
presence of abundant mid to high clouds across much of the western
deserts on Saturday, temperatures may struggle to reach the triple
digits. The associated height falls from the troughing to our west
will also result in another round of afternoon/early evening
breeziness today across much of southeast CA and southwest AZ with
peak gusts around 20-30 mph, potentially reaching up to 40 mph in
the typical wind prone areas of far southwest Imperial County.
Slightly weaker winds are anticipated during the weekend.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Deterministic and ensemble guidance continue to differ on the
magnitude and positioning of the subtropical ridge early next week
which will dictate how hot temperatures get and how soon rain
chances will return to our area. Both the EPS and GEFS show the
ridge strengthening over the Southern Plains through the middle of
the week which will allow hghts aloft to increase across much of the
Desert Southwest. In turn, temperatures will also increase from near
normal Monday to slightly above normal on Tuesday. The temperature
forecast becomes much more unclear heading into the middle of next
week with large spreads in the NBM interquartile range. This is
likely due to differences in the magnitude of the ridge with many
EPS members showing a stronger ridge with 500 mb hghts approaching
596-598 dam while the GEFS shows slightly lower overall hghts. For
now NBM temperatures show a cooling trend after Tuesday which is
likely due to an increase in moisture as southeasterly flow aloft
returns to the lower deserts.

PWATs are expected to increase back to around 1.5-1.8" by the middle
of next week which will bring rain chances back into the picture by
the Wednesday-Thursday timeframe when PoPs increase to around 20-40%
areawide. The GFS is even showing an easterly wave/inverted trough
arriving into southern AZ along with additional tropical Pacific
moisture on Wednesday which could boost rain chances significantly,
but we will likely have to wait for more run to run consistency as
these features are always difficult to resolve at longer time
scales. Either way, most of the GEFS and EPS members are showing
measurable precipitation across portions of the area by the middle
of next week.

&&

.AVIATION...Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Other than a remote chance for an isold SHRA/TSRA early this
evening, winds will be the only weather issue through Saturday
evening under frequent mid/high cigs. Minimal 10% chances of a
SHRA/TSRA impacting a Phoenix terminal exists through mid evening
before abating by midnight with good confidence of winds finally
settling on a W/SW direction. Confidence is also good that the
typical nocturnal switch to east will occur later than usual well
after midnight. Any afternoon gustiness should be limited.


Southeast California/Southwest Arizona including KIPL and KBLH:
Gusty late afternoon/early evening winds will be the main weather
impact through Saturday evening under thickening mid/high clouds.
W/SW gusts 20-25kt will be common at both locations before speeds
relax overnight, and even becoming light and variable into the
morning. Virga/isold SHRA will be common Saturday afternoon, though
should yield minimal operational impacts.

&&

.FIRE WEATHER...
Residual moisture may spark a few showers and storms this afternoon
across south-central AZ. Rain chances will expand westward through
this weekend, becoming focused over the western districts Saturday
and Sunday. However, the chances for wetting rains will remain very
low at less than 10%. Afternoon minimum humidities will range from 7-
15% across southeast CA and between 20-35% for the the AZ deserts
today and will likely increase above 20-25% areawide starting this
weekend. Overnight recoveries will range from poor across the
western deserts to good across the eastern districts tonight and
increase to good areawide this weekend. Winds will remain elevated
out of the south to southwest, with the strongest gusts in Southeast
CA and along the Lower Colorado River Valley peaking between 20-30
mph this afternoon/early evening. Lighter winds, generally around 15
mph or less will transpire this weekend.

&&

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

&&

$$

SHORT TERM...Lojero
LONG TERM...Salerno
AVIATION...Benedict
FIRE WEATHER...Salerno/Lojero