262
FXUS65 KPSR 050510
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1010 PM MST Fri Sep 4 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- A plume of moisture will shift into southeast California and
southwest Arizona this weekend yielding chances for light showers.

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

- Increased thunderstorm chances will return to the region during
the latter half of 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 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather concerns will exist through Saturday night under
frequent mid/high level cloud decks, but lack of thunderstorms.
Confidence is good that west winds will transition to easterly
overnight, but temporally later than usual. The transition back to
west Saturday afternoon should be more abrupt than Friday with
minimal gusts and the westerly component holding well into Sunday
morning.


Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Saturday night under
thickening mid/high level cigs. Confidence is good that winds will
vary between south and west with minimal gustiness, and periods of
nearly calm conditions during the morning. Widespread virga with
very isold -SHRA will be common Saturday afternoon, though should
yield little to no 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...18
FIRE WEATHER...Salerno/Lojero

NWS Phoenix (PSR) Office