878
FXUS65 KPSR 061957
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1257 PM MST Sun Sep 6 2026

.KEY MESSAGES...

- Aside from some light shower activity lingering across Joshua
  Tree National Park through this afternoon, mostly dry and quiet
  weather conditions are expected through the first half of this
  week.

- Thunderstorm chances will start to increase, mainly across
  central and eastern Arizona, by the latter half of the upcoming
  week.

- As high pressure builds over the region, temperatures will heat
  up to above normal levels through the middle of the week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
Latest water vapor satellite imagery as well as streamline
analysis reveal the subtropical high pressure centered over the
southern Plains while an upper- level trough continues to be
situated across the Pacific Northwest. This upper-level trough
will finally begin to migrate east northeastward later today
through Monday towards the Intermountain West and into south-
central Canada by Tuesday while weakening in the process. As it
does so, it will allow the subtropical ridge to gradually build
westward into our neck of the woods during the first half of the
upcoming week.

A plume of tropical moisture originating from Hurricane Marie,
which continues to spin well west of the Baja Peninsula Coast, and
an upper-level jet streak over the Great Basin Region are
supporting an extensive band of light to locally moderate
rainfall, which extends from the southern CA coast east-
northeastward towards the Mohave Desert Region. The bulk of the
activity is expected to remain over these areas through this
evening with Joshua Tree National Park expected to be the only
area within our CWA to observe some light rainfall activity. With
this large cluster of rainfall, outflow winds from the northwest
are expected to impact much of the lower deserts during the
afternoon and evening hours, with peak gusts of 20-30 mph likely
as depicted by the hi-res guidance. Afternoon high temperatures
will top out between 102-106 degrees across the south-central AZ
lower deserts with slightly cooler readings between 98-105 degrees
across the western deserts due to more cloud cover.

Conditions will remain quiet during the first half of the week as
the overall lack of instability and forcing will hinder storm
activity. The bigger story with the building ridge of high
pressure will be the rising temperatures. Latest guidance show 500
mb heights rising from 590-593dm on Monday to 594-597dm by early
Wednesday, which is near record strength for this time of the
year. As a result, temperatures will gradually heat up with the
latest NBM now showing lower desert highs reaching the upper 100s
to some areas approaching 110 degrees by Tuesday and likely be
near similar values through the middle portion of the week. These
high temperatures combined with early morning lows in the mid to
upper 80s are likely to cause HeatRisk levels to reach the Major
Category and thus if these temperature trends continue, extreme
heat products will likely be needed for much of the lower deserts
in the subsequent forecast packages.

&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Heading into the latter half of the workweek, ensemble model
guidance has come into slightly better agreement on the overall
synoptic pattern. The models have come into better agreement on
the placement of the features, but still differ on the overall
strength of the features. Both the GEFS and the EPS show a
shortwave trough across the northern CONUS and southern Canada, a
broad subtropical ridge stretching across much of the lower 2/3 of
CONUS, along with a closed low off the coast of northern
California. The EPS continues to be the slightly stronger
solution, with a stronger closed low in the Pacific and a slightly
stronger subtropical high. This overall better agreement is
reflected with the slightly smaller temperature spread in the NBM
interquartile range, which has narrowed to less than 5 degrees.
The GEFS show the high at peak strength (H5 heights of 594-597 dm)
on Wednesday before weakening (H5 heights of 591-594 dm) by the
latter half of the week. The high looks to continue to weaken (H5
heights of 588-592 dm) heading into the weekend. Therefore,
temperatures are forecasted to remain about 5 degrees above normal
during the middle of the week before beginning a slight cooling
trend for the end of the workweek and into the weekend closer to
near normal levels.

As for shower and storm chances, the ensemble members continue to
show those chances starting to increase, for at least portions of
the CWA, beginning on Wednesday. PWATs look to increase to around
1.5-1.9" for the latter half of the week, so moisture should not be
a limiting factor. With the high forecasted to move overhead,
rain chances will likely be limited to the higher terrain areas
across eastern Arizona on Wednesday and Thursday. Rain chances
may extend into the lower deserts of south-central Arizona heading
into the weekend. However, the current WPC PoPs of 30-40%, for
Friday into Saturday, seem rather aggressive, especially this far
out. WPC`s Saturday PoPs of 10-30% seem more reasonable.

&&

.AVIATION...Updated at 1741Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main weather concern will be gusty winds later this evening.
Winds will maintain a westerly component throughout the period
with winds shifting out of the NW by 23Z-00Z where gusts will
also begin to ramp up. KPHX and KDVT can expect gusts between
20-25kts between 23Z-04Z, while elsewhere may also experience
brief periods of gusty conditions but not enough to warrant
inclusion in the TAF. Tomorrow morning is expected to have some
VRB conditions but should still maintain a mostly westerly
component.

Southeast California/Southwest Arizona including KIPL and KBLH:
Thick mid/high cigs with at most virga/sprinkles will persist
through this evening, albeit with little to no operational impact.
Confidence remains high that NW winds with gusts between 20-25kts
will develop mid/late this afternoon.

&&

.FIRE WEATHER...
Temperatures will be slightly below normal across SE CA today.
Otherwise, temperatures will warm to above normal levels through
the middle of the week. Rain chances today will be confined to
Joshua Tree National Park, with chances for wetting rainfall very
low. MinRH`s will generally be around 20-30% area wide through
much of this upcoming week with good overnight recoveries. Some
elevated afternoon/early evening breeziness out of the northwest
can be expected this afternoon and evening with peak gusts of
20-30 mph. A more typical diurnal wind pattern with some
occasional afternoon upslope breeziness can be expected through
much of this coming week.

&&

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

&&

$$

SHORT TERM...Lojero
LONG TERM...Berislavich/Lojero
AVIATION...Ryan
FIRE WEATHER...Lojero/Berislavich