395
FXUS65 KPSR 052300
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
400 PM MST Sat Sep 5 2026

.UPDATE...
Updated Aviation

&&

.KEY MESSAGES...

- A plume of moisture will yield minimal rain chances across
portions of southeast California and southwest Arizona through the
weekend.

- Mostly dry and quiet weather conditions can be expected early next
week before thunderstorm chances increase by the latter half of the
week.

- 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/...
Latest objective analysis reveals the subtropical ridge situated
over the southern Plains while a broad upper trough encompasses much
of the west coast with low pressure pressure centered across the
Pacific Northwest. This overall pattern configuration is continuing
to result in southwesterly flow aloft, which has helped advect a
plume of mainly mid to upper-level moisture originating from
Hurricane Marie, spinning well of the coast of the Baja Peninsula,
into the region. The highest moisture content is expected to be
confined across southwest AZ and southeast CA where PWATs are
expected to climb in excess of 1.5" later today. This increase in
moisture combined with some upper-level forcing from the
aforementioned trough will cause isolated to scattered light showers
to break out. However, since much of the moisture is mostly in the
mid to upper-levels with the low-levels rather dry as surface
dewpoints are in the 40s and 50s, any rain that falls will be mostly
virga/sprinkles with little to no measurable accumulations. Some
better low-level moisture will be in place on Sunday, however, most
of the upper-level forcing will be shifting northward with the
Mohave Desert Region expected to have the better rainfall potential
as guidance shows an extensive area of light to locally moderate
intensity rainfall materializing. Across south-central AZ, generally
dry and quiet weather conditions are expected through the rest of
the weekend as the combination of the lack of instability and
forcing for ascent will hinder storm activity. With the rainfall
activity over the Mohave Desert Region on Sunday, outflow winds from
the northwest are expected to impact much of the lower deserts with
afternoon/early evening peak gusts of 20-30 mph likely.

Temperatures today and Sunday will continue to run near to a few
degrees below normal, with today being the cooler day given the
presence of more abundant mid to high clouds. The cooler
temperatures for this afternoon are expected across the western
deserts where the thicker cloud cover will likely cause readings to
fall shy of the triple digits, whereas further east into south-
central AZ, slightly warmer readings into the low 100s under more
sunshine can be expected. Temperatures will warm a few more degrees
on Sunday under slightly less cloud cover.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Ensemble model guidance has come into better agreement on the
synoptic pattern for the beginning of the workweek. Ensemble members
show the longwave trough over Western CONUS lifting northeastward
and pushing into the Northern Rockies, TC Marie moving
north/northwestward (staying well off the coast of California), and
the subtropical ridge pushing back into the Desert Southwest. With
the subtropical ridge building back overhead, H5 heights will rise
to around 591-594 dm. This increase in heights aloft will result in
a gradual warming trend. The NBM shows afternoon high temperatures
increasing to 100-108 degrees across the lower deserts and 90-100
degrees across the higher terrain. Temperatures of this magnitude
are slightly above normal, which will result in widespread Moderate
HeatRisk across the lower deserts. The aforementioned synoptic
pattern will also result in the continuation of dry southwesterly
flow aloft. PWATs are expected to drop to around 1.3-1.6", resulting
in mostly dry conditions across the CWA.

Heading into the later half of the workweek, ensemble model guidance
continue to disagree on the synoptic pattern. Not only do the models
differ on the strength and positioning of the subtropical ridge,
they also differ on the strength and positioning of the low pressure
system over the eastern Pacific. Overall the EPS has a stronger
solution, it is showing a stronger subtropical ridge along with a
stronger/deeper low pressure system in the Pacific (in fact it is
showing a closed low). Additionally, the EPS has both of these
features further west. The EPS shows the high maxing out around 597
dm during the middle of the week, with the center stretched across
the Plains, and then the high weakening slightly, but moving
overhead by the end of the workweek. Then the GEFS is showing a
weaker ridge and a weaker, open wave trough, with both of these
features further east. These difference can be seen in the large
temperature spreads in the NBM interquartile range (with the EPS
being a warmer solution and the GEFS being a cooler solution). The
NBM continues to lean more towards the GEFS, with a gradual cooling
trend beginning Wednesday. Both ensemble models do show a return of
moisture by the middle of next week, with PWATs increasing to around
1.5-1.8" (EPS has slightly higher PWATs). This increase in moisture
will result in rain chances returning to the region as early as
Wednesday. The NBM shows PoPs of 20-40% area wide by the Wednesday-
Thursday timeframe. The GFS also shows an inverted trough moving
through the region during the middle of next week. If this were to
occur it would significantly increase rain chances for the region.
Despite this, both the GEFS and EPS do show measurable rainfall
returning to at least some portions of the region during the latter
half of the upcoming workweek. However, forecast confidence remains
low and we`ll have to wait to see how the models evolve over the
coming days.

&&

.AVIATION...Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Uncertainty in wind directions will be the only weather issue
through Sunday evening under periods of thicker mid/high cloud decks
and spotty virga. A westerly wind component will hold well into the
overnight, and may never complete an easterly switch at KPHX. A
revision back to a pronounced west direction should occur by late
morning with some modest gusts Sunday afternoon.


Southeast California/Southwest Arizona including KIPL and KBLH:
Thick mid/high cigs with virga/sprinkles will persist through Sunday
evening with little to no operational impacts. Confidence is good
that a southerly wind component will generally become NW by late
Sunday morning with gusts 20-25kt developing mid/late afternoon.

&&

.FIRE WEATHER...
Near to slightly below normal temperatures continue through the
weekend. A gradual warming trend begins early next week before
another cooling trend is expected for the end of the workweek.
Rain chances today will be confined to the western districts, but
chances for wetting rainfall remain very low. Afternoon minRH`s
today will be 15-30%, increasing slightly starting on Sunday with
values above 20% area wide through much of next week along with good
overnight recoveries. Winds will generally remain light today before
some elevated afternoon/early evening breeziness out of the
northwest return on Sunday 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 next week.

&&

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

&&

$$

SHORT TERM...Lojero
LONG TERM...Berislavich
AVIATION...18
FIRE WEATHER...Lojero/Berislavich