886
FXUS65 KPSR 051027
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
327 AM MST Sat Sep 5 2026

.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 remains largely unchanged from 24 hours
ago. An elongated ridge of high pressure remains centered over the
Plains, stretching from the Mid-Atlantic back to the Rockies, with a
longwave trough stretching down the West Coast with the low pressure
centered over the Pacific Northwest. Additionally Hurricane Marie
continues to spin well off the coast of the southern Baja Peninsula.
PWATs are low across the CWA early this morning, ranging from 0.7-
1.3". Models continue to show a dramatic increase in PWATs across SE
CA and SW AZ later today, with PWATs increasing to to 1.6-1.8"
thanks to tropical moisture from Hurricane Marie. The better forcing
today will be over SE CA and SW AZ (thanks to the aforementioned
longwave trough). Due to the combination of better forcing and the
dramatic increase in PWATs, rain chances will be confined to this
region this weekend. However, PoPs remain only around 10-20%.
Models show little to no CAPE, so any rain that does form will
likely only be light showers or sprinkles. However, most of the
activity may only be virga as the low levels remain dry, with dew
points in the 40s and 50s. Moisture will increase even more on
Sunday. However, the better forcing and better rainfall potential
will shift northward towards the Mohave Desert, Las Vegas, and
Grand Canyon areas. Elsewhere across the CWA, dry conditions are
expected due to the lack of forcing and instability.

With the aforementioned trough to our west still through the
weekend temperatures will continue to be near to slightly below
normal. Afternoon highs today will be in the upper 90s to low 100s
across the lower deserts and in the 90s across the higher terrain
areas. Ample cloud cover across SE CA and SW AZ will likely lead
to many locations out there falling just shy of the triple digit
mark. Temperatures will warm a few degrees tomorrow as the trough
begins its migration northwestward. Morning lows both days will
range from the mid 70s to low 80s across the lower deserts and the
mid 60s to mid 70s across the higher terrain.


&&

.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 1025Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather concerns will exist through through the forecast
period under increasing mid/high level cloud decks. Confidence
remains moderate that an easterly shift will occur early this
morning (around 12Z at KPHX). Winds are then expected to gradually
transition to westerly by late this afternoon, however there could
be a few hours of a southerly cross-runway component before the
full westerly switch occurs. Westerly winds will then prevail
through the remainder of the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through the forecast period
under thickening mid/high level clouds. Winds will follow general
diurnal patterns, fluctuating between westerly to southeasterly
at KIPL and southerly to southwesterly at KBLH with extended
periods of calm and vrb. A period of light SHRA will be possible
at both terminals beginning this evening, but accumulations will
be minimal and no operational impacts are expected.

&&

.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
will be 15-30%, with good (40-60%) overnight recoveries, area
wide through the week. Winds will generally be light and follow
their typical diurnal tendencies, with some occasional afternoon
upslope breeziness.

&&

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

$$

SHORT TERM...Berislavich
LONG TERM...Berislavich
AVIATION...Salerno
FIRE WEATHER...Berislavich

NWS PSR Office Area Forecast Discussion