733
FXUS65 KPSR 311129
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
429 AM MST Sun Aug 31 2025

.UPDATE...Updated 12z Aviation Discussion...

&&

.KEY MESSAGES...

- Warmer-than-normal temperatures will persist through the
  remainder of the Labor Day Weekend

- Generally dry conditions are expected to prevail over most of
  the region into the start of next week, with a slight chance of
  a shower or storm over the Arizona high terrain

- Chances for rainfall increase across the lower deserts by the
  beginning of the workweek as better moisture begins to envelope
  the Desert Southwest

&&

.SHORT TERM /Today Through Monday/...
Early morning analysis reveals strong upper-level ridging
encompassing much of the western CONUS, while a couple of weak
disturbances spinning off the West Coast. With high pressure
overhead, and drier-than-usual air for this time of year in place,
the remainder of the Labor Weekend looks to be dry and relatively
warm for this time of year. This setup will promote a continued
increase in day-to-day high temperatures across the region, with
highs this afternoon running a good five degrees or so above
normal for the end of August, which translates to lower desert
readings this afternoon ranging between 105 to around 110 degrees
in the hottest spots. A very isolated shower or thunderstorm
cannot be completely ruled out over the high terrain in Gila
County, but the vast majority of rainfall activity across the
region will be confined to Southeast Arizona and areas around the
White Mountains.

Heading into Monday, and the start of September, conditions are
unlikely to change much as high pressure remains overhead, allowing
for and warmer-than-usual start to the month. However, one change
that will help setup conditions for the remainder of the week will
be a slight shift in the center of circulation of the ridge, switch
flow aloft from southwesterly to more of a east/southeast component.
This will help bring increasing moisture to the region. However,
expectations for any quick ramp-up of monsoonal activity should be
tempered as rain chances will primarily increase only for higher
terrain areas east of the Phoenix metro. Does this completely
exclude lower desert areas from seeing rainfall late Monday? No, as
hi-res guidance does hint at the potential for some activity to move
off the high terrain and down toward the Phoenix metro. Any lower
desert activity would likely be short lived and very hit or miss.
The more likely impact over the Phoenix area would be strong outflow
winds from distant higher terrain showers and storms. In fact, there
is already a decent signal from the HREF of one of these features
extending down to the lower deserts, highlighting most of Pinal and
the eastern half of Maricopa Counties in a ~50% chance of seeing
wind gusts reaching or exceeding 35 mph. Outside of any active
conditions they may come to fruition, temperatures Monday will be
slightly cooler compared to today, likely a response to
increasing moisture, but will continue to run above-normal.

&&

.LONG TERM /Tuesday Through Saturday/...

Ensemble forecasts agree that moisture will continue to be on the
uptrend across the Desert Southwest heading into the middle of next
week, allowing for increasing shower and thunderstorm chances for
the region. Parts of the lower deserts may get in on the action
as early as Tuesday morning as there are signs that isolated
elevated convection, likely set-off by a mid-level wave or perhaps
a Sonoran MCV, will be seen over portions of Southwest Arizona
and Southeast California. Better moisture availability will
actually be over these areas mentioned above compared to the
remainder of our forecast area, so it is not out of the question
that areas around Joshua Tree NP, along with areas around the
Chocolate and Kofa Mountains, see daily isolated activity through
much of the week. The mountains of Gila County are also included
in on these daily shower and thunderstorm chances through the end
of the week.

Else where across the lower deserts of South-Central Arizona,
specifically the Phoenix metro, the best chances for rainfall
appear to be latter in the workweek, more toward the Thursday-
Friday timeframe as a reinforcing push of moisture pushes PWATs
closer to 1.5-1.8" or 150% of normal for the beginning of
September. Similar to Monday evening, storms outside of this
timeframe cannot be completely ruled out, but any convective
activity will be heavily reliant on outflow boundaries from
distant thunderstorm activity.

In terms of temperatures, there appears to be some good news for
fans of of more seasonal temperatures. The sub-tropical ridge is
projected to weaken slightly thanks to a disturbance expected to
develop off the Pacific Coast. This, combined with increasing
moisture levels, and the potential for greater rainfall coverage
and cloud cover, temperatures will gradually fall through the week
and into the weekend, with the potential for many areas not
reaching into the triple digits by as early as Friday.

&&

.AVIATION...Updated at 0535Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the forecast period.
Light easterly or variable winds this morning will shift back out
of the WSW late this morning. Speeds should remain aob 7 kts at
all terminals. Skies will be mostly clear aside from a few passing
high clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected through the forecast period
under mostly clear skies. Winds will be primarily W to NW at KIPL
and W to SW at KBLH through today. Wind speeds should remain aob
6 kts, with periods of calm and vrb possible at both terminals.

&&

.FIRE WEATHER...
Generally dry conditions will persist through the remainder of the
long weekend, with the best chances of wetting rains coming Monday
over the parts of Gila County. Moisture levels will be on the rise
over the next few days, with MinRH values ranging between 10-15%
today, increasing to 20-30% by Tuesday. In turn, MaxRHs will
follow a similar trend with poor to modest overnight recoveries
expected tonight into Monday, becoming more decent by the middle
of the week. This increase in moisture will translate to a more
active period of monsoonal shower and thunderstorm activity.
Temperatures over the next week will peak today, with lower
desert highs nearing 110 degrees, before gradually falling through
the week toward below normal levels.

&&

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

$$

SHORT TERM...RW
LONG TERM...RW
AVIATION...Young/Salerno
FIRE WEATHER...RW