654
FXUS65 KPSR 010921
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
221 AM MST Mon Sep 1 2025

.KEY MESSAGES...

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

- Increasing moisture will help to gradually enhance rain chances
  across the region over the next several days, with the best
  chances today focused over the Arizona high terrain

- Weakening high pressure, along with increasing moisture, will
  promote gradually cooling temperatures during the upcoming
  workweek

&&

.SHORT TERM /Today through Tuesday/...
Morning 500mb analysis reveals high pressure continuing to sit over
the Desert Southwest and Great Basin, while WV imagery indicates
enhanced moisture remaining generally over Southeast Arizona,
promoting mostly dry and warmer-than-normal conditions across our
forecast area. For Labor Day, there will not be much change
across the region compared to the rest of the weekend so far, as
temperatures for lower desert areas are once again expected to
range between 104-110 degrees while the vast majority of locations
remain dry. The once exception to this will be the typically
wetter spots of Gila County where a 30-40% chances of afternoon
showers and thunderstorms exist.

The expectation is that with unimpressive moisture profiles, most
lower desert areas should remain dry, but some very isolated
convection cannot be completely ruled out around the Phoenix metro
this evening. The spark for any possible storms would likely be an
outflow boundary from distant convection over higher terrain areas,
but most hi-res guidance has activity mostly fizzling out once is
moves off the mountains. The more favorable outcome for rain
around the metro would be if we can get multiple outflows that
collide, but models are not too enthusiastic about that solution.
Even if no rain occurs, there still could be some impacts
associated with potential outflows, such as: gusty winds in
excess of 35 mph, and some hazy conditions caused by lofted dust.

By early Tuesday morning, the focus for potential rainfall shifts to
Southwest Arizona and Southeast California as there are indications
of a Sonoran MCV developing concurrently with an increase in
moisture flux across these areas. Depending on how much rainfall
were to occur, and how long the associated cloud cover may
linger, it is not out of the question that more pop-up shower and
storms, mostly around prominent terrain features, are observed
around these same areas Tuesday afternoon thanks to the decent
moisture profiles that will be in place. However, this second
round of rainfall is going to be heavily dependent on if there
enough insolation that occurs to destabilize the atmosphere
to a point when convection can initiate.

&&

.LONG TERM /Wednesday Through Sunday/...
With more favorable S/SE flow in place, moisture advection will be
sustained and allow for daily chances for showers and thunderstorms
remainder of the week and into the weekend for parts of the region.
Most of the activity at first will be focused around enhanced
terrain features such as the Kofa and Chocolate Mountains, areas
around Joshua Tree NP, and the typical spots in southern Gila
County. Areas along the desert floor will also have chances during
the middle to latter portions of the week to see rainfall
activity, but that will be determined by any triggering mechanisms
(such as outflow boundaries) that move off those high terrain
areas.

For the Phoenix metro, outside of any isolated activity that pops
due to any aforementioned outflow boundaries during the first
part of the week, the best timeframe to rainfall looks to be the
Thursday-Saturday window. Models points toward a secondary surge
of moisture that will push PWATs closer to 150% of normal, which
should be enough to help initiate some more widespread showers
and storms across South-Central Arizona. Now, can rain be expected
all three of these day? That seems unlikely as what occurs on one
day will influence what occurs on the next, so pinpointing the
exact timing of rainfall for the metro is still a bit uncertain at
this time. Looks like by Sunday, flow aloft will switch back to
the southwest, drying the region out and suppressing rain chances
for next week.

In terms of temperatures, high pressure overhead is expected to
weaken slightly, thanks to a disturbance off the Pacific Coast,
indicating the presence of a cooler atmospheric profile. This,
combined with increasing moisture, along with rainfall activity
and associated cloud cover, will send temperatures on a downward
trajectory over the next several days, with some lower desert
areas potentially struggling to reach into the triple digits by as
early as Thursday. I`m sure that this will be welcome news for
many after the what was experienced around this time last year.

&&

.AVIATION...Updated at 0559Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Easterly winds will prevail through midday Monday, with current
gusty winds expected to subside over the next few hours. Typical
afternoon west shift is not anticipated Monday. Instead a period
of light variability or light southerly component does look to
develop around mid to late afternoon. Good confidence for outflow
wind impacts Monday evening, with winds most likely from the east
to northeast. Timing as early as 00Z is possible, but 01-03Z is
most favorable at this time. Latest odds of outflow gusts >30kt
are around 40-50%. Confidence is too low for VCSH/VCTS mention in
the TAFs, as activity looks to dissipate as they drop toward the
Phoenix area. VFR conditions with cloud bases staying mostly at
above 10K ft AGL will prevail.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather concerns are expected through the next 24
hours under mostly clear skies. Winds will favor the W/SW at KIPL
through this evening before turning SE Monday morning. At KBLH,
winds will favor the SSW-SSE. Expect wind speeds to remain mostly
aob 7 kts, with periods of calm or VRB conditions at both
terminals.

&&

.FIRE WEATHER...
Increasing moisture levels across the Desert Southwest will result
in a gradual enhancement of daily shower and thunderstorm chances
over the next several days. Due to this increased moisture flux,
MinRH values will remain around 15-25% through most of the week,
potentially rising even higher later in the week due an additional
moisture push and cooling temps. MaxRHs will follow a similar
trend, with modest overnight recoveries Monday into Tuesday
becoming good, to even excellent, by late week. Above-normal
temperatures will last one more day before temperatures gradually
cool toward below seasonal levels by mid to late week.


&&

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

$$

SHORT TERM...RW
LONG TERM...RW
AVIATION...Benedict/Smith
FIRE WEATHER...RW