735
FXUS65 KPSR 021737
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1037 AM MST Tue Sep 2 2025

.UPDATE...Updated 18z Aviation Discussion.

&&

.KEY MESSAGES...

- Temperatures will gradually cool over the course over the next
  several days, with widespread below-normal readings expected by
  the end of the week

- Increasing moisture will promote daily shower and thunderstorm
  chances for parts of the region into the weekend

- Gusty winds, localized blowing dust, and isolated instances of
  heavy rainfall will be common with any thunderstorms throughout
  the week

&&

.SHORT TERM /Today through Wednesday/...
Current objective analysis reveals our seasonal sub-tropical high
centered over southern Utah at this time, inducing south to
southeasterly flow over the Desert Southwest. Thanks to this shift
in synoptic flow helping to bring increased moisture flux to parts
of the region, regional mesoanalysis now projects PWATs along the
Lower Colorado River Valley near 1.5-1.7". BUFR sounding for Yuma
for this morning show much this moisture spread throughout the
column, with a decent saturated layer in the mid-levels of the
atmosphere. This moisture profile, combined with a local area of
vorticity near the Arizona-Mexico border, and favorable jet
dynamics, promoting large-scale ascent, will likely spark some
early morning showers, and perhaps some embedded thunderstorms
over parts of Southwest AZ and Southeast CA. Main impacts with
this activity will be some heavy downpours, occasional lightning,
and some isolated gusty winds.

Forecast uncertainty increases for this afternoon as lingering
cloud clover from morning activity may inhibit further convective
potential across Southeast California. However, some pop-up
shower or storms cannot be completely ruled over this area, but
most afternoon convection should be focused further to the east.
In fact, there is decent agreement amongst hi-res guidance that
storms will initiate near the international border in central and
central Pima County, where afternoon MLCAPE values near 1000 J/kg
could be tapped by another vorticity center emanating from an
inverted trough. Storms that do form may push out gusty winds
exceeding 35 mph, generating areas of dense blowing dust.
Localized flash flooding will also be a concern under the heaviest
cells.

With decent moisture profiles in place, rainfall chances will
persist into Wednesday, but confidence regarding potential activity
is low at this time. Similar thermodynamic profiles to Tuesday
will remain in place over a broader area, and cloud cover looks to
be less, promoting better destabilization over SE California and
SW Arizona. However, hi-res models do not appear too excited for
activity at this time. If enough destabilization were to occur,
showers and storms around prominent terrain features would likely
occur at a minimum. The one thing that might be lacking is broader
ascent in the mid and upper-levels, limiting convection closer to
the desert floor. Outflow boundaries from high terrain activity
would be the triggering mechanism needed to spark lower-evevation
storms. Future model runs will yield trends allowing for greater
confidence regarding further rainfall activity and coverage.

&&

.LONG TERM /Thursday Through Monday/...
Southeasterly flow will remain in place as we head into the latter
portion of the week, keeping rain chances in the forecast at least
through Saturday for parts of the region, especially for those
typical high terrain areas. For the Phoenix metro, the Thursday-
Friday timeframe looks to be the best for rainfall as a reinforcing
push of moisture enters the region, making conditions more conducive
for widespread lower-desert activity. However, there are some
factors that are making it difficult to pinpoint the exact day of
activity. Thursday activity maybe limited across parts of the
state due to cloud cover being sheared off from what could soon
become Tropical Storm Lorena. Friday may be the better day for
activity due to slightly better moisture availability and less
cloud cover, a setup more conducive for widespread convective
activity. One thing that appears more certain though is decreasing
temperatures through the workweek. Weakening high pressure, along
with increased moisture and cloud cover, will help bring
temperatures to below normal levels by the latter half of the
week, with some lower desert locations even struggling to reach
the triple digits by as early as Wednesday.

By the end of the weekend and into the start of next week, signs
point to dry southwesterly flow making its return across the region,
likely shutting down rain chances for a while. Drier conditions are
likely to result in a rebound in regional temperatures, with most
areas outside of lower elevation communities seeing the return of
triple digits by early next week.

&&

.AVIATION...Updated at 1735Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty winds and potential for reduced visibilities will be the
main aviation concern this TAF period. Theses gusty winds will
generally be between 20-25 kts and will continue through the
afternoon, but look to subside by this evening. Convective
activity will mainly be focused to the south and west of the
terminals this afternoon and currently do not look to propagate
into the Phoenix Metro area, but could produce outflows from the
SW that could result in a few hours of blowing dust. Winds will
have a late switch out of the west by 00-01Z before weakening for
the overnight period, where VRB conditions will be common. SCT-BKN
mid to high lvl clouds will prevail over the region with bases
aoa 10 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
The main aviation concerns this TAF period will be the potential
for VCSH/VCTS and gusty winds at both terminals. A line of storms
have developed generally west of the terminals, but redeveloping
showers and storms are anticipated over the next several hours,
primarily at KIPL but KBLH could be affected as well at this time.
KIPL will keep a NNW`rly component through the afternoon, followed
by VRB conditions for the overnight period. Another round of
showers and storms will be possible at KBLH late this afternoon
with winds predominately out of the W-NW. Cloud bases are expected
to be aoa 10 kft, however could briefly lower to around 7-9 kft
with any passing shower/storm.

&&

.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 the middle of the
week, likely rising even higher later this week due an additional
moisture push and cooling temps. MaxRHs will follow a similar
trend, with good to excellent overnight recoveries expected into
the weekend. Near to slightly above normal temperatures will be
common across the region today before widespread below normal
readings are observed through the latter part of the week and into
the weekend.

&&

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

$$

SHORT TERM...RW
LONG TERM...RW
AVIATION...Ryan
FIRE WEATHER...RW