107
FXUS65 KPSR 161721
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1021 AM MST Tue Sep 16 2025

.UPDATE...Updated 18Z Aviation Discussion.

&&

.KEY MESSAGES...

- Above normal temperatures with localized Moderate Heat Risk will
  continue through Wednesday across the lower deserts with highs
  peaking at around 105 degrees today.

- Rain chances will increase over the next few days with the best
  chances focused across southeast California and southwest
  Arizona on Wednesday and Thursday and across south-central
  Arizona Thursday night into Friday.

- Temperatures are likely to return to normal later this week
  before slowly rising over the weekend into early next week.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
The weather pattern over the next several days is setting up to be
quite complicated with the dissipating TC Mario driving good
moisture northward into the Southwestern U.S. Currently, a weak
ridge still resides over the region stretching across Arizona into
portions of California, while a weak and dry upper level trough is
spinning off the coast of northern Baja. TC Mario is still slowly
moving to the north northwest roughly 350-400 miles west
southwest of the southern tip of Baja. The south southeasterly
flow in between TC Mario and the subtropical ridge to its east
continues to advect good moisture northward, now nearing the
southern border of Arizona. The latest analysis shows PWATs of
1.5-2.0" just south of our area. Some of this moisture is forecast
to advect into our area later today, first reaching Yuma and then
spreading through much of southeast California and southwest
Arizona. This should help to spark off some very isolated showers
and thunderstorms this afternoon across southeast California and
southwest Arizona focused mostly over higher terrain features.

Temperatures today will again be quite warm with H5 heights
sticking between 588-590dm. We are expecting highs across the
lower deserts between 102-105 degrees this afternoon, or up to 5
degrees above normal.

From later today into Wednesday, much better moisture will stream
into our area with PWATs increasing to between 1.4-1.8" by
Wednesday evening. The best moisture will again be focused
south and southwest of the Phoenix area with the Hi-res CAMs
fixating on the best rain chances across Pima, Yuma, and Imperial
Counties during the afternoon and evening hours. There is still a
good deal of uncertainty with how fast the moisture surges
northward on Wednesday. The latest HREF forecast MUCAPE of
500-750 J/kg for Wednesday over the aforementioned areas may
allow for a few strong storms, but the instability may be
underdone as the GFS is hinting at MUCAPEs of 1000-1500 J/kg over
a small area. We will have to keep a close eye on how this evolves
over the next 24-36 hours as the chance for stronger storms may
increase.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As we stated yesterday, model uncertainty was still quite high for
later this week, so it`s not surprising the forecast has shifted
back to better rain chances for Thursday and Friday. Guidance
remains confident in good low and mid level moisture seeping into
the entire area by Thursday as the remnants of Mario inch toward
or reach the southern California coast. The remnants of Mario are
also likely to get incorporated into a larger scale trough off the
coast with a jet streak strengthening across our region Thursday
into Friday. Guidance is now showing even better upper level
forcing for Thursday and Friday, as well as at least some modest
upslope forcing into central Arizona. However, one negative factor
is guidance shows a good amount of dry air aloft surging into our
region from the southwest later on Thursday into Friday. This
drier air aloft should inhibit heavy rainfall to a degree.

The latest forecast calls for scattered showers and isolated
thunderstorms likely focused across southeast California during
the first part of Thursday before spreading into southern and
central Arizona by Thursday evening through the overnight hours
Thursday. NBM PoPs of 40-60% are seen across much of the area
Thursday and Thursday night. Rain chances for Friday are a bit
more uncertain, but with the drier air likely moving in from the
southwest chances are likely to be focused more across the Arizona
higher terrain. Forecast QPF amounts for the entire event show the
highest amounts of 0.5-0.75" across the western half of Maricopa
County through northern Yuma and much of La Paz Counties. Higher
elevations across southeast California could also see upwards of
0.5-0.75". Guidance also shows roughly a 5-15% probability of
seeing an inch or more of rainfall from this event with the
highest chances focused across western Arizona.

Temperatures later this week are certain to drop with the increase
in moisture, clouds, and decent rain chances. The latest NBM
guidance shows highs more on the lower end of guidance with
readings mostly in the mid 90s for Thursday and Friday. As ridging
gradually builds back over our region into the weekend and
conditions gradually dry out temperatures are sure to rebound.
Forecast highs are seen creeping back to around 100 degrees by
Sunday and potentially even toward 105 degrees by the middle of
next week.

&&

.AVIATION...Updated at 1720Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will continue to favor typical diurnal patterns through the
TAF period, with a little more of a WNW component early this
afternoon. Sustained wind speeds will mostly stay below 10 kts. A
few occasional gusts into the mid-teens are possible this
afternoon. A late-arriving weak outflow boundary from the south to
southeast may initiate an earlier easterly shift tonight.
Otherwise, easterly winds should develop by around midnight. FEW
to SCT cumulus are expected through the day, with bases around 10K
ft AGL, and there will be an increase in high clouds this
evening/tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will continue to favor typical diurnal wind components, with
speeds generally aob 10 kt. There is a low chance (<10%) for a
storm to develop nearby KIPL to the south/southwest this
afternoon, and an even lower chance at KBLH. If a storm does
develop it could push an outflow boundary through the terminal.
FEW to SCT cumulus are expected through the day, with bases around
10K ft AGL, and there will be an increase in high clouds this
evening/tonight. VCSH may develop towards the very end of the
current TAF period, mainly near KIPL, but better chances for
VCSH/SHRA will be just beyond the current TAF period (tomorrow
afternoon and evening). Due to this no VCSH/SHRA has been
introduced into the TAFs at this time.

&&

.FIRE WEATHER...
Today will again bring above normal temperatures while moisture
continues to increase. Even better moisture and cooling
temperatures are then expected going into the latter part of the
week as rain chances increase across the entire area. The best
chances for rain are likely to fall on Thursday and Friday. MinRHs
today will still dip down to around 20% before steadily
increasing to around 40% late this week. Winds will remain light
over the next few days with directions mostly following diurnal
trends.

&&

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

$$

SHORT TERM...Kuhlman
LONG TERM...Kuhlman
AVIATION...Berislavich/Benedict
FIRE WEATHER...Kuhlman