852
FXUS65 KPSR 131928
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1228 PM MST Sun Sep 13 2026

.KEY MESSAGES...

- Abundant moisture will remain situated across the eastern half
  of Arizona providing enhanced chances for showers and
  thunderstorms through the middle portion of the week, especially
  over the mountain locations.

- Although uncertainty remains, there will be potential for some
  storms to produce strong gusty and heavy rainfall leading to
  localized flash flooding over the next several days.

- Near to slightly above normal temperatures are expected
  throughout the upcoming week.

&&

.SHORT TERM /Today through Monday/...
Latest objective analysis depicts the subtropical ridge of high
pressure situated over Texas while a robust upper-trough is
situated over the northwestern CONUS. The ridge of high pressure
is forecast to reposition over the southeastern states while broad
troughing will remain situated to the northwest of the region
through much of the upcoming week. This overall pattern
configuration will continue to result in south to south-southwest
flow over the area, aiding with periodic moisture influxes and
thus an elevated potential of shower and thunderstorm activity,
mainly across central and eastern AZ.

The 12z KPHX sounding from early this morning depicted a very moist
airmass in place with a low-level mixing ratio of 14 g/kg and PWATs
in excess of 1.9". The abundant moisture already in place combined
with strong daytime heating will result in MLCAPE values this
afternoon between 1500-2000 J/KG across much of south-central AZ
with near zero convective inhibition. Even though the thermodynamics
look very favorable for thunderstorms, the main limiting factor
for widespread coverage continues to be lack of good upper-level
forcing for ascent given that most of the jet dynamics associated
with the troughing pattern over the northwestern states will
remain to the north of the region. Therefore, thunderstorm
activity this afternoon through early this evening will be
orographically induced, with the latest hi-res guidance showing
isolated to widely scattered activity across the eastern and
southeast third of AZ this afternoon. However, even though the hi-
res guidance shows little to no activity further west into Pinal
and Maricopa Counties, given the lack of convective inhibition in
place, it will not take much to get storms to pop up in the
smaller terrain features such as the Table Top Mountains and the
Estrellas, with potential outflows potentially instigating new
storm development in the lower elevations, including into portions
of the Phoenix area. With these storms that do develop, given the
very moist environment in place, heavy rainfall leading to
localized flash flooding will be the primary threat with a
secondary threat being strong downburst wind gusts given that
DCAPE values are expected to range between 1000-1200 J/KG. With
the loss of daytime heating, storm activity should diminish by
early this evening.

Heading into the overnight and early morning hours on Monday,
several of the hi-res guidance indicate a round of elevated
showers and storms materializing across portions of south-central
AZ, including the Phoenix area. This is likely due to a northern
Sonora storm complex that is being depicted by guidance to develop
later this evening and is likely to send a gravity wave/outflow
northward and aid as the triggering mechanism for convective
development. Latest NBM is honing in on this potential, showing
PoPs between 30-50% from central Phoenix eastward into Gila
County. Heading into Monday afternoon, there is a greater signal
for better storm coverage across southeast AZ with activity
impacting the higher terrain areas east of Phoenix. However, given
that the convective inhibition will once again be nearly absent
due to abundant moisture in place with low-level mixing ratios of
12-14 g/kg and at least 1500 J/KG of MLCAPE assuming the morning
activity does not disrupt the daytime heating significantly, a
modest outflow is likely to be sufficient to trigger additional
storm activity across the lower deserts of south-central AZ.
Similar to today, heavy rainfall leading to localized flash
flooding will be the primary threat.

Temperatures during the next couple of days will be near to slightly
above normal levels with afternoon highs ranging between 100-107
degrees, with the warmest readings across the western deserts,
along with above normal early morning lows in the low to mid 80s.
This will maintain the overall HeatRisk level in the moderate
category.

&&

.LONG TERM /Tuesday through Saturday/...
The weather pattern through at least the middle of the week will
continue to support good moisture levels over at least the eastern
half of Arizona and likely improved upper level ascent for Tuesday-
Thursday. Tuesday may involve a brief period of drier air moving
into south-central Arizona from the southwest and this shows up in
the fairly limited PoPs Tuesday afternoon/evening. However, NBM
guidance shows a resurgence of moisture and rain chances during the
overnight hours Tuesday night/Wednesday morning. Chances Wednesday
into Thursday are also looking better with a potential disturbance
tracking northward into central/eastern Arizona at some point.
Needless to say, the model differences call into question the best
timing for rain chances and the exact areas, but as long as the
upper level support and good moisture remain present chances will
remain elevated.

WPC has added a slight risk on the Days 2-4 (Monday- Wednesday)
Excessive Rainfall Outlooks over the eastern Arizona high terrain.
It would not be surprising for subsequent issuance`s of the EROs to
extend the risk through Thursday or even Friday depending on the
forecast available moisture. Although the risk for heavy rainfall
and flooding will be present through at least the middle of the
week, the risk for strong downdraft/outflow winds is likely to
decrease with guidance showing decreasing forecast DCAPEs. Models
are still trending toward drier air finally moving eastward through
most of Arizona by Friday or Saturday. This should mostly shut down
rain chances over the lower deserts and decrease chances over higher
terrain areas.

Temperatures throughout the entire week are expected to remain
fairly close to seasonal normals with the lowest forecast highs
occurring on Tuesday and Wednesday. As long as models are correct
with the drying trend late in the week into next weekend,
temperatures are favored to drift back to above normal with highs
more in a 103-108 degree range by Friday or Saturday.

&&

.AVIATION...Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Very low confidence forecast through Monday given vast uncertainty
in thunderstorm development/coverage and resulting effects on winds
and flight categories. Confidence is good that an extended period of
southerly cross runway winds will exist early this afternoon before
becoming W/SW by late afternoon. Similar to yesterday, TSRA may
develop over terrain features with modest outflow winds and isold
BLDU around the airspace, but not directly impacting terminals
(chances less than 25%). However, its not out of the question for
westerly winds to be disrupted at some point this evening by effect
from storms.

Models still want to blossom SHRA/TSRA over/near the Phoenix metro
Monday morning around sunrise, though confidence in location and
coverage is low, and only justifying a Prob30 mention at this time.
If SHRA/TSRA indeed materialize, erratic wind directions and
potentially briefly lower flight categories will be possible through
mid/late morning. Trends in winds and additional convective
development the remainder of Monday will be highly contingent on
morning activity (or lack there of).

Southeast California/Southwest Arizona including KIPL and KBLH:
No weather concerns will exist through Monday afternoon under mostly
clear skies. Confidence is very good that winds will behave similar
to the past 24 hours varying between a SE and SW heading. Afternoon
gusts around 20kt will be common at KBLH.

&&

.FIRE WEATHER...
Chances for scattered showers and isolated storms will continue
today before increasing and becoming more widespread into the south-
central Arizona lower deserts beginning Monday. Moisture levels will
remain high enough to support localized heavy rainfall with any
storms. Minimum humidity levels over the next several days will only
fall into a 15-25% range in western districts and 25-40% in eastern
districts. This will follow fair to good overnight recovery of 40-
70%. Outside of thunderstorms, winds will generally remain light
with a south to southwest heading though nearly calm conditions
will be common in the morning hours.

&&

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

&&

$$

SHORT TERM...Lojero
LONG TERM...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman