194
FXUS65 KTWC 311629
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
929 AM MST Sun Aug 31 2025

.SYNOPSIS...Isolated to scattered thunderstorms are expected to
develop this afternoon and evening, especially east and south of
Tucson. Gusty thunderstorm winds may produce blowing dust at
times. Shower and thunderstorm chances continue through the coming
week with day to day variability. High temperatures will be near
normal through mid-week, then become below normal the second half
of the week.


&&

.UPDATE...Mid-level clouds are beginning to dissipate across the
area with some shower activity just south of the international
border in northern Sonora. High pressure will be centered just to
the north of the CWA putting most of the area under east to
northeast flow aloft. This will help increase moisture a little
and with CAPE values around 500-1000 J/kg will likely lead to
isolated to scattered showers and thunderstorms mainly south and
east of Tucson this afternoon and evening. Tucson will be on the
western periphery of storm chances thanks to its closer proximity
to the high with storm chances 40-50 percent in Santa Cruz,
Cochise, Graham, and Greenlee Counties and around 20 percent in
Tucson. The 31/12Z HREF has backed off some on wind probabilities
but is still highlighting the Gila River Valley and the I-10
corridor in Cochise County as the most likely places for strong
winds. This is thanks to the northeast mid-level flow which will
allow storms to come off of the rim. DCAPE values will be around
1500 J/kg. Late this afternoon into the early evening the HREF has
a 20-35 percent chance for winds 45 mph or greater within 25
miles of a point from Safford down to Wilcox and east to San
Simon. This could cause some blowing dust issues as outflows move
through. Localized heavy rain could also be a threat but will be
secondary to strong outflow winds. See the previous discussion for
longer term details.

&&

.PREV DISCUSSION... /issued 333 AM MST Sun Aug 31 2025/

The center of the mid-level high/ridge will drift north today,
turning mean winds over southeastern Arizona to the east to
northeast. Increasing precipitable water values and MUCAPE values
this afternoon should allow for thunderstorm development, mainly
east and south of Tucson. With MUCAPE values of 500-1000 J/kg and
DCAPE to around 1500 J/kg, instability will be sufficient for
strong outflow winds, especially as thunderstorms move off the
White Mountains into the Gila River Valley and through Cochise
county. The range of solutions from the 00Z convection allowing
model suite is somewhat inconsistent in coverage/timing of
thunderstorms, causing wind probabilities to back off slightly.
However an environment for strong downdrafts should be in
place, which should bring an isolated blowing dust threat. If
thunderstorms move through the Interstate 10 corridor of Cochise
county, a blowing dust headline may be needed. At this point
though confidence remains low enough to preclude a product for
this afternoon/evening. The main threat should be winds and
lightning, though with briefly heavy rain associated with any
thunderstorm an isolated flash flooding threat can`t be ruled out.
At least a couple models bring convection as far west as Sells,
with central- eastern Pima likely sitting on the western periphery
of the favorable moisture/instability field. Subsequently
forecast thunderstorm chances range from around 20 percent in the
Tucson metro to 50 percent in Douglas.

Easterly mid-level flow will continue on Monday, bringing richer
moisture content through western Pima. Thunderstorm chances become
widespread across southeastern Arizona, though not terribly high
in any one location. A wetter solution like the 00Z NAM brings an
easterly wave out of Sonora and kicks off a healthy coverage of
thunderstorms. On the opposite end the EC ensembles keep this wave
to the south and only produces very slight chances. Without a
triggering mechanism like this wave it may be difficult to see
more than isolated coverage of thunderstorms Monday, but how
today`s thunderstorms play out could change that.

Atmospheric moisture will likely remain highest west of Tucson
with some drying to the east through mid-week. This makes day to
day thunderstorm chances less certain, with around 15-30 percent
chances each day. Ensembles continue to signal the possibility of
better synoptic support for thunderstorms by around Thursday-
Friday, increasing forecast chances a bit. Additionally there
remains the likely formation of a tropical system south/west of
Baja later this week as indicated by the NHC, potentially
providing a moisture boost to southeastern Arizona. The chances of
an eastern trajectory to impact southeastern Arizona however
remains very uncertain as most ensemble members keep the track
well to the west. As for the temperature trend this week, the
increasing activity and moisture the second half of the week
should bring temperatures below normal with near to above normal
during the first half.

&&

.AVIATION...Valid through 01/12Z.

Isolated to scattered thunderstorms thunderstorms this afternoon,
mainly after 31/20Z and south and east of KTUS. Coverage more
likely near KSAD-KDUG-KOLS late this afternoon and evening. Gusty
outflow winds up to 40 kts possible with any thunderstorm.
Outside of thunderstorms winds in eastern terminals become east to
southeasterly after 31/16Z. East to southeast winds become common
late tonight. Aviation discussion not updated for TAF Amendments.

&&

.FIRE WEATHER...

Moisture increases east of Tucson today and across southeastern
Arizona Monday, with minimum relative humidity values above 20
percent becoming widespread Monday. Daily chances for
thunderstorms through this week with this increase in moisture,
with day to day variability. Gusty outflow winds possible with any
thunderstorm. East to southeast winds of 12-17 mph develop
Monday, potentially lingering through Tuesday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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