320
FXUS65 KTWC 201700
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
1000 AM MST Thu Aug 20 2026

.SYNOPSIS...Isolated to scattered afternoon and early evening
showers and thunderstorms will persist across Southeast Arizona into
the weekend. The primary concern with storms will be gusty outflow
winds, with a secondary concern for heavy rainfall mainly west of
Tucson where deeper atmospheric moisture will reside.
Otherwise, afternoon high temperatures will remain 5 to 8
degrees above normal through the weekend, with moderate to major
HeatRisk.

&&

.UPDATE...This morning the skies are clearing with heating to pick
up this afternoon. A sharp gradient in atmospheric moisture exists
from drier air moving in from the east/southeast yesterday. This is
evident on GOES total precipitable water imagery with values around
0.75 inches across Cochise County increasing to about an inch across
Santa Cruz, eastern Pima, eastern Pinal, Graham, and Greenlee
counties. Further west across central/western Pima and Pinal
counties values were in the range of 1.3 to 1.8 inches. As drier air
continues to nudge in from the east/southeast today, current
thinking is that storms will struggle, especially to the east and
south of Tucson where that drier air resides. Along and west of the
moisture gradient (or west and north of a Sells to Tucson to
Dudleyville line) is where the best chances (10-30%) will be
this afternoon. Convective allowing models are less bullish on
the coverage and severity of storm activity compared to
yesterday. That being said, any storms that do form could
produce strong gusty outflow winds (30-50% chance to exceed 35
mph), locally heavy rainfall, and small hail.

&&

.PREV DISCUSSION... /issued 134 AM MST Thu Aug 20 2026/

The upper pattern this morning is defined by large amplitude ridge
of high pressure over the Southwest with the high centered over
northern Arizona. The latest GOES precipitable water imagery
indicated PWATs in the eastern half of our CWA between 1.00 and 1.25
inches, with deeper moisture to the west between 1.25 and 1.75
inches. Drier air between 0.65 and 0.90 inches in Chihuahua Mexico
is begining to nudge into the extreme SE corner of the state with
the mid-level ELY/SELY flow. We will continue to see that deep plume
of moisture that was available for storms Wednesday wane and track
north and a drier easterly flow sets up. The upper high center today
will re- orient itself by elongating into central New Mexico. This
will focus an area of deformation/lift aloft across east-central and
northwest Arizona today instead of across our neck of the woods. So,
given the lower moisture and the lack of larger scale lift, we will
have to rely on the instability generated by strong insolation for
storm development resulting in generally weaker pulse-type storms.

The moisture across Southeast Arizona returns to near normal for
this time of year Friday into the weekend. As the upper ridge
becomes more neutrally oriented along the Rockies from NRN New
Mexico into central Colorado, we will see weak divergence in the
upper flow to the south and west of Tucson. Therefore, I would
expect a more typical primary concern for strong gusty outflow winds
across the majority of Southeast Arizona, with a secondary concern
for heavy rainfall SW/W of Tucson in the deeper moisture. The
Monsoon season rolls-on.

&&

.AVIATION...Valid through 21/00Z.
SCT-BKN 7-11k ft AGL BKN-OVC 12-15k ft AGL with scattered to
numerous -SHRA/-TSRA through 20/05Z. Gusty and erratic outflow winds
possible near TSRA with gusts to 40-50 kts. Organized outflows may
produce VSBY less than 1/2SM in BLDU, especially from KTUS west and
northwest. Winds outside of thunderstorms mainly light and terrain
driven. Tomorrow, scattered -SHRA/-TSRA return after 20/19Z.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Strong thunderstorms will return to Southeast
Arizona this afternoon. The primary concern with storms this
afternoon is that they will be capable of producing organized storm
outflow winds 45-55 mph, potentially producing localized dense
blowing dust. Deep moisture moving into the region from the Gulf of
California will bring about a secondary concern of heavy rainfall
capable of producing isolated flash flooding, especially across
central and eastern Pima county. Otherwise, an uptick in storm
strength and coverage into the upcoming weekend. Hot conditions will
persist this week with an Extreme Heat Warning in effect today
through Friday for portions of the Southeast Arizona. Winds mainly
light and terrain driven. Strong, gusty and erratic winds will
accompany thunderstorms. Minimum relative humidities 15-25 percent
in lower elevations with 25-35 percent in the higher terrain.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...

Extreme Heat Warning until 8 PM MST Friday for AZZ501-502-504>506-509.

&&

$$

DVS

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