522
FXUS65 KTWC 170850
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
150 AM MST Mon Aug 17 2026

.SYNOPSIS...Hot conditions return this week with temperatures
becoming 5 to 7 degrees above normal across Southeast Arizona.
An Extreme Heat Warning is in effect today through Friday for
portions of the area. Widely scattered to scattered
thunderstorms are expected to develop across Southeast Arizona
today. Dry air residing across the region will limit rainfall
amounts, but strong gusty winds 45-50 mph will be possible...
especially near the Gila River and San Simon valleys. Otherwise,
an uptick in thunderstorm coverage is anticipated the second
half of the week and into next weekend.

&&

.DISCUSSION...The upper pattern this morning is defined by a
ridge of high pressure centered over central Texas, a quasi-
stationary inverted trough near extreme WRN Texas/south-
central New Mexico and another high center near the northern
Baja. The latest GOES precipitable water imagery indicated a
dry-ish airmass across all of Southeast Arizona this morning,
with PWATs generally between 1.00-1.25 inches (drier values E
and SE of Tucson) and a pocket of deeper moisture (PWATs
1.25-1.50 inches) residing over NW Chihuahua Mexico.

Although it was a relatively quiet day with respect to thunderstorm
activity across Southeast Arizona Sunday (isolated storms along
the AZ/NM border), persistence isn`t always the best forecast
tool. That slow moving inverted trough to our east will begin to
track west today, moving into the ERN portions of Southeast
Arizona by 18/00Z this afternoon. As this happens, it will push
the upper-level high center near the northern Baja northward,
forcing it to become positively tilted by early this evening
from SW AZ up through central AZ. This movement will help
increase thicknesses values, with a couple of degrees of warming
over yesterday`s readings (6-10 degrees above normal) generally
west and northwest of Tucson. This co-incides with the portions
covered under the Extreme Heat Warning that takes effect today
and lasts through Friday.

With regards to convection, the lower precipitable water values
will generally limit the overall coverage of storms today despite
the mid-level inverted trough nudging into the area from the
east providing lift. The pocket of deeper moisture associated
with this disturbance will initially assist storm development
across the Gila NF of NM and the higher terrain of northern
Graham and Greenlee counties early this afternoon with the flow
then pushing storms SW into the valleys of Southeast Arizona.
Surface dewpoints are rather dry across the valleys, with
values early this morning in the lower to mid 50s. I would
expect the storms that drive into Graham and Cochise county
between 2 and 5 pm MST will be capable of producing strong
outflows of 45-50 mph due to evaporating downdrafts in the dry
sub-cloudy layer. This is supported by the 17/00Z HREF neighborhood
probability of storm outflows 35+ kts between 70-90 percent
across the Gila River and San Simon valleys at 18/00Z this
afternoon. I think the inherited PoPs from the NBM are too low
for today and had to nudge them up a bit in the official forecast,
especially with decent deformation in the flow aloft developing
along and just east of the upper ridge axis from the south-
central Pima into eastern Pima county. I am not expecting
widespread storms by any means, but I think widely scattered to
low-end scattered coverage seems reasonable. This includes the
Tucson Metro Area. The drier airmass will limit rainfall amounts,
but strong gusty winds to 45 mph are possible late this afternoon
into early this evening for central and eastern Pima county and
Santa Cruz county.

We should see a decrease in thunderstorm coverage Tuesday as
the upper high settles in over central Arizona. The remnants of
that inverted trough eventually exit the stage along the
International border. Decent shear associated with the feature
may result in stronger/more organized storms as they track
through south central and southwest Pima county Tuesday. As the
trough axis moves west of the Gulf of California, it will help
initiate a gulf surge of moisture northward into the lower
deserts of Southwest Arizona Tuesday night into Wednesday. The
combination of deeper moisture with a more favorable
thunderstorm pattern for Southeast Arizona Wednesday and
Thursday as the high center moves north into northern Arizona
will result in an uptick in thunderstorm coverage. This is
especially true as the high shifts near the Four Corners Friday
then northern New Mexico Saturday. Those two days at this time
have the appearance of being active...but during the Monsoon
season, a lot can quickly change with future potential patterns.

&&

.AVIATION... Valid through 18/12Z. FEW-SCT high level cirrus
through 17/20Z, then SCT-BKN 8-12k ft AGL BKN-OVC 12-15k ft AGL
with widely scattered to scattered coverage of -SHRA/-TSRA
through 18/04Z this evening. Gusty and erratic winds possible
near TSRA with gusts to 40-45 kts, especially in southern Graham
and northern Cochise counties including KSAD. Surface winds
light and terrain driven through early this afternoon, then
west to northwest 7-12 kts with occasional gusts to 20 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Hot conditions return this week with temperatures
becoming 5 to 7 degrees above normal across Southeast Arizona.
An Extreme Heat Warning is in effect today through Friday for
portions of the area. Widely scattered to scattered
thunderstorms are expected to develop across Southeast Arizona
today. Dry air residing across the region will limit rainfall
amounts, but strong gusty winds 45-50 mph will be possible...
especially near the Gila River and San Simon valleys. Minimum
relative humidities 15-25 percent in lower elevation areas this
week with 25-35 percent in higher terrain. Otherwise, an uptick
in thunderstorm coverage is anticipated the second half of the
week and into next weekend. Outside of thunderstorms, winds will
be terrain driven around 10 mph with occasional afternoon gusts
to 20 mph.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning from 10 AM this morning to 8 PM MST
Friday for AZZ501-502-504>506-509.

&&

$$

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