657
FXUS65 KTWC 182009
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
109 PM MST Tue Aug 18 2026

.SYNOPSIS...Hot conditions this week with an Extreme Heat Warning in
effect today through Friday for portions of the Southeast Arizona.
Isolated thunderstorms are expected today along and near the
International border in south-central and southwest Pima county. An
uptick in thunderstorm strength and coverage is anticipated the
second half of the week and into the upcoming weekend.

&&

.KEY MESSAGES...

-Extreme Heat Warning continues through Friday evening including
Pinal County, Tohono O`odham Nation, Tucson Metro Area, Upper Gila
River Valley, and Western Pima County.

-Increasing storm coverage and intensity expected for Wednesday and
Thursday across southeast Arizona with strong gusty outflow winds
the primary hazard along with locally heavy rainfall.

-Daily chances for afternoon showers and storms expected Friday into
the weekend as a favorable Monsoon continues for southeast Arizona.

&&

.DISCUSSION...Residual surface moisture in the region could help
moderate high temperatures this afternoon. However, the moisture
combined with above normal temperatures will make it feel like we
are a bag of steamed vegetables the next several days. Thus, we will
be continuing the Extreme Heat Warning which is valid through Friday
evening. There is a slight chance for showers and storms this
afternoon mainly over the White Mountains and areas west and south
of Tucson with a slight chance continuing across central and western
Pima County into the evening.

This afternoon and evening a surge of deeper moisture will seep into
areas west of Tucson supported by an inverted trough moving west
along the International Border today. This will prime the
environment for an uptick in storm activity for tomorrow and
Thursday. The mid/upper level high will be on the move over the next
few days ultimately becoming centered to our northwest tomorrow and
over the Four Corners on Thursday. The movement of the high will
help enhance rising motion by increasing deformation and diffluence
aloft.

Diving into a bit more detail utilizing the most recently available
high resolution guidance as of this writing, there appears to be an
elevated threat for storms capable of producing strong, gusty, and
erratic outflow winds as well as locally heavy rainfall on Wednesday
afternoon and evening. The 18/12Z run of the HREF depicts a 50-70%
chance for gusty outflow winds exceeding 35 mph, and even a slight
chance (5-15%) for gusts to exceed 55 mph. The Storm Prediction
Center (SPC) has included most of southeast Arizona in a marginal
risk for thunderstorms tomorrow capable of producing an isolated
severe wind gust or two which is consistent with the aforementioned
wind exceedance probabilities. Scattered showers and storms forming
around Noon MST tomorrow becoming widespread and perhaps more
organized later in the afternoon as they propagate west. This is
supported by deep layer shear (0-6 km) of around 20-25 kts and mean
storm motions of around 10-15 mph. As always, blowing dust becomes
an increasing concern with gusty outflow winds from stronger
thunderstorms.

The Weather Prediction Center (WPC) also has southeast Arizona in a
marginal risk for heavy rainfall that could result in isolated
instances of flash flooding. A surge of deeper moisture from the
Gulf of California resulting in rapid transition from a dry to wet
atmosphere over the next couple of days will result in an increasing
threat for flash flooding across western and central portions of
Pima County by Wednesday and Thursday. There is a 50-70% chance for
precipitable water to exceed 1.5 inches across central and western
portions of Pima County including Tohono O`Odham Nation tomorrow
afternoon which could support isolated instances of flash flooding
where storms remain slow/motionless or reform over the same areas.

Looking beyond today and tomorrow, chances showers and storms
continue again on Thursday (30-50%). Coverage and intensity of
storms Thursday will likely be dependent on the progression of
storms tomorrow. Friday into the weekend chances (10-30%) continue
each afternoon as we remain in a more favorable Monsoon pattern.

8 to 14 Day Outlook
Temperature: Likely Above Normal (60-80%)
Precipitation: Near Normal

&&

.AVIATION...Valid through 20/00Z.
FEW-SCT ceilings 8k-12k ft AGL after 18/20Z with slight chance of
-SHRA/-TSRA through 19/03Z. Gusty and erratic winds possible near
TSRA with gusts to 35-40 kts. Winds outside of thunderstorms mainly
light and terrain driven. More widely scattered thunderstorms
expected Wednesday afternoon and evening. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Hot conditions this week with temperatures 5 to 7
degrees above normal across Southeast Arizona. An Extreme Heat
Warning is in effect today through Friday for portions of the area.
Isolated thunderstorms are expected today along and near the
International border in south-central and southwest Pima county. An
uptick in thunderstorm strength and coverage is anticipated the
second half of the week and into the upcoming weekend. Winds mainly
light and terrain driven. Strong, gusty and erratic winds will
accompany thunderstorms. Minimum relative humidities 15-25 percent
in lower elevation areas this week with 25-35 percent in higher
terrain.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning until 8 PM MST Friday for AZZ501-502-504>506-509.

&&

$$

Discussion/Fire Weather...DVS
Aviation...Edwards

Visit us on Facebook, X, YouTube...and at weather.gov/Tucson