871
FXUS65 KTWC 182132
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
232 PM MST Mon Aug 18 2025

.SYNOPSIS...

Isolated to scattered thunderstorms this week across
Southeast Arizona, with day to day variability in intensity and
chances. The big story for Southeast Arizona will be the extreme
heat returning the second half of the week. An Extreme Heat
Warning is in effect Wednesday morning through Friday evening.

&&

.DISCUSSION...

In the upper levels, a broad ridge sits from the desert southwest
through the southern plains into the eastern CONUS. Over the
coming several days, the ridge center is forecast to shift west
and become over northern Arizona and northward through the Four
Corners region.

Today`s upper air observation out of Tucson has already seen the
impact of the westward transitioning ridge, with warmer
temperatures aloft decreasing the instability potential.
Precipitable water values over southeastern Arizona however,
particularly southern and eastern locations, remain healthy
enough for isolated to scattered convection today. Briefly heavy
rainfall and a very isolated strong wind gust possible with any
thunderstorm, but parameters for a notable wind or flooding threat
remain low.

Tuesday will see a northward surge of richer moisture, with the
12Z HREF showing high probabilities for 1.25 to near 1.5 inches of
precipitable water spreading across southeastern Arizona. This
should produce a greater coverage of afternoon/evening
thunderstorms, mainly from a line from Dudleyville-Tucson-Nogales
and east, however isolated coverage may push as far west as Sells.

Wednesday onwards sees a pattern of mean winds out of the east
pushing storms west, with higher quality moisture in western
locations. This is where we see daily chances (mainly in the 20-30
percent) range spread into western Pima county through Ajo. With
precipitable water values likely becoming drier in eastern areas,
this may be a pattern of thunderstorms with mainly wind threats
east of Tucson then becoming heavy rain threats as they move
westward. With the building ridge however thunderstorm coverage
through the second half of the week should become a bit more
isolated, especially east.

Arriving with the aforementioned building ridge will be a return
of above normal temperatures across southeastern Arizona. Highs
will range from 105-110 across desert locations of Pima and Pinal,
and 98-105 elsewhere. With highs exceeding 6 degrees above normal
in some areas and increasing HeatRisk, an Excessive Heat Warning
for Wednesday through Friday is now in effect.

Day to day thunderstorm chances through the weekend remain on the
lower end, mainly 15-30 percent at the highest (outside of the
White Mountains). However reasonable consistency exists in the
breakdown of the ridge and some western troughing early next
week, which would bring greater moisture and increasing
thunderstorm chances back into southeastern Arizona.

&&

.AVIATION...Valid through 20/00Z.

SCT-BKN clouds with isolated -SHRA/-TSRA mainly east/south towards
KSAD-KDUG-KOLS terminals. Light and terrain driven winds through
the forecast period with gusts up to 40 kts possible with any
thunderstorm today. Scattered thunderstorms likely to develop
Tuesday afternoon across much of southeastern Arizona. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...

Expect daily chances for thunderstorms and wetting
rain showers into next week. Min RHs will generally be 15-20
percent in the lower elevations and 20-30 in the mountains. Winds
will generally be less than 15 mph with typical afternoon gusts
up to 20 mph into next week. Temperatures will be trending above
normal the second half of this week, with extreme heat expected in
the lower elevations of Southeast Arizona.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Friday for
AZZ501>507-509.

&&

$$

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