Heat in Arizona, August 15 to 19, 2025

Area Forecast Discussion
National Weather Service Tucson AZ
830 AM MST Fri Aug 15 2025

.SYNOPSIS...Isolated to scattered thunderstorms will initially
develop across Cochise county late this morning, becoming
scattered to numerous as they expand northwest toward the Tucson
Metro Area this afternoon. These storms will then build toward
the west and southwest late this afternoon into this evening as
deeper moisture in the lower deserts fuels additional storm
development. Given the ample atmospheric moisture available for
these storms, the main impact with the storms today will be the
potential for heavy rainfall, especially from Tucson south and
southeast. Otherwise, daily isolated to scattered showers and
thunderstorms will persist into next week with day to day
variability in intensity and chances.

&&

.UPDATE...Lingering showers from overnight continue this morning
east of Tucson. Showers will continue to dissipate into the late
morning. Isolated to scattered storms will begin early this
afternoon, around 1200 MST, starting areas south of Tucson
becoming more widespread extending into central Pima, western
Cochise, and southeastern Pinal counties by later this afternoon.
The main concern associated with these storms and showers is
locally heavy precipitation leading to flash flooding and
occasionally gusty winds with stronger storms. Due to significant
forecast PWATs around 1.4 to 1.6 inches and continual showers and
storms, the Weather Prediction Center (WPC) has placed eastern
Pima, western Cochise, and Santa Cruz counties in a slight risk
for excessive rainfall this afternoon. These storms and showers
will continue into the evening hours weakening to be just isolated
to scattered showers overnight.

&&

.PREV DISCUSSION... /issued 251 AM MST Fri Aug 15 2025/

.DISCUSSION...The performance of the 2025 Monsoon season has
generally been, *checks notes*, less than stellar for Southeast
Arizona so far. However, this may change a bit today as several
ingredients are present for the potential for heavy rainfall. The
main upper pattern this morning is defined by a trough of low
pressure across California, extending SE into WRN Arizona. As this
feature moves closer, we begin to see an area of speed divergence
aloft with a jet streak at 300 mb moving through areas east of
Tucson late this morning into early this afternoon. At 500 mb, the
approaching trough turns the flow clockwise over our CWA,
resulting in an area of deformation SE of Tucson around 15/18Z
expanding NW toward central Arizona by the afternoon. These two
features will assist thunderstorm development today. Initially,
isolated to scattered thunderstorms will develop across eastern
Santa Cruz and southern Cochise counties late this morning, with
storms expanding toward the Tucson Metro Area and increasing in
coverage (becoming numerous) into the afternoon. In addition to
the favorable environment for thunderstorm development to the east
of Tucson today, deeper lower-level moisture advecting north to
northeast through the lower deserts of SW Arizona this afternoon
will help fuel additional storm development toward the west and
southwest during the late afternoon and early evening due to the
lower-level moisture convergence. Given the ample moisture in
place across the region (GOES PWAT imagery indicating values
between 1.20 and 1.50 inches) we will see heavy rainfall across
portions of SW Cochise, Santa Cruz and eastern Pima county. Since
rainfall exceeding 0.75 inches is what it usually takes to see
running water in normally dry washes and roadway dips, along with
ponding of water in other low-lying and poor drainage areas...The
15/00Z NBM indicates a 15% probability of exceeding 0.75 inches in
Tucson today, along with a 30% probability of exceeding this
amount in Nogales and Sierra Vista. In fact, there is an 8%
chance of exceeding 1.00 inches at KTUS. The WPC has put the
aforementioned areas into the "slight" risk of exceeding flash
flood guidance within 25 miles of a given point in their Day 1
Excessive Rainfall Outlook (ERO) this morning.

The upper trough to our west will dry us out with the westerly
flow this weekend, especially Sunday. We should be able to
maintain enough moisture for isolated coverage/low-grade Monsoon
pattern Sunday into early next week. After that, we begin to see
the upper high center move back toward our neck of the woods,
eventually making its way to the Four Corners region by the middle
of next week. If, and that is a big if, we can import some deeper
moisture from the east-southeast into Southeast Arizona, we may
see a ramp-up in activity. However at this point, the deeper
atmospheric moisture may end up being a plume of higher
precipitable water values (1.50+ inches) moving up the Gulf of
California begining Tuesday, filling into the lower deserts once
again. Unfortunately, the main impact of the upper high moving
back into Arizona the second half of next week may be the
increase in afternoon high temperatures yet again. I don't believe
that anyone is excited about the chances of warming back up again
above 105 degrees.

&&

.AVIATION...Valid through 16/12Z. SCT-BKN clouds at 8-12k ft AGL
with scattered light -SHRA through 15/14Z. ISOLD-SCT -SHRA/-TSRA
will initially develop across Cochise and Santa Cruz (including
KOLS and KDUG) between 15/17Z-19Z, becoming SCT-NUM -SHRA/-TSRA
toward KTUS with occasional VSBY 3-5SM SHRA/TSRA with cigs BKN
5-8k ft AGL as they expand northwest toward KTUS aft 15/19Z. These
storms will then build toward the W/SW late this afternoon into
this evening as deeper moisture in the lower deserts fuels
additional storm development. Although gusty and erratic winds
35-40 kts will be possible near any TS, surface winds should
remain below 15 knots with the occasional afternoon gusts up to 20
kts. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Southeast Arizona will be in an active Monsoon
pattern today and Saturday, with the best chances for wetting
rain showers and thunderstorms occuring today. After Saturday,
there will be daily chances for thunderstorms and wetting rain
showers into next week. Min RHs will generally be around 25
percent in the lower elevations and 45+ percent in the mountains
today and Saturday. Sunday, min RHs will start to drop back down
to the 15-20 percent in the lower locations and 20-30 in the
mountains into the new week. Winds will generally be less than 15
mph with typical afternoon gusts up to 20 mph into next week.
Monsoon moisture is projected to return late next week to provide
higher chances for thunderstorms and rain showers. Temperatures
will be around normal through this weekend, trending above normal
the second half of next week.

&&

&&

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

Update...Malarkey

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