134
FXUS65 KTWC 151617
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
917 AM MST Sat Aug 15 2026

.UPDATE...Aloft high pressure is centered well to the east of
Louisiana putting southeast Arizona under southwesterly flow.
This has led to a decrease in moisture with GOES East total
precipitable water ranging from 1.25" in western Pima County to
0.95" along the AZ/NM border. Because of this expect just a
slight chance (10-25) percent for storms mainly south and east
of Tucson this afternoon and evening. Best chances will over
over the Sky Islands in Cochise County. Otherwise expect partly
cloudy skies and high temperatures a degree or two above normal.

Main update this morning has been upgrading the Extreme Heat
Watch to a Warning and extending it through Friday. High
pressure stays over the region most of next week leading to
areas of Major Heat Risk for Pima County, Pinal County, and
portions of Graham and Greenlee Counties. There is some
uncertainty in high temperatures next week Thursday and Friday
with easterly mid-level winds returning. However current model
runs are pessimistic with moisture return keeping PWATs around
normal or just below normal. So decided to extend the time
period through Friday.

&&

.SYNOPSIS...
Expect a slight chance of afternoon thunderstorms
today as the combination of drier-air and a more stable
atmosphere aloft will limit thunderstorm activity across
all of Southeast Arizona. Hot conditions will return late this
weekend with an Extreme Heat Watch in effect for portions of
Southeast Arizona Monday though Wednesday of next week. A more
active thunderstorm pattern returns the second half of next
week.

&&

.DISCUSSION...
The upper pattern this morning is defined by a
strong ridge of high pressure centered over Louisiana and a
broadening trough of low pressure along the West Coast. The
latest GOES precipitable water imagery indicated a much drier
airmass has positioned itself into Southeast Arizona, with PWATs
around an inch across Cochise county and around 1.25 inches
across the Tucson Metro and the lower deserts of Pima and Pinal
counties. Lower-level moisture still hanging-on a bit more than
expected primarily due to the recently saturated soils, with
surface dewpoints generally in the low to mid 60s. The exception
to the rule is across Graham and Greenlee counties with
dewpoints in the lower 50s. Although the will be a lack of
larger scale lift across the area, there may be enough moisture
for a slight chance of afternoon showers and thunderstorms.
There wont be much threat for widespread heavy rain today, but
with the drier mid-levels across the area, some of the storms to
do develop will be capable of producing localized gusty and
erratic winds to 40 mph.

The upper pattern over the next few days will become more
stable as the 500mb upper-high center slowly moves overhead by
Sunday and the 300mb high develops over the northern Baja. Weak
inverted trough near extreme NE Mexico will rotate toward our
neck of the woods this weekend, impacting the far SE portions of
AZ Sunday afternoon into Monday afternoon. Not too much
moisture around to work with, but we may see more thunderstorms
activity starting Sunday across Cochise county and along the
International Border.

The more impactful weather element in this forecast package will
involve the heat next week. With high pressure aloft, we will
see thicknesses increase enough to put portions of Southeast
Arizona in the major HeatRisk category with isolated pockets of
extreme. An Extreme Heat Watch in currently in effect from
late Monday morning through Wednesday evening. Although models
are still bullish with keeping the high center nearby, models
move the high center slightly north which will open Southeast
Arizona up to a more favorable easterly flow for thunderstorm
activity. Not only will this pattern result in a tad more
lower-level moisture to advect into the area from the east but
the possibility of more cloud cover may moderate surface heating
by a degree or two the second half of next week. For this
reason, we have decided to hold off on extending the Extreme
Heat Watch into next Thursday and Friday.

&&

.AVIATION /16Z SATURDAY THROUGH 16Z SUNDAY/...
Valid through 16/12Z. FEW-SCT clouds 12-15k ft AGL
BKN around 20k ft AGL through 15/20Z becoming SCT-BKN 8-12k ft
AGL BKN around 12-15k ft AGL. A slight chance of -SHRA/-TSRA
centered mostly over higher terrain through around 16/02Z.
Gusty and erratic winds possible near TSRA with gusts approaching
35 kts. Otherwise, SFC winds light and terrain driven through
midday, then NWLY at 7-12 kts with ocnl gusts to around 20 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...
A slight chance of storms this weekend focused
mainly south and east of Tucson and over the higher terrain. A
more active monsoon pattern looks to return around the middle of
next week. Minimum relative humidity will be 20-35 percent
today lowering to around 15-30 percent thereafter. Temperatures
will warm-up to above normal by Sunday and persist well into
next week. 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 Monday to 8 PM MST Friday for
AZZ501-502-504>506-509.

&&

$$

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