Severe Thunderstorm Warning 53, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
112 PM MST Mon Jul 20 2026

.SYNOPSIS...
The combination of ample moisture across Southeast Arizona and
an upper-level disturbance moving into the area from New Mexico
today will result in widespread showers and
thunderstorms, especially to the east and south of Tucson.
These storms will be capable of producing heavy rainfall. A
Flash Flood Watch is in effect for Graham, Greenlee, Cochise and
Santa Cruz counties this through Tuesday evening. Otherwise,
daytime temperatures will remain below average by several
degrees into midweek increasing to above normal late this week
into the weekend.

&&

.DISCUSSION...
Biggest change from this morning is extending the Flash Flood
Watch through tomorrow evening for Graham, Greenlee, Cochise,
and Santa Cruz Counties.

The main threat will be very heavy rainfall and flash flooding,
with gusty winds a secondary threat. There could be a localized
gust to 50 kts as convection moves off the terrain, but 30-40kts
are more likely. A deeper dive into the flash flood setup
shows abundant moisture and a susceptible area. Widespread
0.5"+ with localized amounts of 2"+ fell across a good chunk of
far SEAZ, especially Cochise County yesterday. This area will
be the most vulnerable. In addition, CAMs show weakly organized
clusters/single cell with the potential for cell mergers and at
least some training/backbuilding as flow remains relatively
weak. The best chance for training or backbuilding will be
across Cochise and Santa Cruz Counties this evening.

As the mid/upper level low noses into SEAZ from NM/MX,
convection could go well into the evening and perhaps into the
overnight. Confidence is low at this time regarding the
overnight, but there is at least some signal in the HREF of
higher rainfall totals across central Pima County. In addition,
at least some higher res solutions now show additional
convective development early morning across areas from Tucson
south to Nogales and west toward Sells. There still is not
enough confidence to expand the Flash Flood Watch west into
eastern/central Pima County, but its is not out of the question
we have a flash flood warning or two this evening or even
tomorrow morning.

As for the Tucson Metro, confidence is again low on the
evolution and propagation of storms off the rim this
evening/overnight. We will likely have storms in the metro, but
once again favoring the Catalina Foothills, Oracle/Catalina, the
far east side, and south into the Corona De Tucson. We cannot
rule out localized flash flooding, but probabilities are rather
low. The more likely scenario is seeing light to moderate rain
showers with embedded storms late evening into overnight/early
morning hours as the mid/upper level low begins to provide more
lift and elevated instability to the area.

Moving into Tuesday still remains a little tricky given how
active today will be and how convection lingers into tomorrow
morning, but enough CAMS, HREF probs of 3"+ amounts, and the
mid/upper level low moving across the CWA is more than enough to
bump up confidence. So the watch for tomorrow looks good, with
uncertainty remaining for areas along the watch in Pinal/Pima
County.

As we move into Wed/Thu/Fri, there should be a noticeable
downtrend in daily showers/storms. While it will trend drier,
there will still be daily convection, most likely favoring the
typical areas south and east of Tucson. The flash flood threat
will also lessen and allow for soils to recover as we heat up.
While the flash flood threat trends down, the threat for gusty
winds will increase with better mid and upper level flow/drier
air.

Monsoon activity looks to ramp back up for the weekend as the
high moves into a more favorable region and multiple waves look
to track across the area.

Daytime temps below average early this week, transitioning to
above average by midweek. Spotty major heat risk is possible for
portions of Pima County, generally around the metro and across
the western third of the county. In addition, the upper Gila
River Valley has some spotty major heat risk. As of now,
confidence is not high enough for an Extreme Heat Watch, due to
the limited coverage and possibility of monsoon activity/clouds
lowering aftn temps. We will monitor for now and message an
overall upward trend in temps and heat risk by mid week.

&&

.AVIATION /18Z MONDAY THROUGH 18Z TUESDAY/...
FEW/SCT cloud decks AOA 8-11k ft agl this afternoon, becoming
BKN/OVC as coverage of SHRA/TSRA expands through the evening.
KOLS/KDUG has the best chance to see TS with brief MVFR possible
under heavy +TSRA. Sfc winds generally less than 12kts, except
for around storms where VRB gusts to 40kts will be possible.

-TSRA/-SHRA continues into the evening and perhaps overnight
 with BKN/OVC decks lowering, but VFR will prevail.

&&

.FIRE WEATHER...
Daily chances for thunderstorms will continue each afternoon and
evening through the next 7 days with day to day variability.
Widespread showers and thunderstorms are expected east and south
of Tucson today, and again Tuesday. These storms will be capable
of producing heavy rainfall with the potential for flash flooding.
A Flash Flood Watch is in effect today/tomorrow for the eastern
portions of Southeast Arizona. Min RH 25-30% in the lower desert
locations and above 40% in the mountains through mid-week. By
Thursday into the weekend, RH could dip into the 17-22% range for
the lower deserts west of Tucson and the upper Gila River Valley
as temperatures warm to above average. Winds this week will
remain mainly light and under 15 mph, though strong and erratic
winds will be possible with any thunderstorm.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Tuesday evening for AZZ503-507>513.

&&

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