Severe Thunderstorm Warning 249, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
132 AM MST Mon Aug 31 2026

.SYNOPSIS...Expect scattered shower and thunderstorm activity
early this morning, brief break mid-morning, then another round
of scattered storms this afternoon and evening. Storm chances
and coverage decease Tuesday and Wednesday, then increase again
Thursday into the weekend. High temperature will be below
normal to start the week then near normal Wednesday into the
weekend.

&&

.DISCUSSION...Current radar shows scattered thunderstorms east
of Tucson with a few isolated storms west and north of Tucson
over Pinal County and central Pima County. The latest HRRR run
seems to be handling the convection east of Tucson well, but
does not show any of the convection west and north of Tucson.
These storms are likely being aided by a weak shortwave moving
through central Arizona. Storms east of Tucson will likely keep
moving north and produce moderate to heavy rainfall. At this
moment it is uncertain if Tucson will see any storms, there are
a couple outflows heading towards the metro from the east as
well as the north. This could kick off storms over the metro,
but confidence is low. This activity will likely continue
through the early morning, then a brief break or reduction in
coverage by mid to late morning. CAMs are showing another round
of scattered storms forming this afternoon and evening, but
activity from this morning could delay initiation and reduce
coverage or change where storms form. Still some uncertainty in
the forecast, but the threat is there for scattered convection.
Heavy rainfall leading to flash flooding looks to be the main
threat with strong to severe wind gusts a secondary threat. For
this afternoon and evening hi-res guidance is favoring areas
west of Tucson over the Tohono O'Odham Nation. Because of this
the Flash Flood Watch has been extended west of Tucson through
10 PM today.

After today moisture values decrease some thanks to southwest
flow aloft ahead of trough over the west coast. The ridge will
be centered well to the east. The upper air pattern will remain
like this through the work week. Expect a downturn in monsoon
thunderstorm activity and coverage Tuesday and Wednesday with
isolated storms mainly south and east of Tucson. High
temperatures will be 2-6 degrees cooler than normal today into
Wednesday.

Down in the tropics the NHC is monitoring a tropical wave with
disorganized showers and thunderstorms well south of SW Mexico.
This will likely become the next named eastern Pacific tropical
storm in a couple days. Models bring this tropical system north
along the west coast of Baja late in the work week into the
weekend. Still fairly large differences in how close to the
coast the center will be. However there is growing confidence
that it will send tropical moisture up to southeast Arizona.
PWATs begin to increase as early as Thursday and could reach as
high as 2" over far western Pima County by this weekend. This
far out still hard to pin down exact impacts from this potential
increase in moisture, but do expect an increase in thunderstorm
coverage and chances as early as Thursday, continuing into the
weekend.

&&

.AVIATION...Valid through 01/12Z.
SCT -SHRA/-TSRA east of KTUS through 31/14Z with KDUG and KSAD
the main terminals impacted. Storms may form from outflows
moving into the Tucson metro this morning, but confidence is too
low to put mention of thunder in the TAF. Brief break in
convection later this morning then storm chances return to the
area after 31/20z through 01/04Z. Expect BKN cigs 7k-12k ft AGL
for most of the period. Outflow SFC winds near TSRA 30-40 kts
otherwise SFC winds mostly less than 10 kts and terrain driven.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Expect scattered showers and thunderstorms this
morning continuing into the afternoon and evening today. Storms
will be capable of strong to severe wind gusts and heavy
rainfall. Storm chances and coverage decrease Tuesday and
Wednesday with activity mainly from Tucson south and eastward.
Then expect another increase in storm chances Thursday into the
weekend. Temperatures will be around normal today through the
coming work week. Minimum relative humidity values mainly 20 to
45 percent in the valleys and 30 to 60 percent in the mountains
over the next week. Winds will generally remain less than 15 mph
and terrain driven through the week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for AZZ502.
Flood Watch until 5 AM MST early this morning for AZZ503>507-
513>515.

&&

Hardin

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