Severe Thunderstorm Warning 271, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
1233 PM MST Sun Sep 13 2026

.SYNOPSIS...An active week ahead with daily chances of showers
and thunderstorms. Elevated precipitation chances Monday with a
Flash Flood Watch for portions of southeast Arizona. Daily
high temperatures will fluctuate between near normal and a few
degrees below normal.

&&

.DISCUSSION...The calendar shows mid September but still no
transition to drier non monsoonal weather for the upcoming work week
as deep layer southerly flow continues. Moisture levels remain quite
elevated today with PWAT values ranging from 1.3 to 1.7 inches
(lowest near the NM border and highest west of Tucson). These values
are about 150 to 200 percent of normal and with the southerly flow
remaining this week, the above normal moisture isn't going anywhere.
Now with the abundant moisture in place, we start looking for other
atmospheric signals for more active days. The sun angle in September
certainly isn't as good now compared to July or August so it's
really helpful to have other upper level support for better storm
chances. Not much upper level support for today, though isolated to
scattered showers and thunderstorms will continue through the
afternoon into early evening mainly from Sells eastward. Heavy rain
will be the main threat.

Monday is shaping up to be a more active day. While we can't rule
out a bit of morning convection, HREF/REFS/UofA WRF-HRRR are leaning
to a more active afternoon into evening as the combination of a
ample instability (MLCAPE 1000-2000+ J/KG) and some modest
mid/upper level support result in more widespread shower and
thunderstorm chances. Given the anomalously high moisture and broad
wetter antecedent conditions over the past few days it won't take as
much rain for to get notable responses in our washes and rivers. The
HREF has a large 50 to 90 percent area of 1 inch or greater of rain
(40-km neighborhood probability) from Tucson eastward with about 10
percent for 2 inches of more. Given the increasing confidence for
scattered to numerous thunderstorms Monday and heavy rain potential
along with previously mentioned wet antecedent conditions, decided
to hoist a Flash Flood Watch from late Monday morning through Monday
evening on a line from Sasabe-Eloy eastward but excluding the White
Mountains where the setup isn't as favorable up there.

Beyond Monday, it's looking like an active week. Tuesday will likely
be a bit more down compared to Monday, though still will have
isolated to scattered showers and thunderstorms. Wednesday into
Thursday are looking like another up period with some enhancement of
a disturbance coming in from the south. Westerly flow aloft tries to
establish itself Friday into next weekend which should result in
decreasing precipitation chances especially from Tucson westward but
still plenty of time to sort out those details.

Temperatures this week will range from near normal to up to a few
degrees below normal.

&&

.AVIATION...Valid thru 15/00Z.
SCT-BKN clouds 8k-10k ft AGL with ISOLD-SCT SHRA/TSRA thru 14/04Z.
Can't rule out ISOLD SHRA/TSRA overnight into Monday morning but
confidence low. Scattered to locally numerous SHRA/TSRA expected to
develop aft 14/18Z and continue thru end of valid pd. SFC winds
SWLY/WLY 5-10 kts thru 14/04Z then terrain driven less than 10 kts
thru 13/16z. SLY/SWLY SFC winds 6-12 kts resume aft 13/16Z thru end
of valid pd. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...An active week ahead with daily chances of
showers and thunderstorms. High temperatures will fluctuate
between near normal and a few degrees below normal. Min RH
values mainly 20 to 45 percent in the valleys and 35 to 65
percent in the mountains over the next week. RH recoveries will
continue to be excellent overnight. Winds will generally remain
less than 15 mph and terrain driven. Gusty and erratic winds
will accompany thunderstorms.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Monday morning through Monday evening for
AZZ503>509-511>514.

&&

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