646
FXUS65 KTWC 162106
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
206 PM MST Wed Sep 16 2026

.SYNOPSIS...
A weather system moving in from northern Mexico
today will bring widespread showers and thunderstorms into
Thursday morning which will be capable of producing heavy
rainfall. Drier conditions move in Friday limiting the daily
chance through this weekend into early next week. High
temperatures will be below normal today and Thursday, then be
around normal Friday into early next week.

&&

.DISCUSSION...
A tropical low has moved inland into Mexico SW of Hermosillo
with an upper level low west of central Baja. We are also seeing
multiple embedded MCVs exiting Graham/Greenlee.

These features are setting the stage for a rather robust and
potentially significant day across Arizona. Latest CAMs have
varying solutions, but they all have some flavor of a broad
areal expansion of current showers/storms with intensification
through the rest of the afternoon. While we are seeing some
deeper level convection, much of this is fairly shallow as of
now. However these are very efficient rainfall producers due to
the highly anomalous PWATS and favorable tall skinny CAPE
soundings supporting a tropical regime. This environment, in
conjunction with deep warm cloud rain processes, is providing 1"
to nearly 1.5" rainfall rates in 15-30 mins. Would expect this
to continue and maximize as deeper convection begins to develop
around early afternoon. In fact, the low level circulation that
has moved inland into Mexico is showing renewed signs of
rapidly cooling cloud tops on satellite.

As this low pressure moves into southern AZ this afternoon,
expect coverage to increase with an increasing flash flood risk.
Given what we have seen this morning, high PWATS, saturated
grounds, and the Moderate Risk ERO, we could see some isolated
instances of significant flash flooding. Deciphering on exactly
where that could be is tricky, but there is some indication it
will follow the low pressure circulation and just north, NE and
east of the low. That would place portions of Santa Cruz,
central and eastern Pima, and Pinal COs in the track. This is
lining up well with the initial runs of the WoFS showing a high
probability of seeing 2" of rain west of Tucson in the next few
hrs. 90th percentile is showing widespread 1-2" with isolated
to scattered areas of 2-3". With what has already fallen, there
could even be some localized 4"+ rainfall amounts. However these
would be isolated in nature and be dependent on where they fall.

There could also be a trailing band of convection, which could
train over some areas this evening. This is supported by 12Z
HREF now showing a 30% contour of greater than 3 inches of rain
in 3 hrs. This signal is just west of the Tucson Metro aligned
well with radar trends and WoFS runs, but the 10% contours is
covering most of the CWA from Tucson west and north into central
AZ.

While the severe risk is low, we cannot rule out a wet
microburst or two with a few isolated gusts approaching 60 mph.
Otherwise, very heavy rain and flash flooding is the main
threat.

Thursday: Precipitable water remains elevated for this time of
year with a slight risk for excessive rainfall continuing east
and south of Tucson. Showers and storms that develop will still
have the potential for locally heavy rainfall, but without the
disturbance nearby there will be a lack of forcing to help aid
in higher rainfall rates like Wednesday.

Friday through Tuesday: Drier air finally begins to filter into
southeast Arizona as flow aloft shifts more
westerly/southwesterly. This could help limit thunderstorm
activity somewhat and keep activity mainly east and south of
Tucson. High temperatures return to at or slightly above normal.

8 to 14 day outlooks (Wed Sep 23 to Tue Sep 29)
Temperature: Leaning above normal, 39-42% chance
Precipitation: Leaning above normal, 39-42% chance

&&

.AVIATION /20Z WEDNESDAY THROUGH 20Z THURSDAY/...
Valid thru 17/18Z. SCT-BKN clouds 7k-11k ft. This afternoon and
early evening, SCT-NUM SHRA/TSRA thru end of valid pd. VSBYS nr
1 SM at times with SHRA+/TS. Gusty and erratic outflow winds to
around 35-45 kts nr strongest TS. Outside of TS, SFC winds
SLY/SE at 7-12 kts. Drier conditions expected tomorrow as
activity shifts east of Tucson tomorrow. Aviation discussion
not updated for TAF amendments.

&&

.FIRE WEATHER...
A weather system moving in from northern Mexico
today will bring widespread showers and thunderstorms into
Thursday morning which will be capable of producing heavy
rainfall. Drier conditions move in Friday limiting the daily
chance through this weekend into early next week. High
temperatures will be below normal today and Thursday, then be
around normal Friday into early next week. 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.

&&

.HYDROLOGY...
Heavy rainfall over the last 24 to 72 hours has resulted in
saturated soils and flowing streams/washes across southeast
Arizona. Upon collaboration with the Colorado Basin River
Forecast Center, an additional 1 to 2 inches could result in
rises that could cause some locations to exceed action stage
and approach minor flood stage. This will be dependent on where
the rain falls and how it interacts with each basin. Some areas
we are closely monitoring are portions of the Gila around Duncan
to Solomon, which could approach action stage with a second
round of rain this evening. Brawley Wash, Pantano Wash, and
Sabino Creek could also approach action stage and even minor
flood stage at Sabino given rainfall amounts of 1-2" in the
basin on a 2 hr period. These areas could come into play by this
evening. Will be monitoring these sites in coordination with
the RFC closely for potential impacts and update as necessary.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 11 PM MST this evening for AZZ501>515.

&&

$$

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