Flash Flood Warning 179, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
211 PM MST Wed Sep 2 2026

.SYNOPSIS...Scattered showers and thunderstorms continue this
afternoon into this evening, especially from Tucson southward.
Thursday into the weekend, elevated moisture continues with
scattered to numerous thunderstorms with the main threat being heavy
rainfall. High temperature will will fluctuate between normal and a
few degrees below normal.

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.DISCUSSION...Scattered thunderstorms have developed over the past
couple of hours, with the main area of convection from Tucson
southward. Most of the storms initially struggled with having
sustained updrafts, but we've been seeing some better storm
organization over the past hour or so, especially between Tucson and
Nogales. Main concern this afternoon into evening is locally heavy
rainfall resulting in isolated flash flooding with a secondary
threat of gusty winds to around 50 mph. Storm movement today is slow
(north-northeast about 5 to 10 mph) which will amplify the trend
towards those local areas of 1 to 2 inches of rain. While these
storms should diminish in scope during the evening hours, we'll
continue to keep an eye towards Sonora after midnight into the early
morning for potential MCS. This could push additional outflow or
even some overnight convection in our forecast area, especially
south of Tucson. The HRRR has latched onto this solution but the
other CAMs not as much, thus confidence is low but something we'll
be monitoring. Of course if late night convection were to occur or
remnants of an MCS pushing through Thursday morning, then leftover
clouds, subsidence or lower instability could reduce thunderstorm
chances Thursday afternoon.

Otherwise, more broadly speaking, we'll remain in an active pattern
Thursday/Friday and continuing into the weekend as lower level
southerly flow keeps reinforcing moisture from Sonora. Additionally,
the southerly flow will get some aid from Tropical Storm Marie (well
southwest of Baja) that will push additional moisture up the Gulf of
California towards southern Arizona. This will keep an above average
late monsoon pattern for us at least through the weekend with
primary threat continuing to be heavy rain with an isolated to
scattered flash flood threat. Note that the HREF shows this well for
Thursday with a 50% to 70% neighborhood probability (40-km) of 1" or
more in 3 hours across Santa Cruz, Ern Pima, far SE Pinal and
western Cochise Counties. There are no real well defined
disturbances/lift to really hone in on during this period for
southeast Arizona, so we'll continue to see day-to-day variability
in convection. Given the above normal moisture levels during the
period (PWAT averaging 1.3 to 1.7 inches), there will be higher than
normal chances for nocturnal convection, but confidence is quite low
on timing.

Elevated moisture levels look to continue early next week as well,
though the flow pattern become a bit more southeasterly at that
time.

Temperatures will be near or just slightly below normal through the
forecast period.

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.AVIATION...Valid through 04/00Z.
Expect SCT-BKN clouds 8-12k ft AGL through the forecast period.
Scattered SHRA/TSRA mainly from Tucson south and eastward continuing
through 03/04Z with slight chances of convection overnight into
Thursday morning. Additional SCT SHRA/TSRA once again mainly from
KTUS south and eastward aft 03/20Z. Near thunderstorms expect heavy
rainfall and gusty winds to 35 kts. Otherwise winds will be west
northwest 5-10 kts this afternoon and evening, and light and terrain
driven at other times. Aviation discussion not updated for TAF
amendments.

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.FIRE WEATHER...Expect scattered thunderstorms this afternoon into
evening mainly from Tucson south and eastward. Elevated storm
chances are expected Thursday into the weekend as above normal
moisture (aided by the tropics) moves in. Heavy rainfall leading to
flash flooding will be the main threat. Temperatures will be around
normal to a few degrees below normal into early next 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.

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.TWC WATCHES/WARNINGS/ADVISORIES...
None.

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