Severe Thunderstorm Warning 285, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
1200 PM MST Wed Sep 23 2026

.SYNOPSIS...There will be a chance of showers and thunderstorms
across much of southeast Arizona through Thursday, with the stronger
thunderstorms producing heavy rainfall and an isolated threat of
flash flooding. Drier air then overspreads southeast Arizona Friday
and Saturday. Moisture moves back into the area late in the weekend
into early next week, for a return of the chance of showers and
thunderstorms. High temperatures will be several degrees below
normal through Thursday, warming to within a couple of degrees of
normal over the weekend and then lowering back below normal
through the middle of next week.

&&

.DISCUSSION...The large scale pattern has a trough to our west
and high pressure aloft centered over northeast Mexico and Texas
through Thursday. A system will move across the northern tier of
states Friday and Saturday, pushing the upper high to the southeast
over the Gulf. A low pressure system and associated trough will then
move across California and the Great Basin early next week.

The flow across southeast Arizona between the trough to the west and
the upper high to the east remains southerly through Thursday. PWATs
of 1.0 to 1.25 inches across the forecast area today/tonight will
lower to near 1.0 inch Thursday. There will be a chance of showers
and thunderstorms from Sells eastward today, and mainly from Tucson
eastward Thursday. A disturbance tracking northward through central
Sonora will move into southeast Arizona late this afternoon/early
evening, helping to enhance shower and thunderstorm development. The
high resolution models mainly keep shower activity across the
eastern counties today, with the main bulk of thunderstorm
development through the evening hours tonight roughly in an area
bounded from Sierra Vista to Oracle westward to Sells. The stronger
thunderstorms through Thursday will be capable of producing heavy
rainfall and an isolated threat of flash flooding.

Drier air begins to overspread southeast Arizona from the west on
Friday, as the flows turns southwest/west in response to a system
tracking east across the northern tier of states. There will still
be a slight chance of showers and thunderstorms on Friday across far
eastern areas. However by Saturday, PWATs lower down to around 0.75
inches and convection should be shunted to our east across New
Mexico and southward into Sonora Mexico.

Sunday into early next week, the combination of an upper low/trough
moving into the West Coast and Hurricane Polo moving northward along
the Mexico coast will help spread moisture back across southeast
Arizona from the south. This moisture begins to move back into the
area on Sunday for a slight chance of showers and thunderstorms,
with deeper moisture moving in Monday and Tuesday and a chance of
showers and thunderstorms across most of southeast Arizona. The
track of Hurricane Polo remains uncertain once it reaches as far
north as Cabo. There is a near equal split in the models and
ensemble members turning the system west as those curving it east
into southern/central Sonora. The exact track will remain highly
dependent upon the timing/depth of the trough and position of Polo
when the trough moves into the west coast.

Behind the trough on Wednesday of next week there will be a slight
chance of showers and thunderstorms. This marks the official end to
the Monsoon Season (September 30). The moisture profile late next
week reflects the end of the monsoon, as high pressure aloft builds
over the eastern Pacific and Baja Peninsula and southeast Arizona
dries out significantly.

Overall, high temperatures will be several degrees below normal
through Thursday, warming to within a couple of degrees of normal
over the weekend, then lowering back below normal again through
the middle of next week.

&&

.AVIATION...Valid through 25/00Z.
West of KTUS, FEW-SCT clouds at 7k-10k ft AGL and SCT-BKN clouds AOA
15k ft AGL. East of KTUS, SCT-BKN clouds at 6k-9k ft AGL and BKN-OVC
clouds AOA 15k ft AGL. SCT -TSRA/-SHRA, slowly diminishing aft
24/05Z. ISOLD-SCT -TSRA/-SHRA developing again aft 24/17Z mainly
from KTUS eastward thru the end of the valid period. Mountain
obscurations, wind gusts to 40 kts and lowered VSBY with any -TSRA.
Outside of the thunderstorms, SELY/ELY winds at 10 kts or less.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...There will be a chance of showers and thunderstorms
across portions of southeast Arizona through Thursday. Drier air
overspreads southeast Arizona Friday and Saturday. Moisture then
moves back into the area late in the weekend into early next week,
for a return of the chance of showers and thunderstorms. High
temperatures will be several degrees below normal through Thursday,
warming to within a couple of degrees of normal over the weekend,
then lowering back below normal again through the middle of next
week. Minimum RH values will be in the 17-30 percent range from
Tucson westward through early next week, with values in the 28-40
percent range east of Tucson (even higher in the mountains). 20-foot
winds will be less than 15 mph through the upcoming weekend. Gusty
and erratic winds will be possible with any thunderstorm.

&&

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

&&

Zell

Visit us on Facebook, X, YouTube, and at weather.gov/Tucson