Name: Flash Flood and Hail in Arizona, September 12, 2022
Start: 2022-09-12T13:29
End: 2022-09-12T16:52
Location: Arizona

Where it happened

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Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 2

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS TWC wrote it up.

The remnants of tropical storm Kay were centered off the California coast but helped generate enough shear to produce severe thunderstorms that moved north across southeast Arizona during the afternoon and early evening. Large hail, heavy rain and flash flooding occurred in southwest Tucson.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Tucson, AZ wrote its last area forecast discussion before the first event at Sep 12, 1:00 PM MST, 29 minutes earlier.

Area forecast discussion, Sep 12, 1:00 PM MST, 29 minutes before

Area Forecast Discussion
National Weather Service Tucson AZ
100 PM MST Mon Sep 12 2022

.SYNOPSIS...Expect scattered to numerous showers and thunderstorms
through Tuesday. Thereafter, conditions start to dry out with a
large decrease in rain chances. Temperatures will be near to below
normal through the middle of the week, then increase to above normal.

&&

.DISCUSSION...Afternoon WV imagery shows a shortwave trough just off
the coast of northern Baja with a ridge near the AZ/NM border. This
places our CWA in broad southerly flow ahead of the trough (remnants
of TS Kay) which is gradually pushing east. Thunderstorms are off to
an earlier start than yesterday as the atmosphere setup favorably
with MLCAPE values up around 1500 J/KG. Combine that instability
with 25-30 kts of 0-6km bulk shear, lift from the incoming shortwave
and a stout dry slot nudging in and the threat for strong to severe
thunderstorms will continue this afternoon into early evening. Main
concerns will be strong winds and hail with the stronger storms.
Storm motions will generally be towards the north at around 20 mph
but with the potential for some training thunderstorms and an
already saturated ground from yesterday, flash flooding will pose a
threat as well.

Shower and thunderstorm activity will gradually diminish tonight but
we aren't out of the woods completely yet as the trough axis will
still be just west of our area Tuesday. Western areas will be dry
but enough moisture remains from Tucson eastward for scattered
showers and thunderstorms once again Tuesday afternoon.

Thereafter, dry westerly flow begins to dominate as moisture gets
shunted to our east. Still enough moisture for a chance of showers
and thunderstorms in the White Mountains but the rest of the
forecast area will be dry. A benign weather pattern with warmer
temperatures into the weekend and then we'll be watching for the
possible return for some moisture later in the weekend and into
early next week as the flow may become more southerly.

&&

.AVIATION...Valid through 13/12Z.
Expect numerous SHRA/TSRA to continue especially along and east of a
KTUS-KTUS line into the evening before diminishing overnight. Cloud
bases occasionally drop to around 5-8k ft AGL. Light and variable
surface winds shift SWLY/WLY 8-12 kts this afternoon, with possible
thunderstorm outflow winds of 40+ kts. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...A weather disturbance will pass through the state
through Tuesday, resulting in widespread rain chances. Locally heavy
rainfall will be possible with some of the stronger showers or
thunderstorms. A hotter weather pattern develops later in the week
as high pressure aloft strengthens over the region.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for AZZ503>515.

&&

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

The radar

The Tucson radar (KEMX), 52 km away, was scanning. The volume nearest the first event began at 20:30 UTC.

Open the radar archive at this moment

Event by event

1 hail, 1 flash flood. Local standard time, as filed.

Hail, Pima

When: September 12, 1:29 PM MST to 1:31 PM MST
Where: Pima County, 3.51 mi E of Tuscon Ryan Fld Arpt
Measured: 1 in hail
Reported by: Public
Coordinates: 32.130, -111.110

Flash Flood, Pima

When: September 12, 2:27 PM MST to 4:52 PM MST
Where: Pima County, 3.62 mi NE of Tuscon Ryan Fld Arpt to 1.39 mi E of Tuscon Ryan Fld Arpt
Cause: Heavy Rain
Reported by: Department of Highways
Coordinates: 32.160, -111.119

Heavy rain of 2-3 in 90 minutes caused flash flooding in southwest Tucson. Roads closed include Old Ajo Highway, Long Cast DR. and Iberia Ave.

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in Arizona in 2022 Every state in 2022 This day in weather history Warnings in Arizona, September 2022

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1058220, 1058230.