Flash Flood and Hail in Arizona, September 10, 2002

Name: Flash Flood and Hail in Arizona, September 10, 2002
Start: 2002-09-10T14:30
End: 2002-09-10T19:00
Location: Arizona

September 10, 2002 · NWS TWC · 4 events in 1 county or zone

A severe thunderstorm developed over the greater Tucson area producing damaging winds, hail, and flash flooding. 5 inches in diameter at the University of Arizona to one inch in diameter across Tucson and Marana.

Where it happened

Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $64,000
Crop damage: None recorded
Events: 4

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.

A severe thunderstorm developed over the greater Tucson area producing damaging winds, hail, and flash flooding. Hail size ranged from 1.5 inches in diameter at the University of Arizona to one inch in diameter across Tucson and Marana. A spotter in central Tucson recorded a peak wind gust of 60 mph and the ASOS at the Tucson International Airport recorded a peak wind gust of 54 mph. The strong winds also knocked down a power pole which left 2300 customers without power. The winds also overturned a mobile home located on Old Vail Road. There was also widespread flash flooding, with rainfall rates of greater than a half of an inch in 30 minutes. Several roads were closed due to flooding which included Sahuarita, Overton and La Cholla roads at Canada del Oro wash, and Davidson.

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 10, 2:30 PM MST, 0 minutes earlier.

Area forecast discussion, Sep 10, 2:30 PM MST, 0 minutes before

SOUTHEAST ARIZONA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
230 PM MST TUE SEP 10 2002

.SYNOPSIS...THE SLOW MOVING LOW PRESSURE SYSTEM NEAR SAN DIEGO WILL
FINALLY MOVE NORTHEAST AND OUT OF THE AREA BY FRIDAY. THE LOW
PRESSURE WILL PRODUCE THUNDERSTORMS STATEWIDE TONIGHT AND WEDNESDAY.
ON THURSDAY...THUNDERSTORMS WILL BE MOVING EASTWARD AND THEN OUT OF
THE STATE BY THE WEEKEND. THIS WILL ALLOW TEMPERATURES TO WARM TO
SEASONAL NORMALS AND HUMIDITY TO DROP.

.DISCUSSION...ACTIVE THUNDERSTORM DAY...WITH UNIDIRECTIONAL FLOW
SHOULD GET SOME SPLITTING STORMS...BUT ITS IFFY ALOFT FOR LARGE
HAIL SINCE H5 TEMPS ARE ONLY -7C...ALTHOUGH THEY MAY GET COLDER THIS
AFTERNOON. UPPER LEVEL DRY AIR WILL RESULT IN A LOT OF ENTRAINMENT
OF DRY AIR SO THERE SHOULD BE SOME VIGOROUS VERTICAL MOTIONS...ALL
SAID PRESENT WORDING FOR AFTERNOON CONVECTION OF NEAR SEVERE LOOKS
PRETTY GOOD. THERE WILL PROBABLY BE SOME CONVECTION ALL NIGHT LONG
AS UPPER LOW SWINGS OUT AND DRAWS ELEVATED CAPE INTO THE AREA. HARD
TO TELL WHERE THAT WILL BE. QUICK MOTION OF THE STORMS LOWERS ANY
POTENTIAL FOR FLASH FLOODING.

TOMORROW IT WILL BE WARMER ALOFT WITH LESS DYNAMICS ALTHOUGH STILL
ENOUGH MOISTURE FOR STORMS. STORMS SHOULD ALSO MOVE A TAD SLOWER SO
POTENTIAL FOR FLASH FLOODING GOES BACK UP A LITTLE. BY THURSDAY DRY
AIR WILL CONFINE MOST STORMS TO THE MOUNTAINS AND EASTERN ZONES.
THEN ONLY ISOLATED ON FRIDAY. NORTHWEST FLOW FOR THE WEEKEND WILL
CONTINUE THE DRYING BUT NOT LET US GET TOO HOT...JUST NEAR NORMAL.

.TWC...NONE.

In the hours before

Special weather statement, Sep 10, 1:50 PM MST, 40 minutes before

AZZ019-029>035-110700-

SOUTHEAST ARIZONA HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TUCSON AZ
150 PM MST TUE SEP 10 2002

.SYNOPSIS...AN AREA OF LARGE SCALE LIFTING ASSOCIATED WITH AN UPPER
LOW OVER THE NORTHERN BAJA WILL INTERACT WITH THE MOIST ATMOSPHERE
RESIDING ACROSS THE REGION TODAY RESULTING IN A MODERATELY ACTIVE
CONVECTIVE DAY ACROSS SOUTHEAST ARIZONA. THE PROBABILITY FOR
RECEIVING PRECIPITATION IN EXCESS OF ONE INCH WILL BE ABOVE
CLIMATOLOGY WHILE THE THREAT OF SEVERE WEATHER WILL BE NEAR OR
SLIGHTLY ABOVE CLIMATOLOGY.

.DISCUSSION...ITS SHAPING UP TO BE A MODERATELY ACTIVE AFTERNOON AND
EVENING ACROSS SOUTHEAST ARIZONA AS AN AREA OF LARGE SCALE ASCENT
ASSOCIATED WITH AN UPPER LOW OVER THE NORTHERN BAJA WILL INTERACT
WITH THE MOIST ATMOSPHERE RESIDING ACROSS THE REGION. THE WATER VAPOR
SATELLITE IMAGERY INDICATED AN AREA OF DRY AIR ALOFT WILL CONTINUE
TO PUSH EASTWARD INTO THE FORECAST AREA AS THE UPPER LOW BEGINS TO
LIFT NORTHEAST. ALTHOUGH AMPLE SURFACE HEATING WILL BE THE PRIMARY
FOCUSING MECHANISM FOR THUNDERSTORM DEVELOPMENT TODAY...THE
MOISTURE/DENSITY DISCONTINUITY ASSOCIATED WITH THIS DRY AIR WILL
ALSO SERVE AS A FOCUSING MECHANISM TO AID CONVECTIVE INITIATION.

THE STRONG NORTHWARD STORM MOTION...TOWARDS THE NORTH AT 20 MPH...
WILL SOMEWHAT LIMIT THE TIME ANY INDIVIDUAL STORM WILL RESIDE OVER A
PARTICULAR LOCATION. ALTHOUGH THIS WOULD NORMALLY LIMIT THE THREAT
OF FLASH FLOODING...THERE IS PLENTY OF LOW TO MID-LEVEL MOISTURE
AROUND FOR VERY HEAVY DOWNPOURS TO OCCUR. THEREFORE...THE
PROBABILITY FOR RECEIVING PRECIPITATION IN EXCESS OF ONE INCH WILL
BE ABOVE CLIMATOLOGY.

AS FOR SEVERE THUNDERSTORMS...THE COMBINATION OF THE THE UPPER LEVEL
FORCING ALONG WITH AMPLE SURFACE HEATING WILL ENHANCE CONVECTIVE
UPDRAFTS. HOWEVER...THE LOWER LEVELS REMAIN QUITE MOIST WHICH WILL
LIMIT THE THREAT FOR DAMAGING THUNDERSTORM WINDS. THEREFORE...THE
THREAT OF SEVERE WEATHER WILL BE NEAR OR SLIGHTLY ABOVE CLIMATOLOGY.

The radar

The Tucson radar (KEMX), 47 km away, was scanning. The volume nearest the first event began at 21:31 UTC.

Open the radar archive at this moment

Event by event

2 hail, 1 flash flood, 1 thunderstorm wind. Local standard time, as filed.

Hail, Pima

When: September 10, 2:30 PM MST to 3:30 PM MST
Where: Pima County, Tucson
Measured: 1.5 in hail
Reported by: NWS EMPLOYEE(OFF DUTY)
Coordinates: 32.233, -110.933

Flash Flood, Pima

When: September 10, 2:45 PM MST to 7:00 PM MST
Where: Pima County, Tucson
Reported by: LAW ENFORCEMENT
Coordinates: 32.097, -111.790 (the zone’s center; the record gives no point)

Thunderstorm Wind, Pima

When: September 10, 3:20 PM MST to 3:25 PM MST
Where: Pima County, Tucson
Measured: 60 kt (69 mph)
Property damage: $64,000
Reported by: GENERAL PUBLIC
Coordinates: 32.233, -110.933

Hail, Pima

When: September 10, 4:00 PM MST to 4:30 PM MST
Where: Pima County, Marana
Measured: 1 in hail
Reported by: TRAINED SPOTTER
Coordinates: 32.450, -111.217

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.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.

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

The same day elsewhere

Every storm in Arizona in 2002 Every state in 2002 This day in weather history Warnings in Arizona, September 2002

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: 5316889, 5316890, 5316888, 5316970.