Flash Flooding in Utah, September 6, 2002

Name: Flash Flooding in Utah, September 6, 2002
Start: 2002-09-06T17:30
End: 2002-09-06T19:30
Location: Utah

September 6, 2002 · NWS SLC · 2 events in 2 counties and zones

Heavy thunderstorm downpours produced localized flash flooding in Southern Salt Lake and portions of Utah counties. The rain produced a mudslide in Alpine, causing extensive damage to one home.

Where it happened

Every event with a place to put it; 2 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
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The toll

Deaths: 0
Injuries: 0
Property damage: $400,000
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 SLC wrote it up.

Heavy thunderstorm downpours produced localized flash flooding in Southern Salt Lake and portions of Utah counties. The rain produced a mudslide in Alpine, causing extensive damage to one home. About 20 homes in Pleasant Grove reported basement flooding. A canal above Bluffdale overflowed, sending a wall of water and mud into a subdivision, flooding at least 10 homes.

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 Salt Lake City, UT wrote its last area forecast discussion before the first event at Sep 6, 3:30 PM MST, 2 hours earlier.

Area forecast discussion, Sep 6, 3:30 PM MST, 2 hours before

UTAH AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
430 PM MDT FRI SEP 6 2002

.SYNOPSIS...A VERY MOIST AND SLIGHTLY UNSTABLE AIRMASS WILL BE OVER
THE GREAT BASIN THROUGH THE WEEKEND WITH TEMPERATURES GRADUALLY
COOLING.  DRIER AIR WILL MOVE INTO NORTHWEST SECTIONS SUNDAY.

.DISCUSSION...DEEP MOISTURE IN PLACE FOR MOST OF THE FORECAST AREA
THROUGH AT LEAST PART OF SUNDAY...AND RIPPLES IN THE UPPER FLOW
EJECTING OUT OF DEEP TROUGH ON THE WEST COAST. SEVERAL FACTORS WILL
DETERMINE THE EXTENT OF PRECIPITATION TONIGHT THROUGH SUNDAY. TWO
PRIMARY AREAS OF ACTIVITY SHOW UP IN THE ETA FOR THIS AFTERNOON INTO
THIS EVENING...ONE IS ASSOCIATED WITH A DISTURBANCE MOVING OUT OF
CALIFORNIA AND INTO NEVADA AT THIS TIME AND INITIATING THUNDERSTORMS
OVER NEVADA AND NORTHWESTERN UTAH. THIS AREA ALSO GAINING JET
SUPPORT FROM THE CORE EXTENDING NORTHEAST FROM NEAR RENO. THE OTHER
AREA IS IN EXTREME SOUTH CENTRAL UTAH ASSOCIATED WITH A FEATURE
MOVING THROUGH ARIZONA. OTHER AREAS JUST NOW STARTING TO FILL IN SO
WILL ONLY MAKE MINOR ADJUSTMENTS TO TONIGHTS PRECIPITATION COVERAGE
AND CHANCES ACROSS THE AREA. FAVORABLE LOW LEVEL SHEAR VECTOR ACROSS
MOST OF THE AREA SO MAY SEE SOME HEALTHY CELLS THIS AFTERNOON INTO
THIS EVENING...ESPECIALLY IN THE SOUTH AND NORTHWEST.

A NEW PLAYER IN SATURDAYS WEATHER IS TROPICAL DEPRESSION ELEVEN-E
NOW LOCATED NEAR 21N/111W. MODELS NOW BRING THIS NORTH A LITTLE
FASTER THAN PREVIOUS RUNS...REINFORCING MOISTURE OVER SOUTHERN UTAH
SATURDAY. LATEST FAN AND FWC POPS FOR CDC JUMPED DRAMATICALLY FOR
SATURDAY COMPARED TO PREVIOUS RUNS. REST OF THE AREA STAYS MOIST
SATURDAY WITH JUST THE EXTREME NORTHWEST CORNER OF UTAH DRYING OUT
SLIGHTLY. WITH UNCERTAINTY AS TO WHERE FAVORED AREAS OF CONVECTION
WILL SET UP...WILL LEAVE FORECAST FOR SATURDAY AS IS. JET TO OUR
NORTHWEST TAKES ITS TIME EJECTING OUT WITH THE POSITION OF THE RIGHT
REAR QUAD SATURDAY LIKELY TO ENHANCE ACTIVITY IN THE NORTHWEST AND A
LITTLE FARTHER EAST THAN TODAYS ACTIVITY.

AS WEST COAST TROF BEGINS TO SPLIT SUNDAY...LEAVING ONE PIECE WEST
OF BAJA AND EJECTING ANOTHER NORTH...ATMOSPHERE DRIES OUT IN WESTERN
SECTIONS SUNDAY WITH THE ONLY AREA OF DEEP MOISTURE REMAINING OVER
ROUGHLY THE SOUTHEASTERN THIRD OF THE AREA. WILL ADJUST POPS FOR
SUNDAY TO REFLECT THIS PATTERN. STILL ENOUGH MOISTURE FOR AT LEAST
CHANCE POPS ALL SECTIONS...SOME HIGHER.

FOR MONDAY THROUGH THE REST OF THE WORK WEEK...LATEST AVN IS NOW
HEADING TOWARDS THE LATEST UKMET AND ECMWF...KEEPING THE TROUGH THAT
THE MRF HAS BEEN BRINGING INTO THE WEST TO SUSTAIN A MOIST AND
DYNAMIC SOUTHERLY FLOW ALOFT THROUGH THE WEEK...AND INSTEAD HOLDING
IT BACK FARTHER WEST IN THE NORTH PACIFIC. THIS WOULD ALSO KEEP THE
SPLIT OFF PIECE OF THE CURRENT WEST COAST TROF FROM LIFTING NORTH ON
MONDAY. QUITE A BIT OF UNCERTAINTY NONETHELESS. THE UK/EC/AVN TREND
PUTS US IN A WEAK WESTERLY...AND DRIER...FLOW TUESDAY THROUGH
FRIDAY. THE SPLIT OFF PIECE MAY IN FACT DRIFT FARTHER SOUTHWEST AND
BE A NON FACTOR. HAVE DECIDED TO GO WITH THIS TREND AND REDUCE THE
COVERAGE OF PRECIPITATION THROUGH NEXT WEEK AND KEEP FRIDAY DRY.
BELIEVE IT OR NOT UKMET ACTUALLY LOOKS LIKE IT FLOATS REMNANTS OF TS
FAY...CURRENTLY IN GULF OF MEXICO...INTO THE SOUTHWESTERN STATES MID
WEEK.

SLC 4643  CDC 6653  JACKSON

.SLC...NONE.

The radar

The Salt Lake City radar (KMTX), 79 km away, was scanning. The volume nearest the first event began at 00:31 UTC.

Open the radar archive at this moment

Event by event

2 flash flood. Local standard time, as filed.

Flash Flood, Salt Lake

When: September 6, 5:30 PM MST to 7:30 PM MST
Where: Salt Lake County, Riverton
Property damage: $200,000
Reported by: GENERAL PUBLIC
Coordinates: 40.668, -111.924 (the zone’s center; the record gives no point)

Flash Flood, Utah

When: September 6, 5:30 PM MST to 7:30 PM MST
Where: Utah County, Alpine
Property damage: $200,000
Reported by: GENERAL PUBLIC
Coordinates: 40.120, -111.670 (the zone’s center; the record gives no point)

What these are

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

Every storm in Utah in 2002 Every state in 2002 This day in weather history Warnings in Utah, 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: 5324777, 5324778.