Flash Flood in Wyoming, August 26 to 27, 2002

Name: Flash Flood in Wyoming, August 26 to 27, 2002
Start: 2002-08-26T23:00
End: 2002-08-27T07:00
Location: Wyoming

August 26 to 27, 2002 · NWS RIW · 1 event in 1 county or zone

5 inches, along Murphy Creek in southern Johnson County. Also, rain gage measurements in excess of 4 inches were reported in this area.

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

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

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 RIW wrote it up.

A stationary thunderstorm brought flash flooding and doppler radar rainfall estimates of 7 to 7.5 inches, along Murphy Creek in southern Johnson County. Also, rain gage measurements in excess of 4 inches were reported in this area. Most of the rain fell between midnight and 4 AM MDT. A damage survey conducted by the National Weather Service Riverton office determined that Murphy Creek was at one point 300 yards wide and 20 feet deep near Lone Bear Road. This creek eventually compromised the safety of the northbound Interstate 25 bridge over Murphy Creek.

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 Riverton, WY wrote its last area forecast discussion before the first event at Aug 26, 2:05 PM MST, 8 hours 55 minutes earlier.

Area forecast discussion, Aug 26, 2:05 PM MST, 8 hours 55 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
230 PM MDT MON AUG 26 2002

THUNDERSTORMS ALREADY FIRING OVER THE BIG HORN BASIN AND ABSAROKAS,
WITH CONVECTION ALSO FIRING OVER WIND RIVERS AND WYOMING RANGE.  12Z
AVIATION IDENTIFIED NORTHERN AREA WELL BUT DID NOT HINT AT SOUTHERN
AND SOUTHWEST CONVECTION.  HOWEVER...AVN DOES PICK UP ON PCPN IN
CENTRAL WY OVERNIGHT THAT LOOKS PLAUSIBLE GIVEN CURRENT CONDITIONS.
GIVEN THIS DATA...WILL INCLUDE THUNDER IN ALL CENTRAL AND NORTHERN
ZONES...WITH WORDING FOR AFTER MIDNIGHT NEAR CASPER PER AVN TIME
CROSS SECTION BULLSEYE AROUND 10Z.

500 MB LOW OVER PACIFIC NW THROUGH PERIOD KEEPS CHANCE FOR
THUNDERSTORMS IN THROUGH THE WEEKEND.  UNFORTUNATELY DEEP MOISTURE
IS LACKING...SO HIGHER LIKELIHOOD OF MORE FIRESTARTS THAN DOUSING
EXISTING FIRES WITH RAIN...

.RIW...NONE.
JBS

The radar

The Riverton/Lander radar (KRIW), 187 km away, was scanning. The volume nearest the first event began at 05:59 UTC.

Open the radar archive at this moment

Event by event

1 flash flood. Local standard time, as filed.

Flash Flood, Johnson

When: August 26, 11:00 PM MST to August 27, 7:00 AM MST
Where: Johnson County, South Portion
Reported by: NWS STORM SURVEY
Coordinates: 44.039, -106.585 (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 Wyoming in 2002 Every state in 2002 This day in weather history Warnings in Wyoming, August 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: 5314328.