A dry lower atmosphere set the stage for thunderstorms capable of producing gusty outflow wind. An evening thunderstorm collapsed west of Casper generating a severe wind gust at Casper/Natrona County International Airport.
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The episode as NWS RIW wrote it up.
A dry lower atmosphere set the stage for thunderstorms capable of producing gusty outflow wind. An evening thunderstorm collapsed west of Casper generating a severe wind gust at Casper/Natrona County International Airport.
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 31, 7:10 PM MST, 1 hour 24 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 810 PM MDT WED AUG 31 2011 .UPDATE... RED FLAG CONDITIONS ARE ALLEVIATING THIS EVENING AS WINDS DIMINISH AND RH'S BEGIN TO RISE. THEREFORE THE RED FLAG WARNING HAS BEEN ALLOWED TO EXPIRE. .SHORT TERM...TONIGHT THROUGH SATURDAY WESTERN AND CENTRAL WYOMING WILL REMAIN BETWEEN A PACIFIC TROUGH OVER THE PACIFIC NORTHWEST AND A HIGH PRESSURE RIDGE OVER THE SOUTHERN PLAINS. THIS WILL CONTINUE TO PRODUCE SOUTHWEST FLOW ALOFT OVER WYOMING. AS THE PACIFIC TROUGH MOVES EAST...A COLD FRONT OVER SOUTHERN MONTANA WILL MOVE SOUTH INTO NORTHERN WYOMING TONIGHT AND SURGE SOUTH INTO CENTRAL WYOMING BY MORNING. THIS WILL BRING HIGHER HUMIDITY AND COOLER AIR TO NORTHERN AND CENTRAL AREAS AND BECOME A FOCUS FOR CONVECTION ON THURSDAY. SOUTH OF THE FRONT...DRY AND WINDY CONDITIONS WILL PERSIST. DRY AND STABLE AIR WILL THEN BE OVER THE AREA FRIDAY AND SATURDAY WITH WEST FLOW ALOFT PRODUCING BREEZY TO WINDY AREAS. MODELS IN FAIR AGREEMENT IN THE SHORT TERM. .LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY DRY CONDITIONS ASSOCIATED WITH AN AREA OF HIGH PRESSURE WILL LAST THROUGH MONDAY MORNING ACROSS THE FORECAST AREA WITH WARMING TEMPERATURES. THE RIDGE AXIS WILL THEN MOVE FURTHER EAST THROUGH THE FORECAST AREA...ALLOWING A SOUTHWESTERLY FLOW TO DEVELOP ACROSS MUCH OF THE CWA. THIS SOUTHWESTERLY FLOW WILL USHER IN ADDITIONAL MOISTURE MONDAY AFTERNOON...TO INTRODUCE SHOWERS AND THUNDERSTORMS...MAINLY ACROSS SOUTHWESTERN WYOMING. MODELS INDICATE THE POTENTIAL FOR AN AREA OF LOW PRESSURE TO FORMING OVER WYOMING TUESDAY NIGHT. THIS AREA OF LOW PRESSURE WILL THEN SWEEP ACROSS THE FORECAST AREA...SPREADING SHOWERS AND THUNDERSTORMS ACROSS THE AREA. COOLER TEMPERATURES WILL THEN REMAIN PRESENT OVER THE AREA. && .AVIATION... SHOWERS AND THUNDERSTORMS WILL CONTINUE THIS EVENING...ESPECIALLY ACROSS THE NORTHWEST WHERE STORMS WILL CONTINUE THROUGH THE OVERNIGHT HOURS. A COLD FRONT WILL MOVE THROUGH THE AREA OVERNIGHT AND INTO THE DAYTIME HOURS OF THURSDAY. BECAUSE OF THIS FRONT AND LINGERING MOISTURE FROM SHOWER ACTIVITY...MODELS INDICATE THE FORMATION OF A LOW CLOUD DECK AFTER 08Z THURSDAY FOR PORTIONS OF NORTHERN WYOMING...ESPECIALLY KCOD AND KCPR. CURRENT FORECAST SUPPORTIVE OF THESE LOW CLOUD DECKS. SCATTERED SHOWERS AND THUNDERSTORMS WILL THEN BE PRESENT ACROSS THE NORTHERN THIRD OF THE FORECAST AREA AFTER 12Z THURSDAY...WITH SHOWER ACTIVITY SPREADING SOUTH THROUGH THE DAY. PERIODS OF MVFR CONDITIONS WILL BE POSSIBLE UNDER HEAVY RAINFALL. GUSTY WIND WILL ALSO BE POSSIBLE WITH SHOWERS AND THUNDERSTORMS. && .FIRE WEATHER... CRITICAL FIRE WEATHER DAY FOR MUCH OF WESTERN AND CENTRAL WYOMING THIS EVENING. AN APPROACHING TROUGH WILL BRING VERY WINDY CONDITIONS ALONG WITH LOW RELATIVE HUMIDITY IN THE MID TO LOWER TEENS. RED FLAG WARNINGS ARE IN EFFECT FOR ALL AREAS EXCEPT 140...414...415 AND 416 FROM NOON UNTIL 8 PM THIS EVENING. EVEN THESE AREAS NOT IN THE WARNING WILL SEE THE STRONG WINDS...THOUGH RELATIVE HUMIDITY WILL BE SOMEWHAT HIGHER IN THESE ZONES. HOWEVER...THE FIRE WEATHER DANGER WILL BE QUITE HIGH. THUNDERSTORM COVERAGE WILL BE ISOLATED TODAY WITH STRONG OUTFLOWS AND LIGHTNING POSSIBLE. A COLD FRONT WILL MOVE INTO THE NORTH TONIGHT AND POSSIBLY INTO THE CENTRAL...EAST OF THE DIVIDE. GUSTY WINDS AHEAD OF THE FRONT WILL CONTINUE THURSDAY ACROSS THE WEST AND SOUTH...AND POTENTIALLY IN THE CENTRAL...AS THERE IS UNCERTAINTY INTO HOW FAR SOUTH THE FRONT PROGRESSES THURSDAY MORNING. FIRE WEATHER HIGHLIGHTS WILL LIKELY BE NEEDED OVER THE SOUTH AND POSSIBLY THE CENTRAL. THE TROUGH WILL MOVE ACROSS THE STATE THURSDAY AFTERNOON AND EVENING. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE ALONG THE FRONT. CHILLY AIR MOVES IN WITH AREAS OF FROST LIKELY OVER THE WEST FRIDAY MORNING. A CLIPPER SYSTEM MOVES ACROSS MONTANA FRIDAY...WITH WINDS INCREASING ONCE AGAIN. WITH VERY DRY AIR STILL IN PLACE...WILL SEE THE FIRE WEATHER DANGER REMAIN HIGH...ESPECIALLY SOUTH AND CENTRAL. && .RIW WATCHES/WARNINGS/ADVISORIES... RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING WYZ275>283-285>289-300. RED FLAG WARNING UNTIL 6 AM MDT THURSDAY WYZ284. && SHORT TERM...C.BAKER LONG TERM...BRANHAM AVIATION...BRANHAM FIRE WEATHER...C.BAKER
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 812 PM MDT WED AUG 31 2011 WYZ001>020-022>030-011200- ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST- BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS- EAST SWEETWATER COUNTY-FLAMING GORGE- GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS- NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN- NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS- ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES- SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN- SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY- TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN- UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN- WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST- YELLOWSTONE NATIONAL PARK- 812 PM MDT WED AUG 31 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...REST OF TONIGHT ISOLATED THUNDERSTORMS WILL BE ENCOUNTERED ACROSS THE WEST THIS MORNING AND ACROSS THE REST OF THE AREA THIS AFTERNOON AND EVENING. THE MAIN HAZARDS WITH THESE STORMS WILL BE STRONG OUTFLOW WIND GUSTS AND DANGEROUS LIGHTNING. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY THURSDAY...SCATTERED THUNDERSTORMS NORTH AND CENTRAL. SOME STRONGER STORMS ARE POSSIBLE. INCREASED FIRE DANGER SOUTH WITH STRONG...MAINLY DRY COLD FRONT PASSAGE. FRIDAY...INCREASED FIRE DANGER SOUTH AND CENTRAL DUE TO WARM TEMPERATURES...LOW RELATIVE HUMIDITY AND WINDY CONDITIONS. MONDAY...ISOLATED TO SCATTERED THUNDERSTORMS THUNDERSTORMS WEST. TUESDAY...ISOLATED TO SCATTERED THUNDERSTORMS. .SPOTTER INFORMATION STATEMENT... PLEASE REPORT ANY STRONG WIND GUSTS OR HAIL WITH THUNDERSTORMS. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 601 PM MDT WED AUG 31 2011 WYZ028>030-010130- EAST SWEETWATER COUNTY-FLAMING GORGE-ROCK SPRINGS AND GREEN RIVER- 601 PM MDT WED AUG 31 2011 SHOWERS AND THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER SWEETWATER COUNTY THROUGH 730 PM. THE STORMS AND SHOWERS WILL MOVE NORTHEAST THROUGH THE COUNTY. WIND GUSTS AROUND 45 MPH...BRIEF HEAVY RAIN...AND FREQUENT DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SMALL HAIL MAY OCCUR WITH STRONGER STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 637 PM MDT WED AUG 31 2011 WYZ002-003-010200- ABSAROKA MOUNTAINS-CODY FOOTHILLS- 637 PM MDT WED AUG 31 2011 A FEW SHOWERS AND THUNDERSTORMS WILL MOVE THROUGH NORTHEAST THROUGH THE ABSAROKA MOUNTAINS AND ACROSS THE LOWER ELEVATIONS OF PARK COUNTY THROUGH 800 PM. AREAS OF IMPACT WOULD INCLUDE WAPITI... CODY...CLARK...AND CHIEF JOSEPH HIGHWAY. WIND GUSTS AROUND 45 MPH...BRIEF HEAVY RAIN...AND FREQUENT DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SMALL HAIL MAY OCCUR WITH STRONGER STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 702 PM MDT WED AUG 31 2011 WYZ019-020-010300- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS- 702 PM MDT WED AUG 31 2011 A FEW SHOWERS AND THUNDERSTORMS WILL MOVE NORTHEAST FROM THE GREEN AND RATTLESNAKE MOUNTAINS ACROSS NATRONA COUNTY THROUGH 900 PM. THE MAIN AREAS THAT WILL BE IMPACTED WILL BE MUDDY GAP...MILLS AND CASPER...AND MIDWEST. INTERSTATE 25 FROM CASPER NORTH TO THE JOHNSON COUNTY LINE WILL ALSO BE IMPACTED AT TIMES. WIND GUSTS AROUND 55 MPH...BRIEF HEAVY RAIN...AND DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 742 PM MDT WED AUG 31 2011 WYZ028>030-010300- EAST SWEETWATER COUNTY-FLAMING GORGE-ROCK SPRINGS AND GREEN RIVER- 742 PM MDT WED AUG 31 2011 A FEW SHOWERS AND THUNDERSTORMS WILL MOVE NORTHEAST ACROSS SWEETWATER COUNTY THROUGH 900 PM. WIND GUSTS AROUND 45 MPH...BRIEF HEAVY RAIN...AND FREQUENT DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SMALL HAIL MAY OCCUR WITH STRONGER STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 902 PM MDT WED AUG 31 2011 WYZ019-020-010430- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS- 902 PM MDT WED AUG 31 2011 ANOTHER AREA OF SHOWERS AND THUNDERSTORMS WILL MOVE NORTHEAST FROM THE GREEN AND RATTLESNAKE MOUNTAINS ACROSS NATRONA COUNTY THROUGH 1030 PM. THE MAIN AREAS THAT WILL BE IMPACTED WILL BE MUDDY GAP... MILLS AND CASPER...AND MIDWEST. INTERSTATE 25 FROM CASPER NORTH TO THE JOHNSON COUNTY LINE WILL ALSO BE IMPACTED AT TIMES. WIND GUSTS AROUND 50 MPH...BRIEF HEAVY RAIN...AND DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 904 PM MDT WED AUG 31 2011 WYZ030-010400- EAST SWEETWATER COUNTY- 904 PM MDT WED AUG 31 2011 SHOWERS AND THUNDERSTORMS WILL MOVE NORTHEAST ACROSS EASTERN SWEETWATER COUNTY THROUGH 1000 PM. WIND GUSTS AROUND 45 MPH...BRIEF HEAVY RAIN...AND FREQUENT DANGEROUS LIGHTNING WILL OCCUR WITH MOST STORMS. SMALL HAIL MAY OCCUR WITH STRONGER STORMS. SEEK SAFE SHELTER INDOORS IF STORMS APPROACH YOUR LOCATION. AR
The Riverton/Lander radar (KRIW), 164 km away, was scanning. The volume nearest the first event began at 03:33 UTC.
1 thunderstorm wind. Local standard time, as filed.
A collapsing thunderstorm produced a 59 mph wind gust at Casper/Natrona County International Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2011Every state in 2011This day in weather historyWarnings in Wyoming, August 2011
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: 330287.