Thunderstorms over the Owl Creek Mountains moved off the higher terrain and into a favorable environment to produce gusty outflow wind west of Thermopolis.
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The episode as NWS RIW wrote it up.
Thunderstorms over the Owl Creek Mountains moved off the higher terrain and into a favorable environment to produce gusty outflow wind west of Thermopolis.
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 Sep 16, 10:35 AM MST, 3 hours earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 1135 AM MDT SUN SEP 16 2012 .SHORT TERM...TODAY THROUGH TUESDAY NIGHT AN ELONGATED UPPER TROUGH EXTENDS FROM HUDSON BAY TO THE OREGON COAST EARLY THIS MORNING. A SHORTWAVE TROUGH MOVING THROUGH THE FLOW IS BRINGING SOME CLOUDS AND WEAK RADAR RETURNS TO SOUTHERN MONTANA AND NORTHWEST WYOMING AHEAD OF A COLD FRONT ASSOCIATED WITH THIS SHORTWAVE. CRITICAL FIRE WEATHER CONDITIONS ARE EXPECTED ONCE AGAIN TODAY SOUTH OF THE FRONT WHERE MAX HEATING CAN OCCUR AND DRY WESTERLY WIND CONTINUES. THE FRONT WILL MOVE SOUTHWARD TODAY AND SHOULD REACH THE CONTINENTAL DIVIDE BY ABOUT NOON. IF THE FRONT SHOULD SLOW DOWN...AREAS FARTHER NORTH COULD MIX DOWN THE WESTERLY WIND PRIOR TO FROPA. THE FRONT WILL BRING COOLER TEMPERATURES AND A SHIFT TO NORTHERLY WIND. SOME MOUNTAIN SHOWER ACTIVITY IS POSSIBLE IN THE WAKE OF THE FRONT WITH SOME LIGHT SNOW POSSIBLE ABOVE 10000 FEET IN THE CENTRAL AND NORTHERN MOUNTAINS. A CLAP OF THUNDER OR TWO CANNOT BE RULED OUT DURING THE AFTERNOON AND EVENING HOURS BUT MARGINAL LAPSE RATES AND LACK OF INSTABILITY WILL WORK TO KEEP THUNDERSTORMS AT BAY. WINDY CONDITIONS WILL CONTINUE BEHIND THE FRONT THROUGH THE EVENING HOURS. WIND SHOULD DECREASE OVERNIGHT AS THE SURFACE PRESSURE GRADIENT RELAXES A BIT AND NOCTURNAL BOUNDARY LAYER DECOUPLING CAN OCCUR. TEMPERATURES WILL BE COOLER THAN NORMAL MONDAY WITH DRY CONDITIONS PREVAILING. A FEW SHOWERS MAY LINGER IN THE BIGHORNS BUT SHOULD DISSIPATE BY NOON. WARMER BUT STILL DRY CONDITIONS ARE EXPECTED TUESDAY AS A LARGE RIDGE DEVELOPS OVER THE EASTERN PACIFIC BRINGING NORTHWEST FLOW TO THE INTERMOUNTAIN WEST. .LONG TERM...WEDNESDAY THROUGH SUNDAY GFS REMAINS FAIRLY CONSISTENT WITH ITS RUNS OVER THE PAST FEW DAYS WITH THE UPPER TROUGH OVER THE GREAT LAKES AND THE UPPER RIDGE OVER THE WEST COAST. THIS PUTS NW FLOW OVER THE AREA WED THEN NNW FLOW OVER THE AREA THURS AND FRI. THEN THE GFS BRINGS THE UPPER RIDGE AXIS INTO THE GREAT BASIN FOR SAT AND NEXT SUNDAY WITH NW FLOW OVER WY. THE 00Z/16 GEM MODEL IS MORE IN LINE WITH THE GFS AFTER ITS 12Z RUN WHICH WAS QUITE DIFFERENT AROUND THE FRIDAY AND SAT TIMEFRAME WITH A BIG SHOT OF COLD AIR DIVING INTO THE CENTRAL PLAINS AND ALONG THE EAST SLOPES OF THE ROCKIES. THE 00Z/16 GEM DOES NOT SHIFT THE UPPER PATTERN MUCH TO THE EAST KEEPING A MORE NNW FLOW OVER THE AREA FRIDAY AND SATURDAY. THE 12Z/15 ECMWF ALSO HAD THIS BIG COLD PUSH. THE 00Z/16 ECMWF RUN IS STILL SHOWING THE COOLING BUT NOT QUITE AS COLD AS ITS PREVIOUS RUN. 00Z/16 GFSENSEMBLE MEAN HINTS AT THE COLD FRONT THURS NIGHT INTO FRIDAY WITH A MORE NORTH FLOW OVER THE AREA. THIS WILL NEED WATCHING OVER THE NEXT FEW DAYS. AS STATED PRIOR NIGHTS HIGH AMPLITUDE FLOW MUST BE WATCHED FOR WESTWARD DIGGING ENERGY. NOT SURPRISED TO SEE SOME MODEL DIFFERENCES CROPPING UP NOW. FOR THIS EXTENDED FORECAST PACKAGE WILL SIDE WITH A MIX AND INTRODUCE SOME COOLING FOR EAST OF THE DIVIDE FRIDAY BUT NOT GO HOG WILD. IT STILL LOOKS DRY WED THROUGH NEXT SUNDAY IN THIS FLOW PATTERN. TEMPS ON WED WILL BE A LITTLE COOLER EAST OF THE DIVIDE BEHIND THE COOL FRONT WITH WARM TEMPS WEST OF THE DIVIDE. THURSDAY LOOKS SLIGHTLY WARMER ALL AREAS. COOLER EAST OF THE DIVIDE FRIDAY WITH LITTLE CHANGE FOR THE WEST AND SOUTHWEST. THEN A LITTLE WARMER SATURDAY AND SUNDAY AT THIS POINT AS THE THERMAL RIDGE AXIS GETS A LITTLE CLOSER. BREEZY AREAS WED THROUGH FRIDAY FOR PARTS OF THE BIGHORN MOUNTAINS AND JOHNSON COUNTY DUE TO THE NNW FLOW GRADIENT. && .AVIATION.../18Z ISSUANCE/ A COLD FRONT WILL CONTINUE TO SWEEP SOUTH THROUGH THE FORECAST AREA TODAY. EXPECT WIND SHIFTS AT THE MAJORITY OF AIRPORTS...WITH MOST AREAS SEEING THE FRONT BY 04Z THIS EVENING. THIS FRONT WILL RESULT IN SOME SHOWERS WITH ISOLATED THUNDERSTORMS...ESPECIALLY ACROSS THE CENTRAL BASINS AND MOUNTAINS...ALONG WITH THE WESTERN VALLEYS AND MOUNTAINS. SHOWER ACTIVITY WILL WEAKEN THIS EVENING...THOUGH SOME LIGHT SHOWERS MAY CONTINUE ACROSS THE EASTERN THIRD OF THE FORECAST AREA THROUGH MUCH OF THE FORECAST PERIOD. AFTER THE FRONTAL PASSAGE...LIGHTER WIND IS ANTICIPATED ACROSS THE AREA. SMOKE FROM ONGOING WILDFIRES WILL CONTINUE TO PRODUCE SOME OBSCURATIONS THROUGH THE PERIOD. && .FIRE WEATHER... WARM AND DRY CONDITIONS WITH WESTERLY WIND WILL CONTINUE ACROSS SOUTHERN WYOMING TODAY AS A COLD FRONT MOVES INTO THE NORTH. THE FRONT SHOULD REACH THE CONTINENTAL DIVIDE BY ABOUT NOON. SHOULD THE FRONT HANG BACK A BIT...CRITICAL FIRE WEATHER CONDITIONS COULD SPREAD A BIT FARTHER NORTH THAN THE RED FLAG WARNINGS BUT THAT IS NOT EXPECTED. COOLER TEMPERATURES WILL BRING HIGHER HUMIDITY VALUES BEHIND THE FRONT BUT WINDY CONDITIONS WILL REMAIN WITH A SHARP SHIFT TO THE NORTH. WIND WILL DECREASE OVERNIGHT AS COLDER AIR SETTLES IN. A FEW SHOWERS AND PERHAPS A THUNDERSTORM OR TWO ARE POSSIBLE IN THE MOUNTAINS NORTH OF THE FRONT BUT ANY THUNDERSTORMS WILL BE VERY ISOLATED IN NATURE. DRY CONDITIONS WITH LIGHTER WINDS ARE EXPECTED MONDAY WITH WARMER TEMPERATURES FOR TUESDAY AS HIGH PRESSURE BEGINS TO BUILD BACK IN OVER THE AREA. && .RIW WATCHES/WARNINGS/ADVISORIES... RED FLAG WARNING UNTIL 7 PM MDT THIS EVENING WYZ277>279-289. && SHORT TERM...BERC LONG TERM...AR AVIATION...BRANHAM FIRE WEATHER...BERC
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 530 AM MDT SUN SEP 16 2012 WYZ001>020-022>030-171200- 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- 530 AM MDT SUN SEP 16 2012 ...RED FLAG WARNING FOR PORTIONS OF SOUTHERN AND CENTRAL WYOMING TODAY THROUGH THIS EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT WARM...WINDY...AND EXTREMELY DRY CONDITIONS WILL COMBINE TODAY ACROSS SOUTHERN WYOMING TO PRODUCE EXTREME FIRE BEHAVIOR. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 235 PM MDT SUN SEP 16 2012 WYZ005>007-162200- OWL CREEK AND BRIDGER MOUNTAINS-SOUTHEAST BIG HORN BASIN- SOUTHWEST BIG HORN BASIN- 235 PM MDT SUN SEP 16 2012 SHOWERS AND THUNDERSTORMS MOVING INTO THE BIG HORN BASIN THIS AFTERNOON ARE PRODUCING SIGNIFICANT WIND. THESE STORMS WILL CONTINUE INTO THE EARLY EVENING HOURS. GUSTY WIND TO 55 MPH WILL BE POSSIBLE WITH STORM ACTIVITY. BRANHAM
The Riverton/Lander radar (KRIW), 65 km away, was scanning. The volume nearest the first event began at 20:36 UTC.
1 thunderstorm wind. Local standard time, as filed.
An individual with an automated wind sensor reported a thunderstorm wind gust of 72 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2012Every state in 2012This day in weather historyWarnings in Wyoming, September 2012
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: 410057.