An increasing pressure and temperature gradient between the Absaroka Mountains and Cody Foothills produced a brief period of high wind gusts southwest of Clark. Peak wind speeds were 60 and 62 mph around midnight December 20.
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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.
The episode as NWS RIW wrote it up.
An increasing pressure and temperature gradient between the Absaroka Mountains and Cody Foothills produced a brief period of high wind gusts southwest of Clark. Peak wind speeds were 60 and 62 mph around midnight December 20.
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 Dec 19, 10:45 PM MST, 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 1045 PM MST WED DEC 19 2012 .SHORT TERM...TONIGHT THROUGH SATURDAY CLEARING BEHIND THE EXITING TROUGH MAY CONTRIBUTE TO ANOTHER VERY COLD NIGHT ACROSS SOME OF THE BASINS AND VALLEYS TONIGHT. HOWEVER THERE WILL BE SOME MILDER AIR MOVING IN ALOFT THAT COULD MIX DOWN TO THE SURFACE IF THE WINDS END UP BEING STRONG ENOUGH...WHICH IS ALSO A POSSIBILITY GIVEN THE INCREASING SURFACE GRADIENT AND DOWNWARD FORCING SUPPLIED BY AN UPPER JET NOSING INTO THE REGION. THE AREAS THAT WILL LIKELY MIX WILL BE THE WIND CORRIDOR AND THE CODY FOOTHILLS...WHERE A HIGH WIND WATCH HAS BEEN UPGRADED TO A WARNING FOR TONIGHT FOR GAP FLOW COMING OUT OF THE ABSAROKAS. THE MODELS ARE STILL HANGING ONTO A VERY SHARP TEMPERATURE GRADIENT ALONG THE BARRIER...WHEN COMBINED WITH THE FORCING PROVIDED FROM THE JET ALOFT...A WARNING SEEMS TO BE APPROPRIATE FOR THE OVERNIGHT HOURS. HOWEVER...HIGH PRESSURE BUILDING INTO THE SOUTH FROM COLORADO WILL LIKELY KEEP A LID ON THE SOUTHERN BASINS AND VALLEYS...WHICH ARE ALSO NEWLY SNOW COVERED...SO KEPT TEMPERATURES BELOW ZERO FOR OVERNIGHT LOWS IN THE UPPER GREEN RIVER BASIN INCLUDING BONDURANT...PINEDALE AND BIG PINEY AS WELL AS FOR STAR VALLEY AND THE JACKSON VALLEY...IN FACT THE TEMPERATURES IN THE FORECAST ARE ON THE CONSERVATIVE SIDE AND THEY COULD DROP FURTHER IN THE TYPICALLY COLDER SPOTS IN THE WEST. THE WIND RIVER BASIN MAY BE A BIT MORE COMPLICATED AS IT IS CLOSER TO THE INFLUENCE OF THE JET AND IS ALSO MORE PRONE TO NORTHWEST FLOW. TEMPERATURES IN THE UPPER WIND RIVER BASIN WERE KEPT MILD...BUT LOWERED THEM A FEW DEGREES IN THE LOW SPOTS OF THE CENTRAL WIND RIVER BASIN WHERE MIXING IS NOT EXPECTED TO OCCUR. ANOTHER FACTOR TO CONSIDER WILL BE FREEZING FOG FORMATION IN THE CALM BASINS AS WARM AIR MOVES ATOP THE NEW SNOW...WHICH COULD KEEP SOME AREAS FROM BOTTOMING OUT...THIS FOG IS MOST LIKELY TO FORM IN THE UPPER GREEN RIVER BASIN AND PERHAPS INTO THE JACKSON VALLEY...STAR VALLEY AND SOUTHERN LINCOLN COUNTY. THE FLAMING GORGE AREA AND PORTIONS OF SOUTHWEST SWEETWATER COUNTY COULD ALSO HAVE SOME PATCHY FOG FORMING OVERNIGHT. EASTERN SWEETWATER COUNTY SHOULD BE TOO WINDY AS LEE SIDE TROUGHING INCREASES SOUTHWEST FLOW. RIDGING HOLDS ON FRIDAY WITH HIGH PRESSURE REMAINING OVER NORTHERN COLORADO AND LEE SIDE TROUGHING REMAINING OVER EASTERN WYOMING. HOWEVER THE INFLUENCE OF THE UPPER JET WANES A BIT ON FRIDAY SO WHILE WINDS WILL REMAIN GUSTY OVER THE HIGHER ELEVATIONS OF NORTHERN AND CENTRAL WYOMING...MOST OF THE WIND SHOULD REMAIN IN THE HIGHER ELEVATIONS. BREEZY CONDITIONS WILL REMAIN FROM ROCK SPRINGS TO CASPER THROUGH FRIDAY AS WELL. A TROUGH ALONG THE WEST COAST DIGS ON SATURDAY POSSIBLY SENDING OUT A SHORT WAVE AHEAD OF THE MAIN TROUGH...CROSSING THE WEST LATE SATURDAY AFTERNOON...BUT IT WILL NOT HAVE MUCH AFFECT ON THE REGION WITH ONLY A SLIGHT CHANCE OF SNOW IN THE NORTHWEST EXPECTED ON SATURDAY WITH CONTINUED MILD CONDITIONS EAST OF THE DIVIDE AS THE RIDGE AXIS BEGINS TO SHIFT EAST. .LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY ...SNOWFALL MAY IMPACT HOLIDAY TRAVEL SUNDAY THROUGH TUESDAY... DEVELOPING SOUTHWEST FLOW WILL ALLOW MOISTURE TO MOVE OVER THE WESTERN MOUNTAINS SATURDAY EVENING. THIS WILL BE THE BEGINNINGS OF WINTRY WEATHER...WHICH MAY CONTINUE OVER MUCH OF THE AREA THROUGH MONDAY. SATURDAY SNOWFALL IS EXPECTED TO BE GENERALLY LIGHT AS IT IS ASSOCIATED WITH A WEAKER DISTURBANCE. MOST SNOWFALL SHOULD BE CONFINED TO THE WESTERN MOUNTAINS...THOUGH SOME ACTIVITY OVER THE WESTERN VALLEYS IS NOT OUT OF THE QUESTION. MEANWHILE...A STRENGTHENING PACIFIC LOW PRESSURE SYSTEM BEGINS TO DIVIDE DOWN THE PACIFIC COAST...WITH ITS ASSOCIATED SNOWFALL SPREADING ACROSS PORTIONS OF THE WESTERN UNITED STATES. CONTINUED SOUTHWEST FLOW OVER THE FORECAST AREA WILL CONTINUE TO USE THIS MOISTURE TO GENERATE ADDITIONAL WESTERN SNOWFALL. AFTER DIVERGING FAIRLY SIGNIFICANTLY ON THE LAST MODEL RUN...THE GFS AND ECMWF HAVE COME TO A BETTER AGREEMENT REGARDING THE POTENTIAL WIDESPREAD SNOWFALL BEGINNING SNOWFALL SUNDAY NIGHT. A STRONGER PUSH OF MOISTURE ASSOCIATED WITH A WAVE OF LOW PRESSURE WILL SPREAD ACROSS THE FORECAST AREA THROUGH MONDAY MORNING...WITH SNOWFALL ANTICIPATED TO SPREAD EAST OF THE DIVIDE BY THE AFTERNOON HOURS. SNOWFALL WILL CONTINUE THROUGH CHRISTMAS EVE ACROSS MUCH OF THE AREA AS WAVE OF LOW PRESSURE STRUGGLES TO CLOSE OFF...BUT STILL DIVES SOUTH OF THE FOUR CORNERS. MODELS DISAGREE ON HOW QUICKLY THIS SYSTEM WILL MOVE EAST OF THE FORECAST AREA....WITH THE GFS PUSHING THE SYSTEM GENERALLY THROUGH BY TUESDAY EVENING. THE ECMWF HANGS THE MOISTURE BACK A BIT LONGER...THOUGH HAS MOST OF THE MOISTURE GONE BY THE EARLY MORNING HOURS OF WEDNESDAY. WITH A LONGER DURATION EVENT...SNOWY TRAVEL CONDITIONS WILL REMAIN A CONCERN FOR THOSE PLANNING HOLIDAY TRAVEL. KEEP TRACK OF CURRENT FORECASTS FOR UPDATES. && .AVIATION.../06Z ISSUANCE/ WEST OF THE DIVIDE...MVFR CLOUD DECKS WITH HIGHER MOUNTAIN OBSCURATIONS WILL BE WIDESPREAD THROUGH 14Z VCNTY AND WEST OF A 30S KLVM-KJAC-KAFO LINE. EXPECT GRADUAL EROSION/IMPROVEMENT 14Z-18Z WITH VFR CONDITIONS PREVAILING IN THE AFTERNOON AND EVENING. LCL IFR/LIFR CIGS AND VALLEY FOG WILL FORM 06Z-12Z FRIDAY PARTIALLY OBSCURING TERRAIN. EAST OF THE DIVIDE...SOUTHWEST FLOW WILL INCREASE THIS MORNING THROUGH THE WIND CORRIDOR FROM VCNTY 50NE KRKS-KCPR...SFC WINDS OF 25-40KTS EXPECTED FROM LATE MORNING THROUGH THE EARLY EVENING. OTHERWISE VFR CONDITIONS WILL PREVAIL WITH UNLIMITED CIGS. && .FIRE WEATHER... CONTINUED DRY AND COLD WITH ONLY A FEW MOUNTAIN FLURRIES. VALLEY AND BASIN INVERSIONS WILL DEVELOP TONIGHT AS A FLAT RIDGE OF HIGH PRESSURE MOVES IN. MOUNTAIN TOP TEMPERATURES WILL BEGIN TO MODERATE THIS EVENING AS WARMER AIR MOVES IN. STRONG SOUTHWEST WINDS WILL DEVELOP AGAIN ACROSS THE WIND CORRIDOR FROM JEFFREY CITY TO CASPER TONIGHT AND THURSDAY AND ALSO IN THE CODY FOOTHILLS. MAINLY DRY WEATHER IS EXPECTED TO CONTINUE INTO FRIDAY WITH GRADUALLY MODERATING TEMPERATURES. THE NEXT STORM SYSTEM WILL MOVE IN LATE IN THE WEEKEND INTO EARLY NEXT WEEK. && .RIW WATCHES/WARNINGS/ADVISORIES... HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST THURSDAY WYZ003. && SHORT TERM...ALLEN LONG TERM...BRANHAM AVIATION...AEM FIRE WEATHER...ALLEN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 310 PM MST WED DEC 19 2012 WYZ001>020-022>030-201311- 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- 310 PM MST WED DEC 19 2012 ...HIGH WIND WARNING FOR THE CODY FOOTHILLS TONIGHT AND THURSDAY MORNING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TONIGHT TONIGHT INTO THURSDAY MORNING...VERY STRONG WINDS IN THE CODY FOOTHILLS FROM CODY TO CLARK. WEST WINDS OF 30 TO 40 MPH WITH GUSTS OVER 60 MPH WILL BE POSSIBLE. EXPECT DIFFICULT TRAVEL FOR HIGH PROFILE VEHICLES AND LIGHT TRAILERS ALONG HIGHWAY 120 BETWEEN CODY AND CASPER OVERNIGHT. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH CHRISTMAS THURSDAY...STRONG WINDS WILL BE POSSIBLE ACROSS SOUTHEAST FREMONT COUNTY...AND MUCH OF NATRONA COUNTY. SUNDAY THROUGH CHRISTMAS DAY...HOLIDAY TRAVEL AND ACTIVITIES COULD BE IMPACTED AT TIMES BY LIGHT TO MODERATE SNOW. CURRENTLY...WESTERN WYOMING WILL HAVE THE BEST CHANCE FOR SNOW SUNDAY AND SUNDAY NIGHT...WHILE AREAS EAST OF THE DIVIDE COULD BE IMPACTED SUNDAY NIGHT INTO CHRISTMAS EVE DAY. SNOWFALL ACROSS THE EAST IS EXPECTED TO BE LIGHTER AND LESS WIDESPREAD...THAN WHAT OCCURS ACROSS WESTERN WYOMING. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY WINDS ABOVE 45 MPH OR ANY DAMAGE CAUSED BY STRONG WIND. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 1050 PM MST WED DEC 19 2012 WYZ019-020-201900- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS- 1050 PM MST WED DEC 19 2012 SOUTHWEST WINDS WILL INCREASE TO 25 TO 35 MPH WITH GUSTS OVER 50 MPH THROUGH THURSDAY MORNING. VERY WINDY CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE AFTERNOON. OPERATORS OF LIGHTWEIGHT AND HIGH PROFILE VEHICLES SHOULD BE ESPECIALLY CAUTIOUS OF STRONG CROSSWINDS ALONG HIGHWAYS 287...220...AND ALONG WYOMING BOULEVARD/OUTER DRIVE ON THE SOUTH AND EAST SIDES OF CASPER. AEM
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
The observation station 8 miles SSW of Clark recorded wind gusts of 60 and 62 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, December 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: 417208.