Strong west to northwest mid-level winds spread across Wyoming and mainly impacted northern and central sections of the state on Wednesday, December 9. A tight surface pressure gradient ahead of an approaching cold front and strong winds mixing to the surface behind the cold front also resulted in high wind.
Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
Strong west to northwest mid-level winds spread across Wyoming and mainly impacted northern and central sections of the state on Wednesday, December 9. A tight surface pressure gradient ahead of an approaching cold front and strong winds mixing to the surface behind the cold front also resulted in high wind. The strongest winds were in the favored areas of the Absaroka Range and in the lee of that range. Hurricane force wind gusts were recorded at all the wind sensors near Clark, including a maximum of 103 mph during the morning of December 9. A sensor on nearby Chief Joseph Pass registered a gust of 96 mph around the same time. Strong winds also occurred in portions of central Wyoming. Some of the strongest wind gusts were 70 mph on the south side of Casper, 68 mph at Lander, and a 64 mph gust at Riverton Regional Airport. Strong wind south of Lander blew over one semitrailer and pushed another off State Highway 789 around 1630MST. Both vehicles were empty.
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 8, 2:43 PM MST, 6 hours 7 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 243 PM MST TUE DEC 8 2015 .SHORT TERM...TONIGHT THROUGH WEDNESDAY VERY WINDY THROUGH THE SHORT TERM AS ANOTHER SHORT WAVE APPROACHES FOR WEDNESDAY. MOUNTAIN WAVE ACTIVITY ACROSS THE ABSAROKAS WILL BREAK TO THE SURFACE AGAIN TONIGHT...LEADING TO SOME SIGNIFICANT WIND GUSTS AND STRONG DOWNSLOPE WARMING ALONG THE CODY FOOTHILLS. A 145 KNOT JET NOSES IN ON WEDNESDAY...SUPPLYING SOME DOWNWARD FORCING AND SPREADING STRONG WIND A LITTLE DEEPER INTO THE FOOTHILLS AND ALONG THE SOUTHERN WIND CORRIDOR. 700MB FLOW EAST OF THE DIVIDE IS BETWEEN 50 AND 70KT BY WEDNESDAY AFTERNOON. HIGH PRESSURE BUILDING IN FROM THE SOUTHWEST WILL PUSH THE STRONGER SURFACE GRADIENT A LITTLE FURTHER NORTH AND EAST...SO LEFT SWEETWATER COUNTY OUT OF THE WATCH BUT ADDED NATRONA COUNTY FOR WEDNESDAY MORNING THROUGH EARLY THURSDAY MORNING. AS THE SHORT WAVE ARRIVES IN THE WEST...EXPECT RAIN AND SNOW TO INCREASE IN INTENSITY AND COVERAGE WEDNESDAY AFTERNOON. IT WILL BE QUITE WARM AHEAD OF THE WAVE SO EXPECT SNOW LEVELS TO BE FAIRLY HIGH FOR THIS TIME OF YEAR...AROUND 7000 FT. .LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY VERY ACTIVE PERIOD WITH BOTH WIND AND SNOW TO CONTEND WITH. STRONG SHORTWAVE IS BLASTING ACROSS THE NORTH HALF WEDNESDAY EVENING WITH DECENT FROPA ACROSS THE AREA. FAIRLY STRONG PRESSURE GRADIENT AND VERY STRONG MID LEVEL WINDS OF 55-65KTS COMBINED WITH 150KT+ JET WILL AID IN HIGH WINDS ACROSS WIND CORRIDOR...DUBOIS TO RIVERTON CORRIDOR POSSIBLY AND CONTINUING IN THE CODY FOOTHILLS/NEARBY EAST SLOPE MTNS. SEVERAL MTN WAVE EPISODES EXPECTED IN THE CODY FOOTHILLS BEGINNING IN THE SHORTER TERM WITH THE LAST ONE EXPECTED LATER WED NGT. THE HIGH WIND WATCH FOR THE WIND CORRIDOR LOOKS SOLID WELL INTO THE EVENING BEFORE SOME DECREASE LATE...ESPECIALLY ERN SECTIONS. THE DUBOIS TO RIVERTON CORRIDOR MAY SEE HIGH WINDS WEDNESDAY NIGHT AS FRONT BLASTS THROUGH WITH STRONG PRESSURE RISES...WINDS SHIFTING TO THE NW AND POTENTIAL UPPER JET SUPPORT. WINDY FOR SURE AND POSSIBLY HIGH WIND. OUT WEST...SNOW WILL CONTINUE INTO THE EVENING BEFORE WE GET A BRIEF RESPITE FROM OUR NEXT...STRONGER SYSTEM THURSDAY INTO THURSDAY NIGHT. PATTERN IS TRANSITIONING INTO A LONGWAVE TROUGH OVER THE WEST AND THE PACIFIC IS RATHER BUSY RIGHT NOW WITH A LARGE NUMBER OF STORM SYSTEMS. THE THURSDAY ONE LOOKS TO ORIGINATE OUT NEAR 40N/170W AND WILL RACE QUICKLY EWD. THIS SYSTEM WILL START OUT WITH SOME DECENT UPGLIDE BY THURSDAY MORNING AND THEN INCREASE WEDNESDAY AFTERNOON INTO WEDNESDAY AFTERNOON WITH APPROACHING SHORTWAVE AND NEXT FRONTAL SYSTEM. NOSE OF CYCLONICALLY CURVED JET MOVES INTO NRN UT/SWRN WYO WITH UPPER JET DIVERGENCE FORECAST OVER THE WEST THURSDAY AFTN AND EVE. COMBINATION OF SNOWFALL AND WIND (ESPECIALLY FIRST HALF OF THE EVENT) COULD MAKE THIS A WINTER STORM FOR PARTS OF THE WEST. LOWERED TEMPS IN THE VALLEYS AS AMOUNT OF COLD AIR BEHIND THE WED SYSTEM FOLLOWED QUICKLY BY DEVELOPING PCPN SHOULD PRODUCE MOSTLY SNOW OUT WEST ON THURSDAY. THERE IS WARMING THURSDAY AFTERNOON BUT TEMPS ARE STILL HOLDING GENERALLY -4 TO -5C IN THE STAR VALLEY AND COLDER NORTH. THE FAR SRN ZONES COULD BE A BRIEF MIXTURE. HIT THE POPS HARDER AND SNOWFALL ON THE HIGH END OF THE ADVISORY TO LOW END OF THE WARNING CRITERIA THU AND THUR NGHT. NOT AS MUCH AS THE WINTER WEATHER DESK BUT TRENDING UP. MORE WIND FOR THE WIND CORRIDOR DURING THIS SYSTEM WITH POTENTIAL FOR HIGH WINDS AGAIN IF RAPIDLY DEVELOPING SURFACE LOW INDICATED DEVELOPS OVER THE NRN ZONES AND THEN SHIFTS INTO NERN WYO LATE THUR. SOME SIGNIFICANT DISAGREEMENT ON HOW MUCH OF THIS MAY GET EAST OF THE DIVIDE. THE BEST CHANCE WILL LIKELY BE THE I80 CORRIDOR THURSDAY NIGHT AND POSSIBLY AS FAR UP AS CASPER/CPR MTN. COULD SEE A QUICK SWATH OF AN INCH OR TWO WITH STRONG WIND FOR A FEW HOURS AS THE FRONT MOVES EAST...ESPECIALLY SRN ZONES. COLD AND UNSETTLED BEHIND THIS SYSTEM OVER THE WEEKEND WITH A CHANCE OF LIGHT SNOW FOR MAINLY THE MOUNTAINS. BY LATER SUNDAY AND ESPECIALLY INTO EARLY NEXT WEEK THERE ARE LARGE DIFFERENCES BETWEEN THE ECMWF/GEM SOLUTIONS AND THE GFS. THE ECMWF/GEM SHOW A DECENT POTENTIAL FOR A MAJOR WINTER STORM IN CENTRAL WYOMING MONDAY INTO PART OF TUESDAY. THE GFS SHOWS THIS SYSTEM SPLITTING MORE WITH A SIGNIFICANT CHUNK OF THE ENERGY GOING NORTH AND SOME GOING SOUTH. CONSIDERING THE BIGGER PICTURE HAS A LONG WAVE TROUGH OVER THE WEST...I'D LEAN TOWARDS A MORE CONSOLIDATED UPPER SYSTEM BUT EXACT LOCATION IS STILL UP FOR DEBATE. THE ECMWF/GEM ARE PRETTY SIMILAR RIGHT NOW BUT WE NEED JUST A LITTLE BIT MORE CONSISTENCY AND A FEW MORE RUNS BEFORE WE START TO HIT IT ANY HARDER. DID BRING IN SOME CHANCE POPS BEST I COULD MONDAY BUT LATER SHIFTS CAN ADJUST THIS AS CONFIDENCE GROWS (OR DOESN'T). EITHER WAY...SHOULD BE AN ACTIVE PERIOD FOR THROUGH THE MEDIUM RANGE PERIOD AND BEYOND. THE EXTENDED GFS...BEYOND 240 HOURS...SHOWS THE ACTIVE PERIOD CONTINUING FOR AT LEAST ANOTHER WEEK BEYOND THIS PERIOD. && .AVIATION.../00Z ISSUANCE/ WEST OF THE CONTINENTAL DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES FAST WESTERLY FLOW CONTINUES TO STREAM MOISTURE INTO THE WESTERN MOUNTAINS. ISOLATED TO WIDELY SCATTERED SNOW SHOWERS OBSCURING THE MOUNTAINS WITH OCCASIONAL -SHRASN IN THE VALLEYS. AREAS OF LOW VFR TO OCCASIONAL MVFR CIGS WILL REMAIN ACROSS THE FAR WEST VALLEYS VCNTY KJAC- KAFO. AREAS OF LOWER IFR/MVFR STRATUS POSSIBLY DEVELOPING OVER THE VALLEYS... VCNTY KJAC- KBPI- KPNA TONIGHT WITH BCFG INTRODUCED INTO THE TAFS AT BPI AND PNA WITH LOW CIGS...CONDITIONS MAY END UP BEING WORSE THAN FORECAST BUT WENT CONSERVATIVE AT THIS TIME...WITH LOW VSBY AND CIGS MOST LIKELY BETWEEN MIDNIGHT AND 17Z WED. A RICHER PUSH OF MOISTURE ARRIVES TOWARD THE END OF THE TAF PERIOD TOMORROW WITH MVFR CIGS AND -SNRA BELOW 7KFT TURNING TO SNOW BEHIND A COLD FRONT...EXPECTED TO SWING THROUGH AFTER 00Z. WINDS WILL BE VERY GUSTY...ESPECIALLY IN THE MOUNTAINS WITH ELEVATED AND BREAKING MOUNTAIN WAVES ALONG AND JUST EAST OF THE ABSAROKAS...WIND RIVER RANGE...AND BIGHORNS WITH MOD-SVR TURBULENCE EXPECTED. VISIT AVIATIONWEATHER.GOV FOR MORE INFORMATION ON ICING AND TURBULENCE...INCLUDING MOUNTAIN WAVE TURBULENCE. EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KLND/KRIW/KRIW ROUTES W-SW WINDS AT 20-30KTS WILL PREVAIL VCNTY KRKS TO KCPR THROUGH THIS EVENING. STRONG WINDS AND A BREAKING MOUNTAIN WAVE RETURN TO THE CODY FOOTHILLS THIS EVENING...AFFECTING KCOD AND TO A LESSER EXTENT KPOY THROUGH THE TAF PERIOD WITH ERRATIC EDDYS AND OCCASIONALLY STRONG WESTERLY GUSTS. LLWS WILL BE POSSIBLE AS WELL. AN ELEVATED MOUNTAIN WAVE OVER THE WIND RIVERS COULD AFFECT THE WIND RIVER BASIN...INCLUDING KLND AND TO A LESSER EXTENT KRIW...HAVE LLWS MENTIONED IN THE KLND TAF WITH SOME GUSTS MAKING IT TO THE SURFACE...BUT FUNNELING WILL CHANGE THE WIND DIRECTION A BIT...SO THERE COULD BE SIGNIFICANT SPEED AND DIRECTIONAL LLWS AT KLND OVERNIGHT INTO WEDNESDAY MORNING. WINDS WILL ALSO BE ON THE UPTICK AROUND KCPR ON WEDNESDAY MORNING...WITH WIND GUSTS OVER 45KT EXPECTED THROUGH WEDNESDAY NIGHT. VISIT AVIATIONWEATHER.GOV FOR MORE INFORMATION ON ICING AND TURBULENCE...INCLUDING MOUNTAIN WAVE TURBULENCE. && FIRE WEATHER... WIND ACROSS THE AREA WILL REMAIN A CONCERN FOR THE NEXT COUPLE OF DAYS. A TIGHTENING PRESSURE GRADIENT ON WEDNESDAY WILL PERMIT STRONGER WINDS TO DEVELOP ACROSS THE WIND CORRIDOR BETWEEN ROCK SPRINGS AND CASPER...ALONG THE CODY FOOTHILLS...AND IN THE MOUNTAINS...MIGRATING INTO THE WIND RIVER BASIN EARLY ON THURSDAY. HUMIDITIES ARE EXPECTED TO REMAIN HIGH...BUT THE WIND ACTIVITY MAY ENHANCE FIRE BEHAVIOR CONCERNS. OUTSIDE OF WIND....PERIODS OF SNOWFALL WILL BE POSSIBLE...MAINLY ACROSS TETON DISPATCH FOR THE NEXT COUPLE OF DAYS. && .RIW WATCHES/WARNINGS/ADVISORIES... HIGH WIND WARNING FROM 7 PM THIS EVENING TO 5 AM MST THURSDAY FOR WYZ002-003. HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT FOR WYZ019-020. HIGH WIND WATCH FROM WEDNESDAY EVENING THROUGH LATE WEDNESDAY NIGHT FOR WYZ016-017. && SHORT TERM...ALLEN LONG TERM...SKRBAC AVIATION...ALLEN FIRE WEATHER...ALLEN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 310 PM MST TUE DEC 8 2015 WYZ001>020-022>030-091300- YELLOWSTONE NATIONAL PARK-ABSAROKA MOUNTAINS-CODY FOOTHILLS- NORTH BIG HORN BASIN-SOUTHWEST BIG HORN BASIN- SOUTHEAST BIG HORN BASIN-OWL CREEK AND BRIDGER MOUNTAINS- BIGHORN MOUNTAINS WEST-BIGHORN MOUNTAINS SOUTHEAST- NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY- TETON AND GROS VENTRE MOUNTAINS-JACKSON HOLE- WIND RIVER MOUNTAINS WEST-WIND RIVER MOUNTAINS EAST- UPPER WIND RIVER BASIN-WIND RIVER BASIN-LANDER FOOTHILLS- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS-CASPER MOUNTAIN-STAR VALLEY- SALT RIVER AND WYOMING RANGES-UPPER GREEN RIVER BASIN FOOTHILLS- UPPER GREEN RIVER BASIN-SOUTH LINCOLN COUNTY- ROCK SPRINGS AND GREEN RIVER-FLAMING GORGE-EAST SWEETWATER COUNTY- 310 PM MST TUE DEC 8 2015 ....HIGH WIND WARNINGS CONTINUE FOR THE CODY FOOTHILLS AND NEARBY ABSAROKA MOUNTAINS TONIGHT THROUGH WEDNESDAY NIGHT... ...HIGH WIND WATCHES COVER THE WIND CORRIDOR FROM JEFFREY CITY TO CASPER WEDNESDAY AND WEDNESDAY NIGHT... ...HIGH WIND WATCH FROM DUBOIS TO RIVERTON WEDNESDAY NIGHT... THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT STRONG WIND MAY BE PRESENT TONIGHT ACROSS THE CODY FOOTHILLS. WIND GUSTS IN EXCESS OF 60 MPH CAN BE EXPECTED WITH EVEN STRONGER WINDS AROUND CLARK AND SOUTH OF CODY. THESE STRONGER WINDS WOULD AGAIN IMPACT HIGHWAY 120 NORTH OF CODY AND JUST SOUTH OF CODY...ESPECIALLY FOR ANY LIGHTWEIGHT OR HIGH PROFILE VEHICLES. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WEDNESDAY....A TIGHTENING PRESSURE GRADIENT MAY BRING STRONG WIND ACROSS SOUTHEASTERN FREMONT COUNTY AND THROUGH NATRONA COUNTY. WIND GUSTS OF 55 TO 65 MPH ARE POSSIBLE. THESE WINDS WOULD IMPACT MOTORISTS IN HIGH PROFILE OR LIGHTWEIGHT VEHICLES. THESE HIGH WINDS MAY THEN IMPACT THE DUBOIS TO RIVERTON AREA WEDNESDAY NIGHT. THURSDAY...A SIGNIFICANT WINTER STORM MAY IMPACT PARTS OF THE FAR WEST THURSDAY AND THURSDAY NIGHT WITH SNOW AND WIND. MORE STRONG WIND IS POSSIBLE EAST OF THE DIVIDE. MONDAY...A NEW WINTER STORM COULD DEVELOP ACROSS THE AREA BUT CONFIDENCE IS LOW AT THIS TIME WITH LARGE DIFFERENCES IN COMPUTER MODEL SOLUTIONS. STAY TUNED FOR FURTHER UPDATES OVER THE COMING DAYS. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY WIND GUSTS GREATER THAN 50 MPH. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
6 high wind. Local standard time, as filed.
Numerous sites across the Green Mountains and Rattlesnake Range recorded wind gusts over 58 mph. Some of these included 68 mph at Camp Creek, 67 mph at Beaver Rim, and 66 mph at Fales Rock.
The wind sensor along the Chief Joseph Highway recorded sustained winds of 60 mph with many gusts of hurricane force. The maximum wind gust was 96 mph.
The wind sensor along Outer Drive south of Casper recorded several wind gusts over 58 mph including a maximum of 70 mph.
Hurricane force wind gusts occurred at all three wind sensors in the vicinity of Clark. The strongest gusts were 103 mph 5 miles WNW of Clark, 80 mph 8 miles SSW of Clark, and 74 mph at Clark.
The ASOS at the Lander Airport reported wind gusts of 68 and 58 mph.
The ASOS at Riverton Regional Airport reported a wind gust of 64 mph following a cold frontal passage. A 59 mph gust was recorded northwest of Hudson.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2015Every state in 2015This day in weather historyWarnings in Wyoming, December 2015
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: 607108, 607106, 607109, 607107, 607112, 607110.