A strengthening pressure gradient ahead of a winter storm system brought high wind to areas east of the Continental Divide. High wind was recorded along the Green Mountains and Rattlesnake Hills north through Natrona and Johnson counties.
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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.
A strengthening pressure gradient ahead of a winter storm system brought high wind to areas east of the Continental Divide. High wind was recorded along the Green Mountains and Rattlesnake Hills north through Natrona and Johnson counties. A large McDonald's sign was blown down onto a roadway near the intersection of CY Avenue and Wyoming Boulevard in southwest Casper at 1057MST Thursday, December 29.
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 28, 2:36 AM MST, 8 hours 20 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 236 AM MST WED DEC 28 2011 .SHORT TERM...TODAY THROUGH FRIDAY NIGHT THE SURFACE PRESSURE GRADIENT CONTINUES TO TIGHTEN AS A LOW PRESSURE SYSTEM APPROACHES FROM THE PACIFIC AND HIGH PRESSURE CONTINUES TO HOLD OVER NORTHERN UTAH...PRODUCING AREAS OF STRONG WIND ALONG AND NEAR THE EAST SLOPES OF THE MOUNTAINS AND THROUGH THE WIND CORRIDOR THROUGH THURSDAY...GUSTY WINDS WILL CONTINUE IN SEVERAL OTHER AREAS...INCLUDING THE WIND RIVER BASIN. THE WINDS WILL KEEP THE AIR MIXED IN THE VALLEYS AND BASINS WITH TEMPERATURES REMAINING ABOVE NORMAL OVER MUCH OF THE STATE THROUGH THE WORK WEEK. SNOWFALL WILL INCREASE AND BECOME WIDESPREAD OVER THE WEST THROUGH THE DAY...CONTINUING INTO THURSDAY. THERE IS A HEALTHY PLUME OF PACIFIC MOISTURE ACCOMPANYING THE TROUGH WHICH SHOULD EASILY PILE UP TO WARNING SNOWFALL AMOUNTS IN THE WESTERN MOUNTAINS...EVEN THOUGH THE AIRMASS IS ON THE WARM SIDE. THERE IS SOME QUESTION AS TO WHETHER ENOUGH SNOW WILL MAKE IT AS FAR EAST AS SOUTH PASS...AT LEAST ENOUGH TO REQUIRE A WARNING. HAVE KEPT A WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW BECAUSE OF THE IMPACT THAT ANY SMALL AMOUNT OF SNOW WILL HAVE AT SOUTH PASS AS THERE WILL BE STRONG WINDS THROUGH THE PERIOD. ANOTHER AREA THAT COULD BE HIT HARD TONIGHT WOULD BE THE UPPER WIND RIVER BASIN INCLUDING DUBOIS. THERE COULD BE ENOUGH SNOW FALL BLOWING OVER THE MOUNTAINS TO PRODUCE SEVERAL INCHES OF SNOW...IN ADDITION TO SOME VERY STRONG WINDS...GUSTS COULD EXCEED 50 MPH AT TIMES TONIGHT INTO THURSDAY MORNING...WHICH WOULD CREATE DIFFICULT TRAVEL CONDITIONS AND LOW VISIBILITY IN BLOWING SNOW...SOME OF THESE WINDS COULD ALSO MAKE IT FURTHER INTO THE WIND RIVER BASIN AND BRING STRONG GUSTS INTO THE RIVERTON AREA EARLY THURSDAY MORNING. THESE AREAS WILL BE WATCHED FOR POSSIBLE HIGHLIGHTS. THE MODELS DIVERGE WITH THE EVOLUTION OF THE PRECIPITATION MAINLY THURSDAY AFTERNOON AND EVENING. THERE SHOULD BE A BREAK IN THE SNOWFALL...AT LEAST THE HEAVIEST SNOWFALL IN THIS TIME FRAME. SNOW THEN SHOULD PICK UP LATER THURSDAY NIGHT AND FRIDAY WITH A SECOND PROLONGED PERIOD OF SIGNIFICANT SNOWFALL EXPECTED THROUGH FRIDAY NIGHT. UP TO 2 FEET OF SNOW EXPECTED IN THE TETONS WITH THE FIRST BATCH AND ANOTHER FOOT OR MORE OF SNOWFALL WITH THE SECOND BATCH...SOME AREAS OF THE TETONS AND GROS VENTRE MOUNTAINS COULD EASILY SEE 3 FEET OF SNOW OR MORE. COLDER AIR MOVES IN BEHIND THE SYSTEM ON FRIDAY...WHICH SHOULD KNOCK FRIDAY NIGHT LOWS BACK TOWARD SEASONAL NORMS. .LONG TERM...SATURDAY THROUGH WEDNESDAY SATURDAY...AREAS OF SNOW IN THE WESTERN MOUNTAINS AND VALLEYS DIMINISHING THROUGH THE DAY. BREEZY TO WINDY AND COOLER. SUNDAY THROUGH WEDNESDAY...DRY...WINDS GENERALLY LIGHT...TEMPERATURES NEAR OR SLIGHTLY ABOVE NORMAL...COLDER IN SNOW-COVERED WESTERN VALLEYS. 00Z GLOBAL MODELS HAVE NOT STRAYED MUCH FROM AN OVERALL TRANSITION TO A MORE AMPLIFIED PATTERN OVER THE WEEKEND WITH GFS/ECMWF/GEM GENERALLY STICKING TO THEIR INDIVIDUAL BIASES. LAST IN A SERIES OF UPPER TROUGHS...THE STRONGEST OF THE BUNCH...BLASTS THROUGH THE AREA SATURDAY MORNING AND DIGS INTO THE PLAINS IN RESPONSE TO UPSTREAM RIDGE AMPLIFYING ALONG WEST COAST. ECMWF AND GEM CONTINUE TO SHOW MORE AMPLIFICATION...LESS PROGRESSION THAN GFS...THE FORMER RESULTING IN A COLDER NW FLOW THROUGH SUNDAY BRINGING H7 -20C ISOTHERM DOWN INTO NE WYOMING SUNDAY MORNING. GEFS MEAN A GOOD COMPROMISE BETWEEN THESE TWO SOLUTIONS. UPPER RIDGE AMPLIFIES OVER INTERMOUNTAIN WEST LATE SUNDAY FLANKED BY DEEP TROUGHS OVER THE EASTERN PACIFIC AND EASTERN U.S. PREFER ECMWF FOR SLOWER PROGRESSION OF LONGWAVE PATTERN BUT DISCOUNTED ITS RATHER STRONG SHORTWAVE MOVING THROUGH RIDGE ACROSS NORTHERN ROCKIES/NORTHERN HIGH PLAINS ON TUESDAY. THIS ENERGY MORE LIKELY TO DAMPEN OUT...AS IT MOVES THROUGH STRONG UPPER RIDGE. .AVIATION.../12Z ISSUANCE/ WEST OF THE DIVIDE...MOIST WESTERLY FLOW WILL RESULT IN WIDESPREAD MVFR/IFR CONDITIONS DEVELOPING THIS MORNING INTO EARLY AFTERNOON...AND LASTING THROUGH TONIGHT. LIGHT SNOW OVER NORTHWEST WYOMING THIS MORNING IS EXPECTED TO GRADUALLY EXPAND SOUTHWARD LATER TODAY. THE HEAVIEST SNOWFALL IS EXPECTED TONIGHT INTO THURSDAY MORNING. KJAC TERMINAL WILL BE THE HARDEST HIT ACROSS WESTERN WYOMING WITH PREVAILING LIFR IN SNOWFALL FOR MUCH OF TONIGHT. MOUNTAINS WILL BE OBSCURED...WITH LIFR CONDITIONS EXPECTED ACROSS MOUNTAIN PASSES THROUGH MUCH OF THE TAF FORECAST PERIOD. EAST OF THE DIVIDE AND SWEETWATER COUNTY...VERY WINDY WEST TO SOUTHWEST WINDS ARE EXPECTED OVER MUCH OF THE TYPICAL WINDY AREAS...SUCH AS BETWEEN KRKS-KCPR...AS WELL AS AROUND KCOD AND KU25. LOW LEVEL WIND SHEAR COULD ALSO BE PRESENT AT TIMES ACROSS THE FOOTHILLS LOCATED ON THE EAST SIDE OF THE MOUNTAIN RANGES. THIS WOULD AFFECT KCOD AND KLND TERMINALS...WITH KCOD SEEING MORE TURBULENT FLOW. OTHERWISE...VFR AND DRY CONDITIONS ARE EXPECTED...EXCEPT FOR AREAS ALONG THE DIVIDE WHERE SNOW AND LOW CEILINGS ARE EXPECTED. MVFR CEILINGS ARE LIKELY AT KU25 THIS AFTERNOON INTO TONIGHT. .FIRE WEATHER... A PACIFIC STORM SYSTEM WILL MOVE INLAND WITH THE LEADING EDGE OF SNOWFALL ALREADY MOVING INTO THE WESTERN MOUNTAINS OF WYOMING. THE SNOWFALL WILL INCREASE AND BECOME WIDESPREAD OVER THE WEST THROUGH THE DAY. THE EAST SLOPES OF THE MOUNTAINS AND WIND CORRIDOR SHOULD SEE HIGH WINDS DEVELOP. SNOWFALL AND WIND WILL CONTINUE WEDNESDAY NIGHT INTO THURSDAY. WINTER STORM WARNINGS AND HIGH WIND WARNINGS ARE IN EFFECT. PLEASE REFER TO THESE PRODUCTS FOR MORE SPECIFIC DETAIL ON THE DEVELOPING STORM. && .RIW WATCHES/WARNINGS/ADVISORIES... HIGH WIND WARNING FROM 5 AM EARLY THIS MORNING TO 8 AM MST THURSDAY WYZ019-020. WINTER STORM WARNING FROM 11 AM THIS MORNING TO 5 PM MST THURSDAY WYZ001-002-012>014-023>025. HIGH WIND WARNING UNTIL 8 AM MST THURSDAY WYZ003. WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 5 PM MST THURSDAY WYZ015. && SHORT TERM...ALLEN LONG TERM...AEM AVIATION...WM FIRE WEATHER...ALLEN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MST WED DEC 28 2011 WYZ001>020-022>030-291200- 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- 500 AM MST WED DEC 28 2011 ...HIGH WIND WARNING FOR CODY FOOTHILLS...SOUTHEAST FREMONT COUNTY AND MUCH OF NATRONA COUNTY THROUGH THURSDAY MORNING... ...WINTER STORM WILL AFFECT MUCH OF THE WEST THIS AFTERNOON THROUGH THURSDAY... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT STRONG WIND IS EXPECTED ACROSS THE CODY FOOTHILLS AND THROUGH THE CENTRAL WIND CORRIDOR...MAINLY FROM HIGHWAY 789 TO CASPER...PLEASE THE LATEST STATEMENTS ON THIS ONGOING HIGH WIND EVENT. A WINTER STORM WILL BEGIN TO AFFECT AREAS WEST OF THE DIVIDE TODAY. A PROLONGED PERIOD OF SNOWFALL...HEAVY AT TIMES WILL RESULT IN SIGNIFICANT SNOW ACCUMULATION. MOUNTAIN SNOWFALL OF ONE TO TWO FEET WILL BE COMMON THROUGH THURSDAY. SNOWFALL IN THE VALLEYS WILL VARY WIDELY BETWEEN 5 AND 15 INCHES DEPENDING UPON LOCATION. TRAVEL OVER MOUNTAIN PASSES AND THROUGH VALLEYS OF THE WEST WILL BE HAMPERED DUE TO THE SNOW AND GUSTY WIND. FOR THE LATEST INFORMATION PLEASE GO TO WWW.WEATHER.GOV/RIVERTON. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY THURSDAY...HEAVY SNOW IN THE WEST AND AREAS OF STRONG WIND CONTINUE THURSDAY MORNING...DIMINISHING THURSDAY AFTERNOON. THURSDAY NIGHT AND FRIDAY...SNOW INCREASES AGAIN ACROSS THE WEST THURSDAY NIGHT WITH ANOTHER ROUND OF SIGNIFICANT SNOWFALL EXPECTED THROUGH FRIDAY NIGHT. STRONG WINDS LIKELY TO DEVELOP OVER PORTIONS OF CENTRAL WYOMING FRIDAY AFTERNOON AND NIGHT. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT WINDS OVER 45 MPH...AND ANY DAMAGE ASSOCIATED WITH THE STRONG WINDS. WESTERN SPOTTERS ARE REQUESTED TO PROVIDE SNOWFALL TOTALS WEDNESDAY AND THURSDAY. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
5 high wind. Local standard time, as filed.
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, December 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: 357362, 357361, 357363, 357360, 357364.