A combination of very cold air over the Yellowstone Plateau and an increasing pressure gradient associated with a southeast-moving Alberta Clipper produced strong winds in localized sections of Park, Natrona, and Fremont counties. Strong gradient wind over 70 mph was measured in extreme southeast Fremont County and in Natrona County.
Every event with a place to put it; 3 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.
A combination of very cold air over the Yellowstone Plateau and an increasing pressure gradient associated with a southeast-moving Alberta Clipper produced strong winds in localized sections of Park, Natrona, and Fremont counties. Strong gradient wind over 70 mph was measured in extreme southeast Fremont County and in Natrona County. The Camp Creek RAWS recorded a peak gust of 72 mph before sunrise on December 17, while a mesonet sensor registered a peak gust of 71 mph along Outer Drive in south Casper shortly after 0500MST the same day. Occasional strong gap winds near Clark produced a peak wind gust of 63 mph.
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 17, 4:21 PM MST, 4 hours 29 minutes earlier.
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
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 332 PM MST THU DEC 17 2015 WYZ001>020-022>030-181300- 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- 332 PM MST THU DEC 17 2015 ...WINTER WEATHER ADVISORY FOR BLOWING SNOW AT THE LOWER ELEVATIONS OF NATRONA COUNTY TONIGHT AND FRIDAY MORNING... ...HIGH WIND WARNING FOR THE CODY FOOTHILLS TONIGHT... THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WY...CENTRAL WYOMING...NORTH CENTRAL WYOMING...NORTHWEST WYOMING...SOUTH CENTRAL WYOMING...SOUTHWEST WYOMING AND WEST CENTRAL WYOMING. .DAY ONE...REST OF THIS AFTERNOON AND TONIGHT TONIGHT...STRONG GAP FLOW THROUGH THE ABSAROKAS WILL LEAD TO WIND GUSTS IN EXCESS OF 60 MPH NEAR THE CANYONS. THIS COULD AFFECT LIGHT TRAILERS AND HIGH PROFILE VEHICLES ATTEMPTING TO TRAVEL ALONG HIGHWAY 120 BETWEEN CODY AND THE MONTANA BORDER. THE COMBINATION OF STRONG WINDS...DEEP FRESH SNOW COVER AND SUBFREEZING TEMPERATURES WILL RESULT IN CONSIDERABLE BLOWING AND DRIFTING SNOW WITH LOWERED VISIBILITY THROUGHOUT THE LOWER ELEVATIONS OF NATRONA COUNTY INCLUDING THE CITY OF CASPER TONIGHT. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY FRIDAY...WINDY FROM ROCK SPRINGS TO CASPER WITH AREAS OF BLOWING SNOW...ESPECIALLY AT THE LOWER ELEVATIONS OF NATRONA COUNTY IN THE MORNING WHERE DEEPER SNOW COVER EXISTS. FRIDAY NIGHT AND SATURDAY SATURDAY NIGHT...STRONG WINDS WITH GUSTS NEAR 60 MPH POSSIBLE ALONG THE CODY FOOTHILLS AND IN THE CASPER AREA. LIGHT SNOW THE WESTERN MOUNTAINS AND FAR WEST VALLEYS SATURDAY AFTERNOON AND EVENING. SUNDAY NIGHT AND MONDAY...LIGHT TO MODERATE SNOW ACROSS THE WEST. WINDY IN THE MOUNTAINS...FOOTHILLS AND EAST OF THE DIVIDE. MONDAY NIGHT AND TUESDAY...STRONG WINDS WITH GUSTS OVER 60 MPH POSSIBLE ACROSS MUCH OF CENTRAL AND SOUTHERN WYOMING. SNOW...BLOWING AND DRIFTING SNOW WITH VERY STRONG RIDGE TOP WINDS ACROSS THE WESTERN MOUNTAINS AND FAR WEST VALLEYS. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY SNOWFALL AMOUNTS OR WIND GUSTS IN EXCESS OF 50 MPH. THANK YOU.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 350 PM MST THU DEC 17 2015 WYZ022-181000- CASPER MOUNTAIN- 350 PM MST THU DEC 17 2015 THE COMBINATION OF FRESH DEEP SNOW COVER AND INCREASING SOUTHWEST WINDS OF 25 TO 35 MPH WILL RESULT IN CONSIDERABLE BLOWING AND DRIFTING SNOW TONIGHT AND FRIDAY...ESPECIALLY IN EXPOSED AREAS. SNOW DRIFTS OF SEVERAL FEET DEEP ARE EXPECTED. AREA ROADS WILL BECOME SLICK AS DRIFTING OCCURS...INCLUDING CASPER MOUNTAIN ROAD. THE VISIBILITY WILL LOWER TO ONE QUARTER OF A MILE OR LESS AT TIMES IN BLOWING SNOW. WYZ019-181000- GREEN MOUNTAINS AND RATTLESNAKE RANGE- INCLUDING THE CITY OF...JEFFREY CITY 350 PM MST THU DEC 17 2015 THE COMBINATION OF FRESH SNOW COVER AND INCREASING SOUTHWEST WINDS OF 30 TO 40 MPH WITH GUSTS TO 50 MPH WILL RESULT IN CONSIDERABLE BLOWING AND DRIFTING SNOW TONIGHT AND FRIDAY...ESPECIALLY IN EXPOSED AREAS. BEAVER RIM WILL BE ESPECIALLY SUSCEPTABLE TO THESE HAZARDS WHERE DEEPER SNOW COVER EXISTS ALONG WITH THE ADDED EXPOSURE. AREA ROADS WILL BECOME SLICK AS DRIFTING OCCURS. THE VISIBILITY WILL LOWER TO ONE QUARTER OF A MILE OR LESS AT TIMES IN BLOWING SNOW. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
3 high wind. Local standard time, as filed.
High winds blew across favored areas of the Green and Rattlesnake Range. The strongest wind gusts were 72 mph at Camp Creek and 69 mph at Fales Rock.
The wind sensor 5 miles WNW of Clark recorded wind gusts of 63 mph and 59 mph.
There were numerous wind gusts past 60 mph along Outer Drive in Casper including a maximum of 71 mph shortly after 0500MST.
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: 607270, 607269, 607271.