A strong feed of moisture from the Pacific Ocean combined with favorable upper-level dynamics and low-level upslope flow to produce heavy snow across portions of western and central Wyoming. The heaviest snow fell in Natrona County with Casper Mountain receiving the most snow with as much of 32 inches reported.
Every event with a place to put it; 10 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 strong feed of moisture from the Pacific Ocean combined with favorable upper-level dynamics and low-level upslope flow to produce heavy snow across portions of western and central Wyoming. The heaviest snow fell in Natrona County with Casper Mountain receiving the most snow with as much of 32 inches reported. The city of Casper had 10 to 16 inches with higher amounts in the southern sections of town. Thermopolis and Lander also had favorable upslope flow and averaged around 10 and 8 inches of new snow, respectively. Less snow fell in other areas, but gusty winds combined with the snow to produce near white-out conditions that closed major roads including Interstate 25 and US 20/26. Across the west, the most snow fell in the vicinity of Jackson Hole with reports of 6 to 12 inches fairly common, especially north of the town of Jackson.
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 13, 3:10 PM MST, 2 hours 50 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 310 PM MST SUN DEC 13 2015 .SHORT TERM...TONIGHT THROUGH MONDAY VARIOUS ADVISORIES AND WATCHES NOW OUT FOR THE ENTIRE FORECAST AREA. IMAGERY SHOWS PAC MOISTURE NOW MAKING ITS WAY INTO THE WRN FA...WITH SOUTHWEST FLOW AND MODEST DIVERGENCE ALOFT AHEAD OF A STRONG DIGGING TROF BUILDING DOWN THE WCST. THIS WILL BE THE PRIMARY PLAYER OVER THE NEXT COUPLE OF DAYS WITH ALL THAT IT BRINGS. THE SFC HAS LEE TROF ACROSS NERN WY...HIGH PRESSURE OVR THE SW HELP TO TIGHTEN THE P GRAD AND GIVE THE AREA BREEZY TO WINDY CONDITIONS ACROSS THE WIND CORRIDOR. SFC CYCLOGENESIS FORMING NEAR THE JUNCTION OF NV/OR/ID ATTM...JUST AHEAD AND WITH GOOD TILT BACK TO THE UPR DIGGING LOW P TROF. NNE/SSW COLD FRONT CURRENTLY FOLLOWS THIS LOW. THE REST OF TODAY AND TONIGHT OUT WEST...BREEZY TO WINDY CONDITIONS ACROSS THE WIND CORRIDOR BY THIS AFTERNOON. MAINLY TERRAIN FORCED PRECIPITATION...WITH SOME MODEST ADDITIONAL HELP FROM FORCING ALOFT...WILL SLOWLY INCREASE THRU THE DAY TODAY OUT WEST...EVENTUALLY BUILDING SWD FROM THE TETON RANGE. WHILE THE PRECIP WILL BEGIN AS SNOW...THERE MAY BE A SHORT PERIOD IN THE WESTERN VALLEYS DURING THE LATE AFTERNOON/EARLY EVENING PERIOD WHEN SNOW MAY MIX WITH RAIN FOR AN HOUR OR SO. ADVISORY AMOUNTS OF SNOW SHOULD BE ATTAINABLE OUT WEST WITH THIS SYSTEM...COVERING THE USUAL MOUNTAIN/VALLEY SUSPECTS OUT THAT WAY INCLUDING ZONES 1 2 12 13 14 23 24 AND 25. GREATEST STORM TOTAL AMOUNTS THRU MONDAY EVENING WILL RANGE FROM 8 TO 12 INCHES IN THE TETON RANGE...WITH LOCALIZED AREAS TO 14 INCHES...AND 5 TO 10 INCHES OVER THE OTHER MOUNTAIN GROUPS. THE VALLEYS WILL GENERALLY WITH SEE 3 TO 6 INCHES. TONIGHT AND TUESDAY DEVELOPING SFC CYCLONE WILL CONTINUE TO DEVELOP TOWARD NW WY/SRN MT AS STRONGER CYCLOGENESIS PROCEEDS ACROSS THE FRONT RANGE OF COLORADO THROUGH THE DAY MONDAY. AS THIS OCCURS...THE WEAKER CYCLONE OVR SRN MT WILL DISSOLVE...LEAVING THE ASSOCIATED STRONG COLD FRONT TO BE EFFECTIVELY YANKED SOUTHWARD ACROSS THE FA MONDAY AFTERNOON WITH DEEP NORTH TO NORTHEAST FLOW FOLLOWING MONDAY NIGHT THROUGH TUESDAY MORNING BEFORE BECOMING MORE NORTH TO NORTHWEST TUESDAY AFTERNOON/NIGHT. AREAS FAVORABLE FOR MODERATE TO HEAVY SNOW WILL BE ALONG/NEAR THE FRONT ITSELF AND ALSO OVR AREAS WHERE UPSLOPE FLOW MAXIMIZES PRECIP POTENTIAL...SUCH AS...EARLY ALONG THE CODY FOOTHILLS...THEN THE THE OWL/BRIDGER MOUNTAINS AND ADJACENT LOWER ELEVATIONS TO THE NORTH ...FOLLOWED BY THE WIND RIVER BASIN/LANDER AND OTHER FOOTHILLS OF THE WIND RIVER RANGE. GUSTY NORTH WINDS 20 TO 30 MPH ACCOMPANYING THE FRONTAL PASSAGE WILL COMBINE WITH MODERATE TO OCCASIONAL HEAVY SNOW TO SEVERELY REDUCE VISIBILITY AT TIMES IN THESE AREAS. WINTER WEATHER ADVISORIES AND WINTER STORM WATCHES START MONDAY AFTERNOON EAST OF THE DIVIDE AND ACROSS THE SOUTHERN FA...AND COVER THE ENTIRE FA THROUGH MOST OF THE DAY TUESDAY...WITH THE EASTERN COUNTIES REMAINING UNDER THESE HIGHLIGHTS THROUGH TUESDAY NIGHT. .LONG TERM...MONDAY NIGHT THROUGH SUNDAY WIDESPREAD SNOWFALL AND STRONG NORTHEAST WINDS LOOK FAVORABLE AS MODELS NOW HAVE THE STACKED LOW CUTTING OFF BETWEEN VERNAL AND FLAMING GORGE EARLY EVENING. LOW SHOULD THEN TRACK ALONG AND JUST SOUTH OF THE COLORADO BORDER AND SLOWLY JUMP THE ROCKIES INTO NORTHEAST COLORADO TUESDAY. THIS PUTS THE FAVORED UPSLOPE AREAS ALONG THE WIND RIVER AND ABSAROKA MOUNTAINS INTO A BETTER WIND DIRECTION FOR A LONGER PERIOD BEFORE THE NORTHEAST WINDS EVENTUALLY SHIFT AROUND TO THE NORTH AND EVENTUALLY NORTHWEST WHEN THE CUT OFF LOW EJECTS TO THE EAST. TEMPERATURES AND MOISTURE WILL BE FAVORABLE FOR MODERATE TO HEAVY SNOW AND OVER THE OPEN AREAS NORTHEAST WINDS GUSTING TO 35 TO 45 MPH WILL BE POSSIBLE IN THE BIGHORN BASIN... EASTERN JOHNSON COUNTY...NATRONA COUNTY SOUTHERN AND EASTERN FREMONT COUNTY AND EASTERN SWEETWATER COUNTY. IF THE WINDS HOOK UP WITH THE PERIODS OF HEAVIEST SNOWFALL...NEAR BLIZZARD CONDITIONS WOULD RESULT. EXPECT I 25 AND I 80 BOTH TO GET HAMMERED MONDAY NIGHT AND TUESDAY...TAPERING OFF IN THE AFTERNOON. AREAS OF 4 TO 10 INCHES EXPECTED WITH MOUNTAIN AREAS 10 TO 18 INCHES IN THE BIGHORN... ABSAROKA AND WIND RIVER MOUNTAINS AND ON CASPER MOUNTAIN. TUESDAY MORNING THE STACKED CUT OFF LOW WILL BE IN NORTHEAST TO EAST CENTRAL COLORADO WITH A BROAD ENOUGH CIRCULATION TO KEEP SURFACE TO MID LEVEL FLOW OUT OF THE NORTHEAST. THIS WILL END BY LATE AFTERNOON AS THE LOW EJECTS RAPIDLY INTO NORTH CENTRAL KANSAS AND NORTHWEST WINDS SET UP ACROSS WYOMING. LINGERING BANDS OF SNOW TO THE LEE OF THE MOUNTAINS WITH FAVORABLE CSI CONDITIONS WILL SUPPORT SOME LINGERING SNOW BUT THROUGH TUESDAY NIGHT THE AIR MASS WILL LOSE ITS MOISTURE AND STABLE COLD AIR WILL MOVE IN. REFER TO WINTER STORM WATCH FOR DETAILS OF THE STORM. A CANADIAN COLD FRONT WILL BRING A PERIOD OF SNOW MAINLY TO THE NORTH AND WEST WEDNESDAY. THIS WILL BRING IN COLDER AIR AND SNOW ACCUMULATIONS SHOULD BE LIGHT WITH LOW DENSITY FLUFFY SNOW. THIS SHOT OF SNOW WILL SWEEP THROUGH THE AREA BY MID DAY ON THURSDAY AS A STRONGER PACIFIC LOW PRESSURE TROUGH APPROACHES THE WEST COAST KICKING THE CANADIAN COLD FRONT TO THE EAST WITH A PERIOD OF DRY AND COLD AIR MOVING IN WITH PARTIAL CLEARING. TOO EARLY TO IDENTIFY AREAS OF POTENTIAL FOG AT THIS TIME. THURSDAY NIGHT THE LEADING EDGE OF THE PACIFIC MOISTURE WILL BRING SOME LIGHT SNOW TO THE WESTERN MOUNTAINS. STRONGER WEST WINDS WILL DEVELOP ACROSS THE SOUTH IN SWEETWATER AND SOUTHERN FREMONT COUNTIES..EVENTUALLY SPREADING INTO NATRONA CASPER. AS THE PACIFIC LOW PRESSURE TROUGH ALONG THE WEST COAST DEEPENS...A HIGH PRESSURE RIDGE WITH ITS AXIS ACROSS WESTERN WYOMING WILL LIMIT THE SNOWFALL BUT SOME OF THE PACIFIC MOISTURE WILL MAKE IT TO THE MOUNTAINS FRIDAY AND FRIDAY NIGHT. SATURDAY THE RIDGE AXIS WILL MOVE INTO THE NORTHERN AND CENTRAL HIGH PLAINS WITH MORE FAVORABLE SOUTHWEST FLOW MOVING OVER THE WEST. THIS WILL BRING INCREASED SNOWFALL TO THE WEST AND POTENTIAL STRONG WINDS EAST OF THE CONTINENTAL DIVIDE. SNOWFALL WILL BECOME MORE WIDESPREAD SATURDAY NIGHT AND SUNDAY IN THE WEST WITH VERY STRONG WEST SOUTHWEST WINDS IN THE EAST. THIS WILL ALSO BRING WARMING TEMPERATURES SATURDAY THROUGH SUNDAY. && .AVIATION.../00Z ISSUANCE/ WEST OF THE CONTINENTAL DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES VFR CONDITIONS WILL PREVAIL OVER SOUTHWEST WY THROUGH 06Z AT KRKS...KPNA...KBPI TERMINAL SITES. SCATTERED LIGHT SNOW WILL EXPAND FROM KJAC TO THE NORTH WITH MVFR/IFR CONDITIONS INCREASING ACROSS THE MOUNTAINS. THEN SNOW AND LOWERING CEILINGS WILL INCREASE OVER THE REST OF SOUTHWEST WY AFTER 06Z WITH MVFR/IFR CONDITIONS PREVAILING BY 15Z AT ALL TERMINAL SITES EXCEPT FOR KRKS WHICH SHOULD REMAIN VFR/MVFR THROUGH THE FORECAST PERIOD. EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KLND/KRIW/KWRL ROUTES VFR CONDITIONS WILL OCCUR THROUGH 18Z MONDAY AT ALL TERMINALS EXCEPT FOR KCOD WHICH WILL SEE MVFR CONDITIONS IN LOWER CIGS AND VISIBILITY REDUCTION DUE TO LIGHT SNOW BY 12Z MONDAY. WINDY CONDITIONS WILL OCCUR AT KCPR AIRPORT TONIGHT. AFTER 18Z...A STRONG COLD FRONT WILL RACE SOUTH ACROSS THE FORECAST AREA WITH SNOW AND STRONG NORTH WINDS FOLLOWING THROUGH THE END OF THE FORECAST PERIOD. && .FIRE WEATHER... FIRE DANGER LOW ACROSS THE FORECAST AREA TODAY THROUGH THE BEGINNING OF THE WORK. BREEZY WINDS WILL RETURN TO PORTIONS OF CENTRAL WYOMING THIS AFTERNOON AND EVENING...GUSTING OUT OF THE SOUTHWEST 20 TO 30 MPH. WHILE RH VALUES REMAIN RELATIVELY HIGH...THE WIND ACTIVITY MAY ENHANCE FIRE BEHAVIOR CONCERNS IN AREAS WITH LITTLE/NO SNOW COVER. OTHERWISE....MORE SNOW IS LIKELY ONCE AGAIN ACROSS THE WESTERN MOUNTAINS AND VALLEYS TODAY THROUGH TUESDAY EVENING...SPREADING EAST OF THE DIVIDE MONDAY AFTERNOON AND CONTINUING THROUGH WEDNESDAY MORNING. SOME AREAS EAST OF THE DIVIDE WILL SEE HEAVY SNOW AT TIMES. && .RIW WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH LATE TUESDAY NIGHT FOR WYZ030. WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH LATE TUESDAY NIGHT FOR WYZ008>011-017>020-022. WINTER WEATHER ADVISORY UNTIL 8 PM MST MONDAY FOR WYZ001-002-012- 013-023. WINTER WEATHER ADVISORY FROM 3 PM MONDAY TO 5 PM MST TUESDAY FOR WYZ015-016-026>029. WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 PM MST MONDAY FOR WYZ014-025. WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 11 PM MST MONDAY FOR WYZ024. WINTER WEATHER ADVISORY FROM NOON MONDAY TO 5 PM MST TUESDAY FOR WYZ004-007. WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY AFTERNOON FOR WYZ003-005-006. && SHORT TERM...BRAUN LONG TERM...C.BAKER AVIATION...BRAUN FIRE WEATHER...BRAUN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 314 PM MST SUN DEC 13 2015 WYZ001>020-022>030-142215- 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- 314 PM MST SUN DEC 13 2015 ...WINTER STORM WATCH FOR MUCH OF THE REGION EAST OF THE DIVIDE FROM MONDAY AFTERNOON THROUGH TUESDAY NIGHT...WINTER WEATHER ADVISORIES FILL THE REST OF THE GAPS INCLUDING SOUTHERN AND SOUTHWESTERN WYOMING... ...WINTER WEATHER ADVISORY FOR THE WESTERN MOUNTAINS AND VALLEYS FROM THIS AFTERNOON THROUGH MONDAY EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT LIGHT SNOW ACROSS THE WEST THIS MORNING...INCREASING IN COVERAGE AND INTENSITY THIS AFTERNOON AND EVENING. SNOW COULD BE HEAVY AT TIMES DURING THE EVENING COMMUTE OVER TETON PASS AND TOGWOTEE PASS. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY MONDAY THROUGH TUESDAY...SIGNIFICANT SNOWFALL WEST OF THE DIVIDE THROUGH MONDAY...SPREADING EAST OF THE DIVIDE LATER MONDAY AND TUESDAY. SNOW COULD BE HEAVY AT TIMES WITH STRONG NORTHERLY WIND. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY SNOWFALL AMOUNTS. THANK YOU.
The national radar mosaic for the moment the first event began.
10 winter storm. Local standard time, as filed.
Trained spotters reported from 6 to 12 inches of new snow across the Jackson Valley.
The public reported 8 inches of snow in Cody on Facebook.
Trained spotters reported anywhere from 8 to 14 inches across Thermopolis.
A trained spotter measured 32 inches of new snow on Casper Mountain. SNOTEL stations estimated anywhere from 23 to 27 inches of snow.
At the Lander airport 8.1 inches of snow was measured. Across the Lander foothills most areas had 6 to 9 inches of new snow.
A combination of moderate to heavy snow and winds gusting over 40 mph closed highway 20 26 from Shoshoni to the Fremont / Natrona county line.
A trained spotter measured 7 inches of snow at Sweetwater Station.
Heavy snow fell throughout much of Natrona County with the heaviest amounts closer to Casper Mountain. Amounts where generally 10 to 16 inches across the city of Casper with 9.5 inches at the Casper Airport. Lesser amounts fell in northern portions of the county with 5 to 6 inches at Midwest.
A combination of moderate to heavy snow and winds gusting up to 45 mph led to near whiteout conditions that led to the closure of Interstate 25 for several hours.
A combination of moderate to heavy snow and winds gusting to 40 mph led to the shutdown of Interstate 25 south of Buffalo for several hours.
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: 607268, 607263, 607267, 607260, 607265, 607264, 607266, 607259, 607262, 607261.