An upper low over central Canada provided for a 24 to 36-hour stretch of unstable northwest flow aloft across Wyoming. This flow pattern favored heavy snow on the west side of the Bighorn Mountains and in the Nowood River Valley from Ten Sleep south to around Big Trails.
Every event with a place to put it; 4 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.
An upper low over central Canada provided for a 24 to 36-hour stretch of unstable northwest flow aloft across Wyoming. This flow pattern favored heavy snow on the west side of the Bighorn Mountains and in the Nowood River Valley from Ten Sleep south to around Big Trails. Snowfall in these areas topped one foot with other amounts of about 8 to 10 inches. Heavy snow of 6 to 8 inches also fell in Lander while the adjacent foothills of the Wind River Mountains received 12 to 14 inches.
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 Feb 20, 4:26 AM MST, 5 hours 34 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 426 AM MST FRI FEB 20 2015 .UPDATE...PUSHED UP START TIME WINTER STORM WARNING AND ADVISORIES TO BEGIN NOW IN NW WITH FIRST SHORTWAVE DIVING SE THE MT/ID BORDER...BANDS OF SNOW SHOWERS EXPECTED TO CONTINUE TO PUSH THROUGH THE AREA THROUGH MID-MORNING. && .PREV DISCUSSION... /ISSUED 328 AM MST FRI FEB 20 2015/ SHORT TERM...TODAY THROUGH SUNDAY NIGHT IMAGERY SHOWS GOOD UPR SW TROF JUST NOW BEGINNING TO ENTER THE NWRN FA...WITH ASSOCIATED WEAK SFC FRONT/TROF PUSHING INTO THE REGION JUST SOUTH OF THE MT/WY BORDER. SFC FRONTOGENESIS ALSO JUST STARTING ACROSS CNTRL MT. THE MAIN EVENT FOR THE NEXT COUPLE OF DAYS BEGINS THIS MORNING...ENDING BY MID DAY SUNDAY. MOST IF NOT ALL OF THE FA WILL SEE PRECIP/SNOW WITH THIS DISTURBANCE. HOWEVER...THE PRIMARY AREAS FOR SIGNIFICANT SNOWFALL WILL OCCUR ACROSS PORTIONS OF THE ABSAROKA ..BIGHORN...AND WIND RIVER MOUNTAINS TODAY THROUGH SAT NIGHT AND ALSO THE LANDER FOOTHILLS BEGINNING SAT MORNING. ADVISORY LVL SNOWFALL WILL ALSO START TODAY OVR YELLOWSTONE...THE CODY FOOTHILLS...SOUTH AND ALONG THE OWL CREEK AND BRIDGER MOUNTAINS. SUFFICIENT LL MOISTURE ALREADY IN PLACE ACROSS CNTRL AND NRN WY...WITH DEEPER EPAC MOISTURE ON ITS WAY INTO THE AREA...DECENT MID LVL FLOW TO START THINGS OFF...AND RELATIVELY QUICK FALLING TEMPS ALOFT WILL ALL COME TOGETHER TO PROVIDE A COMBINATION OF TERRAIN FORCED AND CONVECTIVE SNOWFALL FOR MUCH OF THE EVENT PERIOD...TRANSITIONING TO MORE SHALLOW STRATIFORM BY EARLY SUNDAY. LOW TO MID-LVL LAPSE RATES WILL INCREASE TO AROUND 7.5 DEG C/KM ACROSS THE AREA BY THIS AFTERNOON...THEN NEARLY 8 DEG C/KM BY SAT MORNING. AS THIS STORM SYSTEM EVOLVES...A COUPLE OF FRONTS WILL ALSO SWEEP THROUGH THE FA...ONE TODAY AND THE OTHER ON SATURDAY. THESE SFC TO MID LVL FRONTS WILL PROVIDE GOOD UPSLOPE FORCING TO 700MB EVEN WITH THE LOSS OF UPPER LVL FORCING THROUGH TIME. LL CONVERGENCE PROVIDED WITH THESE FRONTS WILL ALSO AID IN ENHANCING AREAS OF SNOWFALL FOR A TIME...ESPECIALLY OVR THE WRN AND SRN BIGHORN BASIN INCLUDING THE CODY FOOTHILLS...AND THE CNTRL/SRN PORTIONS OF THE WIND RIVER BASIN INCLUDING THE LANDER FOOTHILLS WHICH MAY SEE WARNING CRITERIA FOR SNOWFALL REACHED THROUGH THE DAY ON SATURDAY. MUCH OF THE REGION E OF THE DIVIDE MAY BE INCLUDED IN LATER WWAS TO START SAT MORNING AS THE SECOND FRONT DIVES SOUTH ACROSS THE REGION. WINTER STORM WATCHES HAVE BEEN UPGRADED TO WARNINGS...A NEW WS WATCH HAS BEEN ADDED FOR THE LANDER FOOTHILLS TO BEGIN SAT MORNING...AND WW ADVISORIES HAVE BEEN POSTED FOR YELLOWSTONE...THE CODY FOOTHILLS...AND THE BRIDGER AND OWL CREEK MOUNTAINS. MOST OF THE REST OF THE AREA...INCLUDING SWEETWATER COUNTY AND THE I80 CORRIDOR...THAT WILL NEED ADVISORIES CAN BE ADDED LATER TODAY OR TONIGHT AS THE BEST POTENTIAL FOR HEAVIER SNOWFALL WILL OCCUR ON SATURDAY OVER THESE AREAS. SO...WILL CONTINUE THE SPS(S) FOR THE THESE LOCATIONS THROUGH THE FIRST PERIOD OF THE FORECAST. LONG TERM...MONDAY THROUGH FRIDAY SYNOPSIS...A RIDGE OF HIGH PRESSURE WILL BRING DRY WEATHER WITH A WARMING TREND MONDAY AND TUESDAY. A CANADIAN COLD FRONT AND CHANCES OF SNOW WILL SPREAD SOUTH ACROSS THE AREA WEDNESDAY AND WEDNESDAY NIGHT FOLLOWED BY COLDER CONDITIONS THURSDAY WITH AREAS OF UPSLOPE SNOW ACROSS MAINLY THE CENTRAL AND SOUTH. NORTHWEST FLOW WILL SHIFT CHANCES OF SNOW TO THE WEST ON FRIDAY. DISCUSSION...MEDIUM RANGE GLOBAL MODELS IN GOOD OVERALL AGREEMENT WITH SYNOPTIC FEATURES THIS MORNING. UPPER RIDGE ALONG THE WEST COAST IS FORECAST TO FOLD OVER ACROSS THE NORTHERN ROCKIES ON MONDAY WITH WARM AIR ADVECTION FROM THE NORTH. THIS PATTERN IS USUALLY FAVORABLE FOR STEEP INVERSIONS AND FOG FORMATION...ESPECIALLY OVER FRESH SNOW COVER LEFT BY THIS WEEKEND'S STORM. PATCHY FOG ADDED TO CENTRAL BASINS AND WESTERN VALLEYS MONDAY MORNING WHERE OTHERWISE CLEAR SKIES ARE EXPECTED. THIS UPPER RIDGE ALONG THE WEST COAST IS EXPECTED TO COLLAPSE UNDER THE ASSAULT OF THE NEXT PACIFIC STORM SYSTEM MONDAY NIGHT AND TUESDAY...BEFORE THE RIDGE RE-ESTABLISHES FURTHER WEST ALONG 140W. GFS AND ECMWF HAVE NOT PUSHED THIS RIDGE QUITE AS FAR WEST AS THE LAST FEW RUNS. THAT NEXT PACIFIC STORM SYSTEM WILL DIVE SE ONTO THE NW COAST LATE TUESDAY...KICKING OUT A SW LOW OVER S AND CEN CA. IN ANOTHER NEAR REPEAT SCENARIO TO OUR LAST FEW SNOW EVENTS AND OUR UPCOMING ONE TODAY AND SATURDAY...THIS NEXT SYSTEM WILL CARVE OUT A LONGWAVE TROUGH ACROSS THE GREAT BASIN AND ROCKIES WEDNESDAY AND THURSDAY...AND PULL DOWN A CANADIAN COLD FRONT SOUTH ACROSS THE AREA LATE WEDNESDAY/WEDNESDAY NIGHT. ARCTIC SFC HIGH PRESSURE IS EXPECTED TO BUILD INTO THE NORTHERN PLAINS THURSDAY WITH N-NE UPSLOPE FLOW ACROSS CENTRAL AND EASTERN WYOMING...OR THURSDAY IS LOOKING A LOT LIKE OUR SETUP THIS SATURDAY. HOWEVER...WITH UPPER RIDGE SHIFTED A BIT FURTHER WEST THAN ITS CURRENT POSITION...COLD UPPER TROUGH IS EXPECTED TO REMAIN OVER THE NORTHERN ROCKIES INTO NEXT WEEKEND. UPSLOPE SNOW IS EXPECTED TO END EAST OF THE DIVIDE BY FRIDAY MORNING WITH COLD AND UNSETTLED NW FLOW SHIFTING THE BEST CHANCES OF SNOW ACROSS THE WEST. AVIATION.../12Z ISSUANCE/ EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES THERE WILL BE A WEATHER SYSTEM MOVING THROUGH THE REGION TODAY PRODUCING SNOW SHOWERS OVER THE MOUNTAINS WITH MVFR/IFR CONDITIONS. SOME TERMINAL SITES WILL EXPERIENCE SNOW SHOWERS TODAY INTO TONIGHT WITH A PERIOD OF MVFR TO IFR CONDITIONS. EXPECT FREQUENT MOUNTAIN OBSCURATION. A SECOND ROUND OF SNOW MOVES INTO NORTHERN WY AFTER 00Z SATURDAY AND SPREADS SOUTHWARD THROUGH 12Z SATURDAY. EXPECT CONDITIONS TO LOWER TO MVFR OR IFR. WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES A WEATHER SYSTEM WILL MOVE THROUGH THE AREA TODAY PRODUCING SNOW SHOWERS FOR MOST MOUNTAINS AND MVFR/IFR CONDITIONS. THE KJAC AND KPNA TERMINAL SITES WILL HAVE VCNTY SHOWERS FORECASTED BUT THERE MAY BE BRIEF PERIODS OF REDUCED VISIBILITY AND LOWER CEILINGS. GUSTY WIND AT KRKS THROUGH 00Z. CONDITIONS AT KJAC WILL LOWER TO MVFR PREVAILING BY 06Z SATURDAY. FIRE WEATHER... FIRE DANGER WILL REMAIN RELATIVELY LOW FOR ALL AREAS AS THE BEGINNING OF THE NEXT WINTER STORM SYSTEM MOVES THROUGH THE FORECAST AREA TODAY...REMAINING COLD AND SNOWY THROUGH SUNDAY. OTHERWISE...SMOKE DISPERSION TODAY WILL BE FAIR TO EXCELLENT ACROSS ALL FORECAST ZONES. && .RIW WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING UNTIL 5 PM MST SATURDAY WYZ002. WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM MST SATURDAY WYZ005-007. WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE SATURDAY NIGHT WYZ018. WINTER STORM WARNING FROM 11 AM THIS MORNING TO 5 AM MST SUNDAY WYZ008-009. WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 5 AM MST SUNDAY WYZ015. WINTER WEATHER ADVISORY UNTIL 5 AM MST SATURDAY WYZ001. WINTER WEATHER ADVISORY UNTIL 5 PM MST SATURDAY WYZ003. && UPDATE..AEM SHORT TERM...BRAUN LONG TERM...AEM AVIATION...AR FIRE WEATHER...BRAUN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 924 AM MST FRI FEB 20 2015 WYZ001>020-022>030-211300- 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- 924 AM MST FRI FEB 20 2015 ...WINTER STORM WARNINGS AND ADVISORIES ARE IN EFFECT FOR MUCH OF CENTRAL AND SOUTHEASTERN WYOMING THROUGH SUNDAY MORNING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT TURNING COLDER WITH PERIODS OF MODERATE TO HEAVY SNOW IN MANY LOCATIONS...ESPECIALLY IN THE CENTRAL AND NORTHERN MOUNTAINS OF WYOMING. SEE THE LATEST WINTER WEATHER PRODUCTS AND SPECIAL WEATHER STATEMENTS FOR FURTHER DETAILS. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY SATURDAY THROUGH SUNDAY MORNING...CONTINUED COLD WITH PERIODS OF MODERATE TO HEAVY SNOW EAST OF THE DIVIDE AND IN THE MOUNTAINS. SEE THE LATEST WINTER WEATHER PRODUCTS AND SPECIAL WEATHER STATEMENTS FOR FURTHER DETAILS. WEDNESDAY NIGHT AND THURSDAY...A CANADIAN COLD FRONT IS EXPECTED TO SPREAD SNOW SOUTH ACROSS THE AREA...WITH THE HIGHEST SNOWFALL AMOUNTS EXPECTED ALONG NORTH AND EAST FACING SLOPES ACROSS CENTRAL WYOMING ON THURSDAY. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT SNOW AMOUNTS. THANK YOU. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 544 AM MST FRI FEB 20 2015 WYZ006-202300- SOUTHEAST BIG HORN BASIN- 544 AM MST FRI FEB 20 2015 ...MORE SNOW AND COLD MOVING IN THIS AFTERNOON THROUGH SUNDAY... A COUPLE OF CANADIAN COLD FRONTS WILL THROUGH THE AREA TODAY THROUGH SUNDAY MORNING WITH SNOW DEVELOPING ALONG WITH BRISK NORTH WINDS AND COLDER TEMPERATURES. PERIODS OF SNOW WILL CONTINUE THROUGH SUNDAY. AREAS OF 2 TO 4 INCHES OF NEW SNOW CAN BE EXPECTED OVER THE WEEKEND. THE COMBINATION OF SNOW...WIND AND SLICK ROADS MAY BE A SIGNIFICANT IMPACT TO TRAVELERS AND OTHERS WITH OUTDOOR INTERESTS. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ028>030-202300- EAST SWEETWATER COUNTY-FLAMING GORGE-ROCK SPRINGS AND GREEN RIVER- 544 AM MST FRI FEB 20 2015 ...MORE SNOW AND COLD MOVING IN LATER THIS AFTERNOON THROUGH SUNDAY... A COUPLE OF CANADIAN COLD FRONTS WILL MOVE THROUGH THE AREA LATER THIS AFTERNOON AND EARLY...THEN AGAIN ON SATURDAY WITH SNOW DEVELOPING ALONG WITH BRISK NORTH WINDS AND COLDER TEMPERATURES. PERIODS OF SNOW WILL CONTINUE THROUGH SUNDAY. AREAS OF 2 TO 5 INCHES OF NEW SNOW CAN BE EXPECTED OVER THE WEEKEND. THE COMBINATION OF SNOW...WIND AND SLICK ROADS MAY BE A SIGNIFICANT IMPACT TO TRAVELERS AND OTHERS WITH OUTDOOR INTERESTS. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ024-027-202300- SALT RIVER AND WYOMING RANGES-SOUTH LINCOLN COUNTY- 544 AM MST FRI FEB 20 2015 ...COLD...WIND AND SNOW HEADED TO THE AREA LATER TODAY THROUGH SUNDAY... A COUPLE OF COLD FRONTS WILL MOVE THROUGH THE REGION LATER TODAY AND AGAIN ON SATURDAY. SOME LIGHT SNOW IS EXPECTED ACROSS THE AREA TODAY BEFORE A STRONG CANADIAN COLD FRONT MOVES IN FROM THE NORTHEAST WITH STEADIER SNOW AND BRISK WINDS. SNOWFALL OF 2 TO 4 INCHES IS EXPECTED IN THE LOWER ELEVATIONS WITH 5 TO 12 INCHES IN THE SALT AND WYOMING RANGES. THE COMBINATION OF SNOW...WIND AND SLICK ROADS MAY BE A SIGNIFICANT IMPACT TO TRAVELERS AND OTHERS WITH OUTDOOR INTERESTS. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ016-017-019-202300- GREEN MOUNTAINS AND RATTLESNAKE RANGE-UPPER WIND RIVER BASIN- WIND RIVER BASIN- 544 AM MST FRI FEB 20 2015 ...COLD...WIND AND SNOW HEADED TO THE AREA LATER TODAY THROUGH SUNDAY... A COUPLE OF CANADIAN COLD FRONTS WILL MOVE THROUGH THE AREA OVER THE NEXT COUPLE OF DAYS...WITH SNOW FIRST INITIATING THIS AFTERNOON. SNOWFALL OF 3 TO 6 INCHES ACROSS THE LOWER ELEVATIONS WITH HIGHER AMOUNTS IN THE MOUNTAINS. THE SNOW AND COLD WILL LIKELY HAMPER OUTDOOR ACTIVITIES AND TRAVEL. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ020-022-202300- CASPER MOUNTAIN-NATRONA COUNTY LOWER ELEVATIONS- 544 AM MST FRI FEB 20 2015 ...COLD...WIND AND SNOW HEADED TO THE AREA TODAY THROUGH SUNDAY... A COUPLE OF CANADIAN COLD FRONTS WILL MOVE DOWN FROM THE NORTH BEGINNING THIS AFTERNOON...INITIATING A PERIOD OF SNOW. SNOWFALL OF 2 TO 5 INCHES IN THE LOWER ELEVATIONS WITH 6 TO 12 INCHES IN THE IN THE SURROUNDING FOOTHILLS AND MOUNTAINS IS EXPECTED THROUGH SUNDAY MORNING. THE SNOW AND COLD WILL LIKELY HAMPER OUTDOOR ACTIVITIES AND TRAVEL. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ012-202300- TETON AND GROS VENTRE MOUNTAINS- 544 AM MST FRI FEB 20 2015 ...COLD...WIND AND SNOW HEADED TO THE LATER TODAY THROUGH SUNDAY... A COUPLE OF CANADIAN COLD FRONTS WILL MOVE DOWN FROM THE NORTH BEGINNING TODAY...INITIATING A PERIOD OF SNOW. SNOWFALL OF 2 TO 4 INCHES IS EXPECTED IN THE LOWER ELEVATIONS WITH 5 TO 12 INCHES IN THE MOUNTAINS. THE SNOW AND COLD MAY HAMPER SOME OUTDOOR ACTIVITIES AND TRAVEL. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. WYZ010-011-202300- NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY- 544 AM MST FRI FEB 20 2015 ...COLD...WIND AND SNOW HEADED TO THE AREA TODAY THROUGH SATURDAY... BANDS OF SNOW SHOWERS WILL CONTINUE TO PUSH THROUGH THE AREA THIS MORNING WITH SOME DECREASE IN ACTIVITY IN THE LATE MORNING AND AFTERNOON. A CANADIAN COLD FRONT WILL THEN SPREAD ANOTHER ROUND OF SNOW ACROSS THE AREA THIS EVENING WITH SNOW CONTINUING THROUGH SATURDAY MORNING BEFORE TAPERING OFF SATURDAY AFTERNOON. SNOWFALL OF 2 TO 5 INCHES IS EXPECTED BY SATURDAY EVENING. IN ADDITION... NORTH WIND WILL INCREASE TO 15 TO 30 MPH TONIGHT...CAUSING AREAS OF BLOWING AND DRIFTING SNOW AND LIMITED VISIBILITY THROUGH SATURDAY ALONG WITH BITTER COLD WIND CHILL TEMPERATURES. THE SNOW AND COLD WILL LIKELY HAMPER OUTDOOR ACTIVITIES AND TRAVEL. STAY TUNED FOR FURTHER STATEMENTS AND POSSIBLE WINTER HIGHLIGHTS AS THE TIME DRAWS NEARER. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
4 winter storm. Local standard time, as filed.
The SNOTEL site at Middle Powder River estimated 12 inches of new snow.
Heavy snow fell south of Ten Sleep. New snow measurements varied from 8 to almost 14 inches.
A trained spotter measured 14 inches of new snow 6 miles southwest of Lander near Sinks Canyon State Park.
The observer at the Lander airport measured 7.7 inches of new snow.
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, February 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: 554042, 554045, 556645, 554044.