A strong, moisture rich Pacific storm system moved south of Wyoming, creating favorable conditions for heavy upslope snowfall in areas east of the Continental Divide. Up to 39 inches of snow fell in the southern Wind River Mountains, and a foot of snow fell in adjacent areas of the Wind River Basin.
Every event with a place to put it; 9 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, moisture rich Pacific storm system moved south of Wyoming, creating favorable conditions for heavy upslope snowfall in areas east of the Continental Divide. Up to 39 inches of snow fell in the southern Wind River Mountains, and a foot of snow fell in adjacent areas of the Wind River Basin. Significant snow also fell in the southern Absaroka Range and southern Bighorn Mountains.
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 May 10, 2:42 AM MST, 18 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 342 AM MDT MON MAY 10 2010 .SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT SHOWER ACTIVITY CONTINUES TO IMPACT MUCH OF CENTRAL WYOMING THIS MORNING. PERIODS OF SHOWER ACTIVITY ARE EXPECTED TO REMAIN OVER MUCH OF CENTRAL...WESTERN AND SOUTHERN WYOMING FOR THE NEXT COUPLE OF DAYS DUE TO A SERIES OF SYSTEMS IMPACTING THE STATE. THE FIRST OF THESE SYSTEMS...A WAVE OF LOW PRESSURE ALREADY IMPACTING THE CWA WILL MOVE OUT OF THE AREA LATE THIS EVENING. A VERY BRIEF TRANSITORY RIDGE WILL DEVELOP OVER THE AREA DURING THE OVERNIGHT HOURS...ALLOWING SOME AREAS TO SEE DECREASED PRECIPITATION THROUGH THE EARLY MORNING HOURS OF TUESDAY. THE NEXT SYSTEM IS A STRONG AREA OF LOW PRESSURE WHICH WILL MOVE OFF THE CALIFORNIA COAST EARLY TUESDAY MORNING AND QUICKLY MOVE TOWARDS THE STATE. THIS SECOND SYSTEM IS EXPECTED TO HAVE MUCH MORE IMPACT OVER THE STATE...ESPECIALLY AS IT INCREASES SHOWER ACTIVITY OVER UPSLOPE FAVORED AREAS TUESDAY MORNING. THIS SYSTEM...WHICH WILL DRAMATICALLY COOL H7 TEMPERATURES ACROSS THE AREA WILL KEEP SHOWER ACTIVITY ACROSS THE AREA THROUGH WEDNESDAY AFTERNOON. AS THE SYSTEM MOVES EASTWARD...IT IS EXPECTED TO MOVE ALONG THE SOUTHERN THIRD OF THE CWA WITH POTENTIALLY SIGNIFICANT SNOWFALL ACCUMULATIONS EXPECTED OVER THE CENTRAL MOUNTAINS AND VALLEYS. WINTER STORM WATCHES HAVE BEEN ISSUED TO ACCOUNT FOR THIS POTENTIALLY SIGNIFICANT SNOWFALL. THE UPSLOPE FAVORED AREAS WILL SEE SNOWFALL BEGIN TUESDAY MORNING...WITH THE CENTRAL BASINS AND CASPER MOUNTAINS EXPERIENCING INCREASED SNOWFALL TUESDAY AFTERNOON. SEE ISSUED WINTER WEATHER HIGHLIGHTS FOR FURTHER DETAILS PERTAINING TO POTENTIAL SNOWFALL AMOUNTS AND TIMING RELATING TO THIS SYSTEM. IN GENERAL...BOTH SYSTEM WILL LEAVE COOLER TEMPERATURES ACROSS THE CWA THROUGH WEDNESDAY. GUSTY NORTHEAST WIND MAY ACCOMPANY THE SECOND SYSTEM WHICH MAY CREATE BLOWING AND DRIFTING SNOW AND REDUCED VISIBILITIES. .LONG TERM...THURSDAY THROUGH MONDAY COOL...UNSTABLE AIRMASS REMAINS OVER THE AREA THURSDAY WITH ISOLATED TO SCATTERED RAIN AND SNOW SHOWERS. WARMING DRYING TREND FOLLOWS FRIDAY AND OVER THE WEEKEND WITH TEMPERATURES NEAR OR SLIGHTLY ABOVE NORMAL SUNDAY AND MONDAY. MEDIUM-RANGE MODELS CONTINUE TO SHOW OVERALL TREND TOWARD SLOWER PROGRESSION OF UPPER TROUGH OUT OF THE ROCKIES THURSDAY AND FRIDAY WITH BOTH GFS AND ECMWF SHOWING WEAK SHORTWAVES IN NORTHERLY FLOW OVER WYOMING THURSDAY BEHIND MAIN UPPER LOW...WITH COOL N-E UPSLOPE FLOW LINGERING IN THE LOWER LEVELS. FORECAST MAINTAINS SCATTERED RAIN AND SNOW SHOWERS OVER MOUNTAINS AND UPSLOPE FAVORED AREAS WITH TEMPERATURES ON THE COOL SIDE OF GUIDANCE. REMNANTS OF UPPER TROUGH CONTINUE TO SLOWLY FILL THROUGH FRIDAY WITH AIRMASS DRYING OUT AND WARMING. GFS AND TO A GREATER EXTENT...ECMWF...SHOW SPLIT FLOW DEVELOPING ALONG THE WEST COAST OVER THE WEEKEND WITH LESS AMPLIFICATION OF RIDGE OVER THE ROCKIES RESULTING IN LOWER HEIGHTS AND NOT QUITE THE WARMING TREND SEEN IN PREVIOUS RUNS. FORECAST CONTINUES TO PREFER LESS PROGRESSIVE ECMWF OVER THE EASTERN PACIFIC AND LESS RIDGING OVER ROCKIES OVER THE WEEKEND INTO EARLY NEXT WEEK. HOWEVER...A SIGNIFICANT WARMING TREND IS STILL IN STORE OVER THE WEEKEND RELATIVE TO THE NEXT FEW DAYS. MODELS AGREE ON CONTINUED AMPLIFICATION OF RIDGE OVER ROCKIES AND GREAT PLAINS EARLY NEXT WEEK AS TROUGH SHARPENS OVER EASTERN PACIFIC. WARMING TREND CONTINUES INTO EARLY NEXT WEEK WITH MOSTLY DRY CONDITIONS AS HEIGHTS CONTINUE TO BUILD OVER THE ROCKIES. && .AVIATION... THE FIRST OF TWO STORM SYSTEMS WILL AFFECT THE AREA TODAY...BEFORE THE NEXT ONE BEGINS TO AFFECT THE WEST LATE TONIGHT. WIDESPREAD MVFR CEILINGS WITH AREAS OF IFR CEILINGS/VISIBILITIES IN PRECIP ARE LIKELY...ESPECIALLY OVER JOHNSON...FREMONT AND NATRONA COUNTIES TODAY...BUT ALL AREAS HAVE A DECENT CHANCE FOR PERIODS OF MVFR CONDITIONS WITH LCL IFR CONDITIONS IN PRECIP. MOUNTAINS WILL BE OBSCURED. HAVE HIT KCPR...KRIW...KLND TAFS THE HARDEST WITH PRECIP/WORSE CONDITIONS. CONDITIONS ARE EXPECTED TO IMPROVE SOMEWHAT BY MID TO LATE AFTERNOON...ESPECIALLY EAST OF THE DIVIDE AS THE FIRST SYSTEM EXITS THE AREA. AT THE SAME TIME AREAS WEST OF THE DIVIDE WILL BEGIN TO DETERIORATE LATE AFTERNOON INTO THE EVENING AS THE SECOND STORM SYSTEM APPROACHES. THE RAIN/SNOW ELEVATION WILL VARY FROM 5000 TO 6500 FT MSL TODAY...EAST OF THE DIVIDE...AND 6500 TO 7500 FT MSL WEST OF THE DIVIDE AND OVER SWEETWATER COUNTY. NORTH TO NORTHEAST WINDS OF 10-20KTS WILL BE COMMON TODAY...WITH WINDS WEAKENING OVERNIGHT. && .FIRE WEATHER... SHOWER ACTIVITY WILL REMAIN OVER PORTIONS OF THE FORECAST AREA FOR THE NEXT FEW DAYS. TUESDAY WILL SEE A POTENTIALLY STRONG AREA OF LOW PRESSURE IMPACTING THE STATE...WHICH WILL CREATE INCREASED AREAS OF SNOWFALL. SNOW LEVELS ARE EXPECTED TO DECREASE THROUGHOUT TUESDAY WITH PERIODS OF POTENTIALLY HEAVY SNOWFALL ANTICIPATED ACROSS THE CENTRAL MOUNTAINS. WINTER WEATHER HIGHLIGHTS HAVE BEEN ISSUED FOR PORTIONS OF CENTRAL WYOMING. PLEASE VISIT THE WINTER STORM PRODUCT...WSWRIW...FOR DETAILS CONCERNING THIS UPCOMING SYSTEM. POOR SMOKE DISPERSAL GENERALLY EXPECTED TODAY...THOUGH INCREASING WIND ON TUESDAY WILL BRING PERIODS OF GOOD TO FAIR SMOKE DISPERSAL. && .RIW WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY AFTERNOON WYZ017-019-020-022. WINTER STORM WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY AFTERNOON WYZ015-016-018. && SHORT TERM...BRANHAM LONG TERM...AEM AVIATION...WM FIRE WEATHER...BRANHAM
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MDT SUN MAY 9 2010 WYZ001>020-022>030-101100- 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 MDT SUN MAY 9 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY SNOWFALL COVERAGE IS EXPECTED TO INCREASE TUESDAY AS AN AREA OF LOW PRESSURE IMPACTS THE STATE. THIS SYSTEM WILL INTRODUCE ENHANCED UPSLOPE SNOWFALL TO THE CENTRAL MOUNTAINS. SNOWFALL...WHICH WILL CONTINUE THROUGH WEDNESDAY MAY BE HEAVY AT TIMES WITH POTENTIALLY SIGNIFICANT ACCUMULATIONS EXPECTED BY WEDNESDAY EVENING. IN ADDITION TO THE UPSLOPE FAVORED AREAS...SOUTHERN WYOMING INCLUDING SWEETWATER AND LINCOLN COUNTIES APPEAR FAVORABLE FOR THE HEAVIER SNOWFALL AMOUNTS. STRONG EASTERLY WIND MAY RESULT IN BLOWING AND DRIFTING SNOW WITH LATE SEASON WINTER DRIVING CONDITIONS ACROSS SOUTH PASS AND THE INTERSTATE 80 CORRIDOR TUESDAY AND WEDNESDAY. ROADS AND HIGHWAYS ARE LIKELY TO BECOME SLUSHY OR SNOW-PACKED ABOVE 6000 FEET WITH MAINLY WET ROADS EXPECTED BELOW 6000 FEET ON TUESDAY AND WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
9 heavy snow. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2010Every state in 2010This day in weather historyWarnings in Wyoming, May 2010
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: 229247, 229241, 229248, 229243, 229157, 229242, 229246, 229245, 229244.