A tight pressure gradient resulted as two areas of low pressure rotated around each other in eastern Montana. Northwest wind of 40 mph occurred over an extended period in northern Johnson County.
Every event with a place to put it; 2 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 tight pressure gradient resulted as two areas of low pressure rotated around each other in eastern Montana. Northwest wind of 40 mph occurred over an extended period in northern Johnson County. In the Big Horn Basin, sustained wind of 40 mph was recorded over a two hour period by the AWOS at Powell Municipal Airport.
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 Apr 30, 2:39 AM MST, 1 hour 31 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 339 AM MDT FRI APR 30 2010 .SHORT TERM...TODAY THROUGH SUNDAY NIGHT THE FOCUS OF THE SNOWFALL IS NOW CONCENTRATED OVER THE SOUTHERN BIG HORN AND BRIDGER MOUNTAINS. WILL LIKELY CANCEL THE ADVISORY FOR THE NW MTNS BUT JUST LEAVE IT UP FOR THE BIG HORN MTNS. SNOWFALL HAS BEEN MINIMAL IN NW WY DURING THE LAST SEVERAL HOURS. SATL LOOP INDICATES DRYING UPSTREAM TOWARD THE NW OVER MT. MEANWHILE ISENTROPIC LIFT WRAPPING AROUND THE LOW CURRENTLY OVER EASTERN MONTANA WILL CREATE ENOUGH SNOWFALL OVER THE BIG HORN MOUNTAINS TO WARRANT THE CONTINUATION OF THE SNOWFALL THERE THROUGH EARLY THIS MORNING. SNOW BANDING WILL CONTINUE OVER THE BIG HORN MTS THROUGH THE REST OF THE DAY TODAY. TWO ASSOCIATED 700MB LOWS WILL DUMBBELL AROUND EACH OTHER OVER THE NORTHERN PLAINS THIS EVENING. WHEN THE SECOND H7 LOW CIRCULATES SE ACROSS NORTH DAKOTA...A RESURGENCE OF SNOW BANDING WILL LIKELY OCCUR FROM THE BRIDGER AND SOUTHERN BIG HORN MTNS TO THE CASPER AREA THIS EVENING SO HAVE INDICATED ANOTHER ONE TO TWO INCHES OF SNOW FOR SOME OF THOSE AREAS. RAIN AND SNOW SHOWERS WILL CONTINUE SATURDAY IN NW WY AS THE STEERING WINDS BACK FROM THE NORTH TO THE MORE FAVORABLE NW FLOW ALONG WITH INCREASING INSTABILITY. AS THE TROUGH NOW OFF THE PAC COAST AT 150W TRACKS SOUTHEAST ACROSS WY...SNOWFALL WILL INCREASE IN NW WY AS WELL AS OVER THE BIG HORN MTNS SUNDAY MORNING. THE RAIN AND SNOW SHOWERS WILL CONTINUE SUNDAY AFTERNOON AND EVENING OVER NW WY AND THE BIG HORN MTNS UNDER FAVORABLE BACKING DIFLUENT FLOW. .LONG TERM...MONDAY THROUGH FRIDAY COLD FRONT TO MOVE INTO THE NORTHERN ROCKIES MONDAY WITH SHOWERS AND ISOLATED THUNDERSTORMS MOVING INTO THE WEST WITH MILD AND WINDY CONDITIONS ACROSS THE SOUTH AND CENTRAL. COLD FRONT MOVES ACROSS AREA MONDAY NIGHT WITH UNSEASONABLY COOL AND UNSETTLED WEATHER TO FOLLOW TUESDAY THROUGH FRIDAY. FORECAST CONTINUES TO BE WEIGHTED STRONGLY TOWARD CONSISTENT ECMWF SOLUTION OVER THE LAST SEVERAL RUNS WITH GFS SLOWLY STRUGGLING TO COME IN LINE OVER LAST COUPLE OF RUNS. UPPER TROUGH OVER CENTRAL PACIFIC THIS MORNING TO TRAVERSE GULF OF ALASKA OVER TOP OF EASTERN PACIFIC RIDGE OVER THE WEEKEND AND CARVE OUT NEW TROUGH ACROSS THE WESTERN U.S. EARLY NEXT WEEK...REPLACING CURRENT COLD TROUGH OVER THE ROCKIES. INCREASINGLY DIFLUENT FLOW BACKS AND STRENGTHENS AHEAD OF APPROACHING COLD FRONT MONDAY WITH COLD FRONT PUSHING INTO NORTHWEST WYOMING MONDAY AFTERNOON. THE POTENTIAL FOR DEVELOPMENT OF HIGH WIND EXISTS AHEAD OF THE FRONT ALONG THE EAST SLOPES OF THE DIVIDE AND FROM ROCK SPRINGS TO CASPER MONDAY AFTERNOON THROUGH TUESDAY MORNING AHEAD OF THE FRONT. RAIN AND SNOW SHOWERS/ISOLATED THUNDERSTORMS WITH SNOW LEVELS LOWERING TO VALLEY FLOORS INCREASE ACROSS THE NORTHWEST HALF MONDAY NIGHT. ECMWF LIFTS INITIAL SHORTWAVE INTO NORTHERN PLAINS TUESDAY WITH SECOND WAVE DIVING INTO NW U.S. BRINGING IN A BRIEF PERIOD OF DRYING TUESDAY NIGHT. THIS SECOND PIECE OF ENERGY MOVES ACROSS THE NORTHERN GREAT BASIN WEDNESDAY...AND ACROSS THE NORTHERN/CENTRAL ROCKIES THURSDAY. CONFIDENCE LOW AT THIS STAGE IN THE TIMING OF SMALLER FEATURES MOVING THROUGH THE LONGWAVE TROUGH...AND FORECAST GENERALLY KEEPS HIGH CHANCES OF PRECIPITATION AND UNSEASONABLY COOL TEMPERATURES ACROSS THE AREA WEDNESDAY AND THURSDAY. && .AVIATION... AN UPPER LOW OVER EASTERN MONTANA WILL SLOWLY PUSH EAST INTO DAKOTAS TODAY...SWINGING SOME MOISTURE AND ENERGY ACROSS THE COWBOY STATE. THIS WILL RESULT IN SCATTERED TO NUMEROUS SNOW SHOWERS ACROSS THE AREA...WITH AN EMPHASIS EAST OF THE DIVIDE. IFR CONDITIONS WILL BE COMMON OVER MOUNTAIN PASSES. PERIODS OF MVFR/IFR CONDITIONS WILL OCCUR TODAY IN THE LOWER ELEVATIONS...ESPECIALLY IN SNOW SHOWERS...ESPECIALLY OVER BIG HORN BASIN...JOHNSON AND NATRONA COUNTIES. STRONG WEST TO NORTH WINDS WILL CONTINUE OVER THE MAJORITY OF THE AREA TODAY. SNOW SHOWERS ARE EXPECTED TO BECOME ISOLATED BY LATE EVENING WITH IMPROVING CONDITIONS ACROSS THE REGION...WITH CLOUDS SCATTERING OUT IN MOST PLACES BY MIDNIGHT. && .FIRE WEATHER... SIGNIFICANT SNOWFALL WILL CONTINUE ACROSS THE BIG HORN MOUNTAINS THROUGH TODAY. RAIN AND SNOW SHOWERS WILL DECREASE ELSEWHERE. SNOW AND RAIN SHOWERS WILL OCCUR THROUGH THE WEEKEND ACROSS NORTHWEST WYOMING AND THE BIG HORN MOUNTAINS WITH THE INFLUENCE OF A MOIST NORTHWEST FLOW. TEMPERATURES WILL REMAIN UNSEASONABLY COOL THROUGH THE PERIOD. && .RIW WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING WYZ008-009. && SHORT TERM...LIPSON LONG TERM...AEM AVIATION...WM FIRE WEATHER...LIPSON
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MDT FRI APR 30 2010 WYZ001>020-022>030-011100- 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 FRI APR 30 2010 ....WINTER WEATHER ADVISORY IN EFFECT TODAY FOR THE BIG HORN MOUNTAINS... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT NORTH TO NORTHWEST FLOW OF MOIST AIR ACROSS THE BIGHORN MOUNTAINS TODAY WILL BRING SIGNIFICANT SNOWFALL TO THE AREA. A TOTAL OF 8 TO 12 INCHES OF SNOW IS LIKELY IN THE BIGHORN MOUNTAINS BY EARLY THIS EVENING WITH LOCALLY HIGHER AMOUNTS POSSIBLE. AN UNSETTLED WEATHER PATTERN WILL KEEP SNOW GOING IN THE NORTHERN MOUNTAINS AT TIMES INTO THE UPCOMING WEEKEND WITH THE POSSIBILITY OF MODERATE ACCUMULATIONS. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY A STRONG COLD FRONT IS FORECAST TO MOVE THROUGH THE AREA MONDAY NIGHT AND TUESDAY BRINGING THE POTENTIAL FOR HIGH WIND ACROSS THE AREA ALONG WITH ANOTHER ROUND OF SIGNIFICANT SNOWFALL IN THE MOUNTAINS. ISOLATED THUNDERSTORMS WILL LIKELY ALSO ACCOMPANY THIS COLD FRONTAL PASSAGE. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT SNOWFALL TODAY AND TONIGHT. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
2 high wind. 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, April 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: 222708, 222706.