A strong disturbance moved east into eastern Utah and western Colorado bringing strong southerly wind to Natrona and Johnson counties. S.
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.
A strong disturbance moved east into eastern Utah and western Colorado bringing strong southerly wind to Natrona and Johnson counties. Sustained southerly wind up to 46 mph was recorded for several hours along U.S. Highway 20/26 at Hiland and along Interstate 90 at the Indian Creek interchange. Gusts to 60 mph were also measured at Casper/Natrona County International 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 12, 2:30 AM MST, 2 hours 20 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 330 AM MDT THU APR 12 2012 .SHORT TERM...TODAY THROUGH SATURDAY NIGHT CONVECTIVE CELLS HAVE BEEN RACING FROM SOUTH TO NORTH ALL EVENING AND EARLY THIS MORNING...SOME WITH LIGHTNING AND STRONG SOUTH WINDS ABOVE 60 MPH...IN THE STRONG SOUTHERLY DIFLUENT FLOW AHEAD OF THE RAPIDLY APPROACHING NEGATIVELY TILTED TROUGH FROM THE SOUTHWEST. PRECIPITATION HAS BEEN MORE SOLID IN THE FAR WEST WHERE Q VECTOR FORCING MORE DIRECTLY TIED IN TO THE SHORTWAVE VORT ENERGY IS AIDING LIFT THERE. THE MAIN NEGATIVELY TILTED SHORTWAVE WILL TRACK NORTHEAST ACROSS THE CWA AROUND 12Z THURSDAY. SOUTHWEST WINDS OF 40 KNOTS AT THE BOUNDARY LEVEL AND 50 KNOT WINDS AT H7 WILL ACCOMPANY THIS TROUGH AROUND 12Z THIS MORNING PRIMARILY FROM EAST SLOPE OF THE WIND RIVER MTNS TO CPR AND AROUND CLARK IN PARK COUNTY SO WILL FORECAST STRONGER WINDS FOR THOSE AREAS THIS MORNING. LOW ELEVATION RAIN SHOWERS AND WESTERN AND MOUNTAIN SNOW SHOWERS THIS MORNING WILL BE ENHANCED IN SOUTHWESTERLY UPSLOPE FAVORED AREAS SUCH AS THE WEST SLOPE OF THE WIND RIVER MOUNTAINS AND SOUTHWEST YNP. A WEAKER SECONDARY TROUGH WILL PUSH THROUGH THE AREA THIS AFTERNOON. THE MAINLY UPSLOPE ENHANCED SHOWERS WILL TRANSITION TO CONVECTIVE SHOWERS THIS AFTERNOON AS THE SECOND TROUGH MOVES THROUGH ALONG WITH ISOLATED THUNDER WITH ASSOCIATED GUSTY WINDS AND SMALL HAIL. AN H7 CIRCULATION WILL BE EVIDENT OVER NE WY AROUND 00Z THIS EVENING WHERE ENHANCED PRECIP IS LIKELY IN JOHNSON COUNTY BY THEN. BY TONIGHT THE MAIN SHORTWAVE WILL RETROGRADE ACROSS THE WESTERN MONTANA BORDER AND INTO CANADA AS IT CLOSES OFF INTO A SMALL CIRCULATION AND BEGINS TO ROTATE AROUND THE KICKER LOW WHICH IS NOW AN ELONGATED CIRCULATION STILL OVER 45N/135W OFF THE NORTHERN CALIFORNIA COAST AND SHOULD BE JUST OFF THE CALIFORNIA AND OREGON COAST BY 06Z FRIDAY. SNOW TOTALS BY FRIDAY MORNING SHOULD AMOUNT TO 2 TO 4 INCHES ABOVE 8000 FEET ON THE WEST SLOPE OF THE WIND RIVER MOUNTAINS AND 5 TO 10 INCHES ABOVE 10K ALONG THE SPINE OF THE WIND RIVERS AS FAVORABLE SOUTHWESTERLY UPSLOPE SNOW FALLS THERE. 3 TO 6 INCHES OF SNOW IS EXPECTED ACROSS THE REST OF THE WESTERN MOUNTAINS WITH LOCAL AMOUNTS OF 7 TO 10 INCHES. 3 TO 10 INCHES IS EXPECTED ABOVE 9000 FEET IN THE BIG HORN MOUNTAINS. NOT QUITE ENOUGH TO WARRANT AN ADVISORY ANYWHERE. THE CIRCULATION ASSOCIATED WITH THE KICKER WILL BE TRACKING SOUTHEAST ACROSS NORTHERN CALIFORNIA BY 18Z FRIDAY AND THEN TRACK TO LAS VEGAS BY 12Z SATURDAY AND THEN THE FOUR CORNERS AREA BY 00Z SUNDAY. WITH THE AFOREMENTIONED LOWS SPINNING EACH OTHER FRIDAY...PLENTY OF SHOWER ACTIVITY WILL STILL BE AROUND IN SPITE OF THE MINOR RIDGING OVER THE AREA BETWEEN THE TWO SYSTEMS ALONG WITH ADDITIONAL CONVECTION. BY SATURDAY...SOUTHERLY DIFLUENT FLOW WILL OCCUR SATURDAY IN SOUTHERN WY AHEAD OF THE LOW OVER THE 4 CORNERS AREA WHERE THE LOW WILL BE VERTICALLY STACKED BETWEEN 700 AND 500MB. THIS WILL ENABLE PRECIP TO FALL OVER SOUTHERN WY SATURDAY AND SATURDAY NT. BY THEN A SURFACE LOW WILL DEVELOP IN NORTHEAST CO. ISENTROPIC LIFT WILL BE MOST PREVALENT WELL NORTH OF THE LOW FROM THE WIND RIVER BASIN TO THE SOUTHERN ABSAROKA MOUNTAINS SATURDAY. THESE DYNAMICS WILL SEED THE LOWER DECK OF CLOUDS ASSOCIATED WITH THE LOW LEVEL UPSLOPE EAST OF THE DIVIDE WRAPPING AROUND THE SFC LOW OVER NE CO. THE RESULTANT PRECIP WILL AFFECT MAINLY CENTRAL WY EAST OF THE DIVIDE PRIMARILY FROM LND TO CPR AS WELL AS THE EAST SLOPE OF THE WIND RIVER MTNS AND CASPER MTN SATURDAY THROUGH SATURDAY NIGHT. ON SATURDAY NIGHT...THE UPSLOPE FLOW WILL DEEPEN AS UPPER CYCLOGENESIS TAKES PLACE IN EASTERN SO. THE H7 TEMPS WILL BE AROUND -6C SAT AND SAT NIGHT. THE EAST SLOPE OF THE WIND RIVER MOUNTAINS WILL FAIR THE BEST FOR SNOW ACCUMULATIONS WHERE UPSLOPE AND ISENTROPIC LIFT WILL LIKELY WORK THE BEST THERE IN CONCERT ALONG WITH ACCUMULATING SNOW ALSO EXPECTED ON THE SOUTHERN ABSAROKA MOUNTAINS...BIG HORN MTNS AND CASPER MTN. THE LOWER ELEVATIONS IN THESE AREAS WILL SEE WET SNOW AND LIGHT ACCUMULATIONS WITH HIGHS IN THE 30S. RIGHT NOW IT APPEARS THAT THE WEEKEND SNOW EVENT WILL BE SOMEWHAT FAR REMOVED FROM THE STRONGEST ENERGY TO THE SOUTH OVER CO AND SOUTHEAST WY. ACCUMULATING SNOW WILL ALSO OCCUR IN THE WESTERN MTNS BUT TO A LESSER DEGREE ALONG WITH LIGHT SNOW ACCUMULATIONS IN WESTERN WY AS WELL AS SWEETWATER COUNTY SATURDAY AND SATURDAY NIGHT. BY SATURDAY...HIGHS WILL LIKELY BE 40 DEGREES COOLER EAST OF THE DIVIDE THAN THEY HAVE BEEN DURING THE LAST COUPLE OF DAYS. NORTH WINDS WILL PICK UP IN THE NORTH CENTRAL AND NORTHEAST ZONES LATE SATURDAY. .LONG TERM...SUNDAY THROUGH THURSDAY MODELS ARE IN REASONABLE AGREEMENT THROUGH THE MEDIUM RANGE PERIOD FOR AT LEAST THE BIG PICTURE. ON SUNDAY...WE STILL HAVE TO DEAL WITH OUR UPPER LOW EXPECTED TO BE RAPIDLY INTENSIFYING OVER NERN COLORADO AT SUNRISE SUNDAY. BLIZZARD CONDITIONS ARE QUITE POSSIBLE IN SERN WYOMING WITH OUR SERN ZONES BEING ON THE EDGE OF THE MORE SIGNIFICANT PRECIPITATION. WILL KEEP SUNDAY CHILLY IN OUR EASTERN ZONES ALONG WITH A DECENT SHOT OF AT LEAST MORNING SNOWFALL AND PROBABLY SOME PRETTY STRONG NORTH TO NORTHEAST WIND...HAVE INCREASED THE WINDS SIGNIFICANTLY SUNDAY MORNING WITH POTENTIAL FOR 25 TO 30 KNOT SUSTAINED WINDS AT LEAST. CONDITIONS SHOULD BEGIN IMPROVING LATE IN THE DAY BUT OVERALL IT SHOULD BE A CHILLY DAY WITH SNOW IN THE MORNING AND THEN GRADUAL IMPROVEMENT IN THE AFTERNOON BASED ON THE CURRENT TIMING. HIGHS WILL LIKELY BE VERY LATE IN THE DAY ACROSS THE ERN ZONES BUT HARD TO SEE THE 50 DEGREES THE BC GUIDANCE IS GIVING ME SO WILL KEEP THE COLDER FORECAST LIKE THE NEIGHBORS ALONG WITH SOME MORNING SNOW. AFTER THIS SYSTEM MOVES OFF SUNDAY NIGHT... WE HAVE TWO DISTURBANCES IN THE NW FLOW TO DEAL WITH ONE LATE MONDAY NIGHT INTO TUESDAY AND THEN ANOTHER WEDNESDAY NIGHT AND THURSDAY. THE MOUNTAINS WILL LIKELY SEE SOME SNOW WITH EACH OF THESE SYSTEMS WITH SOME INSTABILITY SHOWERS POSSIBLE IN BETWEEN THE MORE ORGANIZED PRECIPITATION. NOT MUCH ACROSS THE LOWER ELEVATIONS EAST OF THE DIVIDE BUT THE WEST WILL LIKELY SEE SOME LOWER ELEVATION RAIN WITH THE FIRST SYSTEM AND SOME COLD RAIN OR RAIN CHANGING TO SNOW WITH THE POTENTIALLY STRONGER WED NGT...THURSDAY SYSTEM. && .AVIATION.../12Z ISSUANCE/ VFR CONDITIONS WILL OCCUR OVER MOST AREAS TODAY AND TONIGHT. WEST OF THE DIVIDE AREAS OF MVFR CONDITIONS WILL OCCUR AS SNOW WILL OCCUR IN THE WESTERN MOUNTAINS AND SNOW AND RAIN SHOWERS WILL OCCUR IN THE WESTERN VALLEYS. THE PRECIPITATION WILL DECREASE OUT WEST AFTER 03Z. EAST OF THE DIVIDE SCATTERED RAIN SHOWERS WILL DEVELOP AFTER 18Z AND DECREASE AFTER 01Z THIS EVENING. GUSTY WIND WILL OCCUR IN MANY LOCATIONS THROUGH 00Z...THEN THE WIND WILL DECREASE AFTER 01Z. && .FIRE WEATHER... A VIGOROUS PACIFIC TROUGH WILL BE TRACKING NORTHEAST ACROSS WYOMING THIS MORNING. STRONG SOUTHWEST WINDS WILL ACCOMPANY THE TROUGH THIS MORNING. RAIN SHOWERS AND MOUNTAIN SNOW SHOWERS WILL ACCOMPANY THE TROUGH THIS MORNING. A SECONDARY TROUGH ALONG WITH MORE SHOWER ACTIVITY AS WELL AS ISOLATED THUNDERSTORMS ACCOMPANIED BY SMALL HAIL AND STRONG WIND GUSTS WILL OCCUR THIS AFTERNOON. TEMPERATURES WILL BE AROUND 20 DEGREES COOLER TODAY. COOL SHOWERY WEATHER WILL CONTINUE THROUGH FRIDAY OVER THE AREA WITH ISOLATED THUNDERSTORMS FRIDAY AFTERNOON. SNOW TOTALS BY FRIDAY MORNING SHOULD AMOUNT TO 2 TO 4 INCHES ABOVE 8000 FEET ON THE WEST SLOPE OF THE WIND RIVER MOUNTAINS AND 5 TO 10 INCHES ABOVE 10K ALONG THE SPINE OF THE WIND RIVERS AS FAVORABLE SOUTHWESTERLY UPSLOPE SNOW FALLS THERE. 3 TO 6 INCHES OF SNOW IS EXPECTED ACROSS THE REST OF THE WESTERN MOUNTAINS WITH LOCAL AMOUNTS OF 7 TO 10 INCHES. 3 TO 10 INCHES IS EXPECTED ABOVE 9000 FEET IN THE BIG HORN MOUNTAINS BY THIS FRIDAY MORNING. MORE WIDESPREAD PRECIPITATION IS LIKELY OVER THE WEEKEND WITH SNOW LEVELS REACHING THE VALLEY FLOOR EAST OF THE DIVIDE...PRIMARILY FROM LANDER TO CASPER. ACCUMULATING SNOW IS LIKELY IN THE MOUNTAINS OVER THE WEEKEND....ESPECIALLY EAST OF THE DIVIDE. HIGH TEMPERATURES SHOULD BE AS MUCH AS AROUND 40 DEGREES COOLER IN AREAS EAST OF THE DIVIDE SATURDAY. NORTH WINDS WILL PICK UP IN THE NORTH CENTRAL AND NORTHEAST ZONES LATE SATURDAY. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...LIPSON LONG TERM...SKRBAC AVIATION...AR FIRE WEATHER...LIPSON
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 513 AM MDT THU APR 12 2012 WYZ001>020-022>030-131200- 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- 513 AM MDT THU APR 12 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT SOUTHWEST WINDS OF 25 TO 35 MPH WITH GUSTS OF 40 TO 50 MPH ARE EXPECTED THIS MORNING ALONG THE SOUTHERN WIND CORRIDOR AND ALONG THE EAST SLOPE OF THE WIND RIVER AND ABSAROKA MOUNTAINS. SHOWERS AND THUNDERSTORMS WILL BECOME MORE WIDESPREAD ACROSS THE AREA WITH SNOW LEVELS LOWERING TO THE VALLEY FLOORS TODAY THROUGH FRIDAY MORNING. SMALL HAIL AND GUSTY WINDS ARE LIKELY. SNOW ACCUMULATION OF 2 TO 6 INCHES CAN BE EXPECTED IN THE MOUNTAINS WITH LOCAL AMOUNTS OF 7 TO 10 INCHES. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY SATURDAY AND SUNDAY...ACCUMULATING SNOW LIKELY IN THE MOUNTAINS ABOVE 7000 FEET. SNOW LEVELS ARE EXPECTED TO LOWER TO VALLEY AND BASIN FLOORS BY SATURDAY NIGHT...WHILE PRECIPITATION INCREASES EAST OF THE DIVIDE. SIGNIFICANT SNOWFALL IS POSSIBLE EAST OF THE DIVIDE BY SUNDAY...MAINLY ALONG THE EAST SLOPE OF THE WIND RIVER MOUNTAINS... ON CASPER MOUNTAIN AND POTENTIALLY EASTERN SWEETWATER COUNTY. STRONG NORTHEAST WINDS WILL ALSO ACCOMPANY THIS SNOW FROM ROCK SPRINGS TO CASPER. STAY TUNED FOR DETAILS ON THIS POTENTIAL SPRING STORM. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 345 AM MDT THU APR 12 2012 WYZ019-020-022-121600- CASPER MOUNTAIN-GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS- 345 AM MDT THU APR 12 2012 SOUTHWEST WINDS OF 25 TO 35 MPH WITH GUSTS OF 40 TO 50 MPH ARE EXPECTED THIS MORNING FROM THE GREEN MOUNTAINS TO CASPER. EXPECT STRONG CROSS WINDS ON AREA HIGHWAYS INCLUDING HIGHWAYS 287 FROM BEAVER RIM TO JEFFREY CITY...HIGHWAY 135 FROM BEAVER RIM TO SWEETWATER STATION...HIGHWAY 26 WEST OUT OF CASPER... INTERSTATE 25 NORTH AND SOUTH OF CASPER AND WYOMING BOULEVARD ALONG THE SOUTH SIDE OF CASPER. WYZ002-003-121600- ABSAROKA MOUNTAINS-CODY FOOTHILLS- 345 AM MDT THU APR 12 2012 SOUTHWEST WINDS OF 25 TO 35 MPH WITH GUSTS OF 40 TO 50 MPH ARE EXPECTED IN THE CODY FOOTHILL THIS MORNING. HOWEVER...SOME GUSTS OF 60 TO 65 MPH ARE EXPECTED IN THE VICINITY OF CLARK INCLUDING HIGHWAY 121 IN NORTHERN PARK COUNTY AS WELL AS ALONG THE CHIEF JOSEPH HIGHWAY OVER DEAD INDIAN PASS. WYZ015-121600- WIND RIVER MOUNTAINS EAST- 345 AM MDT THU APR 12 2012 SOUTHWEST WINDS OF 25 TO 35 MPH WITH GUSTS OF 40 TO 50 MPH ALONG WITH A FEW GUSTS OF 60 TO 65 MPH ARE EXPECTED ON THE EAST SLOPE OF THE WIND RIVER MOUNTAINS INCLUDING HIGHWAY 28 OVER SOUTH PASS. EXPECT SOME FALLING AND BLOWING SNOW TO ACCOMPANY THE WINDS THIS MORNING. LIPSON
The national radar mosaic for the moment the first event began.
4 high wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2012Every state in 2012This day in weather historyWarnings in Wyoming, April 2012
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: 368135, 368137, 368136, 368512.