Strong winds in the upper atmosphere combined with a tight surface pressure gradient produced strong west to southwest winds over portions of southeast Wyoming.
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 CYS wrote it up.
Strong winds in the upper atmosphere combined with a tight surface pressure gradient produced strong west to southwest winds over portions of southeast Wyoming.
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 Cheyenne, WY wrote its last area forecast discussion before the first event at Apr 17, 2:48 AM MST, 1 hour 7 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 348 AM MDT SUN APR 17 2011 .SHORT TERM...TODAY THROUGH TUESDAY NIGHT GOES WATER VAPOR ANIMATION FEATURED A FAST WEST-NORTHWEST FLOW ALOFT (300 MB WIND MAX OF 110 KT OVER THE PACIFIC NORTHWEST)... WITH A SLUG OF MID/UPPER LEVEL MOISTURE PUSHING EAST INTO THE NORTHERN/CENTRAL ROCKIES. PRECIPITATION WAS RELEGATED TO EASTERN UTAH AND WESTERN WYOMING AS WELL AS FROM SOUTHERN MONTANA INTO THE WESTERN DAKOTAS. AT THE SURFACE...A STATIONARY FRONT WAS ORIENTED NORTHWEST TO SOUTHEAST FROM WESTERN MONTANA THROUGH EASTERN WYOMING...THE SOUTHERN NEBRASKA PANHANDLE INTO NORTHERN KANSAS. STRENGTHENING LOW/MID LEVEL WINDS WERE BEGINNING TO MIX DOWN TO THE SURFACE IN THE WIND PRONE CORRIDORS OF SOUTHEAST WYOMING. WIND GUSTS TO 50 MPH WERE COMMON BETWEEN CHEYENNE AND WHEATLAND...ALONG THE INTERSTATE 80 SUMMIT...AND NEAR ARLINGTON. THESE STRONG AND GUSTY WINDS WILL CONTINUE OVERNIGHT. THE 00Z NUMERICAL MODELS CONTINUE TO EXHIBIT SOME DIFFERENCES WITH RESPECT TO THE TIMING AND STRENGTH OF THE SHORTWAVE TROUGHS PROGGED TO AFFECT THE WESTERN CONUS THROUGH EARLY THIS WEEK. THE ZONAL FLOW ALOFT WILL MAINTAIN ITSELF TODAY THROUGH MONDAY WITH WEAK RIPPLES OF SHORTWAVE ENERGY ENHANCING THE LIFT FOR PRECIPITATION ACROSS THE CWA. THE ZONAL FLOW TRANSITIONS TO A MORE AMPLIFIED PATTERN AS SHORTWAVE ENERGY DIGS SOUTH INTO THE PACIFIC NORTHWEST MONDAY NIGHT...EAST ACROSS THE NORTHERN/CENTRAL ROCKIES TUESDAY AND THROUGH THE GREAT PLAINS TUESDAY NIGHT. THE STALLED SURFACE BOUNDARY WILL DRIFT NORTHEAST THIS MORNING...THEN SURGES SOUTHWARD INTO NEBRASKA AS A LOW PRESSURE SYSTEM MOVES SOUTHEAST ACROSS EASTERN WYOMING AND COLORADO. THE 300 MB 110+ KT JETLET OVER THE PACIFIC NORTHWEST WILL MOVE QUICKLY EAST...WITH SOUTHEAST WYOMING IN THE FAVORED RIGHT EXIT OR SINKING MOTION REGION. THE 00Z 700 MB WIND PROGS AND LOW/MID LEVEL WIND CORRIDOR GRADIENTS ARE SUPPORTIVE OF STRONG AND GUSTY WEST TO SOUTHWEST SURFACE WINDS OVER MUCH OF SOUTHEAST WYOMING TODAY THROUGH EARLY THIS EVENING. NOT EXPECTING HIGH WIND HIGHLIGHTS AT THIS TIME...BUT THE NEXT SHIFT WILL NEED TO MONITOR THIS SITUATION CLOSELY. 00Z NAM LIFTED INDICES SHOW MARGINAL INSTABILITY WITH VALUES OF 0 TO -2C WEST OF THE LARAMIE RANGE EARLY THIS AFTERNOON...SPREADING EAST INTO THE WESTERN NEBRASKA PANHANDLE. WILL CONTINUE ISOLATED THUNDERSTORM WORDING IN THE ZONE FORECAST THROUGH EARLY THIS EVENING WHEN THE LOW/MID LEVELS STABILIZE. LIKELY POPS WILL BE FOCUSED OVER THE SNOWY/SIERRA MADRE RANGES WITH CHANCE POPS ELSEWHERE THROUGH TONIGHT. THE SURFACE BOUNDARY WILL REMAIN DRAPED FROM CENTRAL THROUGH SOUTHEAST WYOMING MONDAY AND MONDAY NIGHT AS THE NEXT SURFACE LOW PRESSURE WAVE AND UPPER LEVEL SHORTWAVE MOVE EAST ACROSS WYOMING. AS A RESULT...PRECIPITATION COVERAGE WILL INCREASE THROUGHOUT THE CWA. THE SNOWY/SIERRA MADRE RANGES MAY SEE 3 TO 6 INCHES OF WET SNOW FROM SUNDAY NIGHT THROUGH MONDAY NIGHT. THE LAST IN A SERIES OF LOW PRESSURE WAVES WILL TRANSLATE EAST AND SOUTHEAST ALONG THE FRONT TUESDAY AND TUESDAY NIGHT WITH PRECIPITATION GRADUALLY TAPERING OFF FROM WEST TO EAST. ADDITIONAL SNOW ACCUMULATIONS OF 2 TO 3 INCHES WILL BE POSSIBLE TUESDAY FOR THE SNOWY/SIERRA MADRE RANGES. TEMPERATURES TODAY WILL QUITE MILD WITH HIGHS IN THE 50S AND 60S... WITH UPPER 30S AND 40S FOR THE LARAMIE AND SNOWY/SIERRA MADRE RANGES. COOLER AIR WILL INFILTRATE INTO THE NORTHERN PANHANDLE AND EASTERN WYOMING MONDAY WITH 40S AND 50S...WITH 60 TO 65 FOR THE SOUTHEAST CORNER OF THE CWA. MUCH COOLER TEMPERATURES WILL DOMINATE THE CWA TUESDAY IN THE WAKE OF A PACIFIC COLD FRONT...RANGING FROM THE 20S AND 30S HIGHER TERRAIN...TO THE 40S AND LOWER 50S LOWER ELEVATIONS. .LONG TERM...WEDNESDAY THROUGH SATURDAY. 00Z/17TH GFS AND ECMWF RUNS SHOW ZONAL...WEST TO EAST...FLOW ACROSS OUR COUNTIES AT 500 MB ON WEDNESDAY. BOTH MODELS SHOW UPPER FLOW BACKING TO SOUTHWEST ON THURSDAY AS TROUGHINESS CARVES OUT OVER THE GREAT BASIN...MORE AMPLIFIED ON THE GFS THAN THE ECMWF. CONFIDENCE WANES IN THEIR SOLUTIONS ON FRIDAY AS GFS HAS MODERATE 500 MB TROUGH ACROSS THE ROCKIES WHILE ECMWF MUCH LESS AMPLIFIED WITH BRISK SOUTHWEST FLOW ALOFT ACROSS WYOMING WHILE GFS FLOW IS MORE DIFFUSE. 00Z RUNS OF THE GFS AND ECMWF ALMOST COMPLETELY OUT OF PHASE AT 500 MB AT 00Z/SUNDAY WITH ECMWF SHOWING SOUTHWEST FLOW ALOFT ACROSS OUR COUNTIES AHEAD OF THE HIGH AMPLITUDE TROUGH ACROSS CALIFORNIA...WHILE GFS HAS LOW AMPLITUDE RIDGING ACROSS CALIFORNIA AND NORTHWESTERLY FLOW ALOFT ACROSS WYOMING. THUS...CONFIDENCE IN MODEL SOLUTIONS IS HIGH THROUGH THURSDAY...THEN LESS FRIDAY THROUGH THE WEEKEND. WEDNESDAY...SCATTERED SHOWERS AND A FEW THUNDERSTORMS IN THE AFTERNOON AND EVENING MAINLY WEST OF I-25 WITH ZONAL FLOW ALOFT AND ADEQUATE LOW AND MID LEVEL MOISTURE. THURSDAY...WILL SEE AN INCREASE IN AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS AS LOW AND MID LEVEL MOISTURE INCREASE AND FLOW ALOFT TURNS SOUTHWESTERLY AHEAD OF GREAT BASIN TROUGH. SURFACE LOW FORMS IN SOUTHEAST WYOMING WITH A CONVERGENCE AXIS EXTENDING NORTHWARD ALONG THE I-25 CORRIDOR ACTING AS A FOCUS FOR SHOWER AND THUNDERSTORM COVERAGE. FRIDAY...IF GFS VERIFIES...POTENT COLD FRONT SWEEPS THROUGH EARLY IN THE DAY WITH FALLING TEMPERATURES ACCORDING TO THICKNESS PROGS. WILL SEE SCATTERED SHOWERS WITH CYCLONIC FLOW ALOFT AND DECENT LOW AND MID LEVEL MOISTURE. SATURDAY...DRYING OUT WITH NORTHWEST FLOW ALOFT AND DECREASING LOW AND MID LEVEL MOISTURE. && .AVIATION...12Z TAFS. VFR PREVAILING. STRONG WEST WINDS ACROSS SOUTHEAST WYOMING ALONG AND WEST OF INTERSTATE 25 FROM 15Z TO 00Z WITH SUSTAINED WINDS 25 TO 40 KNOTS GUSTING LOCALLY NEAR 50 KNOTS...PRODUCING MOUNTAIN WAVE TURBULENCE AND LEE EDDY EFFECTS. SCATTERED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS PRODUCING LOCAL MVFR CEILINGS WITH TURBULENCE NEAR THUNDERSTORMS. SCATTERED TO NUMEROUS SHOWERS AFTER 06Z PRODUCING MVFR AND LOCALIZED IFR ESPECIALLY ALONG WEST FACING SLOPES OF THE MOUNTAINS. && .FIRE WEATHER... THE FIRE DANGER WILL BE LOW TO MODERATE FOR THE SOUTHEAST WYOMING AND WESTERN NEBRASKA PANHANDLE DISTRICTS FOR THE NEXT SEVERAL DAYS WITH GOOD CHANCES OF MEASURABLE PRECIPITATION. WINDS WILL BE STRONG AND GUSTY THROUGH EARLY THIS EVENING...HOWEVER MINIMUM RELATIVE HUMIDITIES WILL RANGE FROM 25 TO 45 PERCENT EAST OF THE LARAMIE RANGE. HUMIDITY RECOVERY AT NIGHT WILL BE GOOD TO EXCELLENT. && .HYDROLOGY... A FLASH FLOOD WATCH REMAINS IN EFFECT FOR SOUTHWEST CARBON COUNTY THROUGH FRIDAY AFTERNOON DUE TO A POTENTIAL DAM FAILURE AT THE LITTLE ROBBER DETENTION DAM...13 MILES NORTH OF BAGGS. REPAIRS TO THE DAM WILL NOT BE DONE UNTIL THAT TIME. RIVER LEVELS ON THE NORTH PLATTE RIVER DOWNSTREAM OF THE GUERNSEY RESERVOIR WILL REMAIN STEADY LEVELS TODAY...WITH SLIGHT RISES TONIGHT AND MONDAY...BEFORE RESUMING A SLOW FALL THROUGH THE MIDDLE OF THE WEEK. THE GAGE SITES AT HENRY AND MITCHELL NEBRASKA WILL REMAIN IN THE ACTION STAGE UNTIL FURTHER NOTICE. ADDITIONAL RELEASES FROM GUERNSEY RESERVOIR WILL CONTINUE...WITH MOST OF THE WATER DIVERTED TO IRRIGATION CANALS. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...FLASH FLOOD WATCH UNTIL 6 PM FRIDAY FOR WYZ111. NE...NONE. && SHORT TERM/FIRE WEATHER/HYDROLOGY...JAMSKI LONG TERM/AVIATION...RUBIN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHEYENNE WY 1044 AM MDT SAT APR 16 2011 WYZ101>119-171645- CONVERSE COUNTY LOWER ELEVATIONS-NIOBRARA COUNTY- NORTH LARAMIE RANGE-FERRIS/SEMINOE/SHIRLEY MOUNTAINS- SHIRLEY BASIN-CENTRAL LARAMIE RANGE AND SOUTHWEST PLATTE COUNTY- EAST PLATTE COUNTY-GOSHEN COUNTY-CENTRAL CARBON COUNTY- NORTH SNOWY RANGE FOOTHILLS-SOUTHWEST CARBON COUNTY- SIERRA MADRE RANGE-UPPER NORTH PLATTE RIVER BASIN-SNOWY RANGE- LARAMIE VALLEY-SOUTH LARAMIE RANGE-SOUTH LARAMIE RANGE FOOTHILLS- CENTRAL LARAMIE COUNTY-EAST LARAMIE COUNTY- 1044 AM MDT SAT APR 16 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL WYOMING... SOUTH CENTRAL WYOMING AND SOUTHEAST WYOMING. .DAY ONE...TODAY AND TONIGHT WINDY CONDITIONS WILL CONTINUE THROUGH THIS AFTERNOON WITH GUSTS UP TO 50 MPH. THE WINDS WILL DIMINISH THIS EVENING. ISOLATED THUNDERSTORMS MAY DEVELOP THIS AFTERNOON AND EARLY EVENING OVER EAST CENTRAL AND SOUTH CENTRAL WYOMING. CLOUD TO GROUND LIGHTNING...SMALL HAIL AND WIND GUSTS TO 50 MPH WILL BE POSSIBLE WITH THESE THUNDERSTORMS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY ISOLATED THUNDERSTORMS MAY DEVELOP SUNDAY AFTERNOON AND EARLY EVENING. COOLER TEMPERATURES WITH SCATTERED RAIN AND SNOW SHOWERS WILL RETURN TO THE AREA EARLY NEXT WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. && THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT... HTTP://WEATHER.GOV/CHEYENNE NEZ002-003-019>021-054-055-095-096-171645- DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-CHEYENNE- NORTH SIOUX-SOUTH SIOUX- 1044 AM MDT SAT APR 16 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA PANHANDLE. .DAY ONE...TODAY AND TONIGHT BREEZY CONDITIONS WILL DEVELOP LATE THIS MORNING AND CONTINUE THIS AFTERNOON...WITH GUSTS UP TO 25 MPH POSSIBLE. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY ISOLATED THUNDERSTORMS MAY DEVELOP SUNDAY AFTERNOON AND EARLY EVENING. COOLER TEMPERATURES WITH SCATTERED RAIN AND SNOW SHOWERS WILL RETURN TO THE AREA EARLY NEXT WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. && THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT... HTTP://WEATHER.GOV/CHEYENNE
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 138 AM MDT SUN APR 17 2011 WYZ106-110-116-117-171200- CENTRAL LARAMIE RANGE AND SOUTHWEST PLATTE COUNTY- NORTH SNOWY RANGE FOOTHILLS-SOUTH LARAMIE RANGE- SOUTH LARAMIE RANGE FOOTHILLS- INCLUDING THE CITIES OF...BORDEAUX...ARLINGTON...ELK MOUNTAIN... VEDAUWOO...BUFORD...PUMPKIN VINE...HORSE CREEK...HARRIMAN... WHITAKER 138 AM MDT SUN APR 17 2011 ...STRONG AND GUSTY WINDS OVERNIGHT... WEST TO SOUTHWEST WINDS HAVE INCREASED ACROSS THE WIND CORRIDORS BETWEEN CHEYENNE AND WHEATLAND...THE INTERSTATE 80 SUMMIT...AND NEAR ARLINGTON. GUSTS WERE BETWEEN 40 AND 50 MPH IN THESE AREAS. THESE STRONG WINDS WILL CREATE DIFFICULT CONDITIONS FOR LIGHTWEIGHT AND HIGH PROFILE VEHICLES. MOTORISTS TRAVELING IN THESE AREAS SHOULD BE PREPARED FOR SUDDEN CROSS WINDS AND REDUCE SPEEDS. JAMSKI
The national radar mosaic for the moment the first event began.
9 high wind. Local standard time, as filed.
WYDOT sensor at Bordeaux measured wind gusts of 58 mph or greater with a peak gust of 59 mph at 17/0410 MST.
WYDOT sensor at Bordeaux measured wind gusts of 58 mph or greater with a peak gust of 65 mph at 17/0605 MST.
UPR sensor at Emkay mesured sustained winds of 40 mph or greater with a peak gust of 72 mph at 17/0715 MST.
WYDOT sensor at Vedauwoo measured sustained winds of 40 mph or greater.
WYDOT sensor at Whitaker measured sustained winds of 40 mph or greater with a peak gust of 65 mph at 17/0730 MST.
WYDOT sensor at Bordeaux measured wind gusts of 58 mph or greater with a peak gust of 66 mph at 17/0735 MST.
WYDOT sensor at Halleck Ridge by Elk Mountain measured wind gusts of 58 mph or greater with a peak gust of 17/0725 MST.
ASOS wind sensor at Cheyenne measured sustained winds of 40 mph or greater with a peak gust of 64 mph at 17/0739 MST.
ASOS wind sensor at Cheyenne measured a gust of 64 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2011Every state in 2011This day in weather historyWarnings in Wyoming, April 2011
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: 295939, 295940, 295945, 295943, 295946, 295941, 295942, 295947, 295948.