Strong outflow winds from dissipating evening thunderstorms produced wind gusts to 63 mph in central Carbon County.
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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 outflow winds from dissipating evening thunderstorms produced wind gusts to 63 mph in central Carbon County.
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 Aug 15, 1:24 PM MST, 5 hours 32 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 224 PM MDT MON AUG 15 2011 .SHORT TERM...TONIGHT THROUGH WEDNESDAY... THE 18Z SURFACE ANALYSIS SHOWED LOW PRESSURE STRETCHING ACROSS MONTANA INTO THE DAKOTAS. ALSO A TROUGH EXTEND NORTH TO SOUTH FROM AROUND RAPID CITY TO NEW MEXICO WITH FAIRLY DRY WEST OF THIS FEATURE AND TO THE EAST 55+ DEW POINTS. A WEAK COLD FRONT WAS LOCATED IN THE PACIFIC NORTHWEST AND WAS ASSOCIATED WITH AN UPPER SYSTEM WITH HEIGHT FALLS IN EXCESS OF 50 METERS AT 5H. THIS COLD FRONT WILL BE THE FOCUS OF THE SHORT TERM AND HOW FAR TO THE SOUTH IT WILL BE ABLE TO MOVE. SATELLITE IMAGERY SHOWS THIS FEATURE SWINGING SOUTHEASTWARD. OVERHEAD PICTURES ARE SHOWING MAINLY CLEAR SKIES WITH JUST A FEW CUMULUS CLOUDS BEGINNING TO SHOW UP. QUESTION BECOMES HOW FAR INTO THE CWA WILL THIS FRONT MAKE IT AS THE UPPER SUPPORT MOVES EAST ALONG THE CANADIAN BORDER. THICKNESS VALUES WOULD INDICATE IT MOVES INTO THE NORTHERN CWA BY 12Z TUESDAY BUT THEN LOSES ITS PUSH AND BECOMES STATIONARY BY 18Z GENERALLY ALONG A LINE FROM CHADRON TO RAWLINS. HOWEVER THE SURFACE PRESSURE FORECAST WOULD SUGGEST THE FRONT FURTHER SOUTH NEAR THE COLORADO BORDER AT THIS SAME TIME. REGARDLESS THERE APPEARS TO BE LITTLE MOISTURE AVAILABLE AND ALTHOUGH ISOLATED SHOWERS MAY DEVELOP ONLY SMALL POPS WILL BE REQUIRED. BY WEDNESDAY HOWEVER THE SURFACE HIGH SETTLES DOWN OVER THE MIDWEST AND BEGINS TO GIVE THE CWA RETURN FLOW. AT THIS TIME SPC HAS THE PANHANDLE IN A SLIGHT RISK WHICH WOULD APPEAR TO MAKE SENSE. TEMPERATURE WISE TUESDAY PROBABLY WILL END UP BEING A LITTLE COOLER PROBABLY 5 TO 10 DEGREES BUT JUMP RIGHT BACK UP ON WEDNESDAY. .LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...UPPER LEVEL RIDGE WILL BUILD OVER THE GREAT BASIN ON WEDNESDAY NIGHT AND THURSDAY WITH DRY WESTERLY FLOW ALOFT. A FRONTAL BOUNDARY LOOKS TO MOVE SOUTH ACROSS THE EASTERN ZONES THURSDAY AFTERNOON AND EVENING. GUSTY WEST TO NORTHWEST WINDS AHEAD OF THE FRONT WILL COMBINE WITH DRY CONDITIONS TO HEIGHTEN FIRE WEATHER CONCERNS ACROSS MUCH OF THE FORECAST AREA THURSDAY AFTERNOON...INCLUDING THE NEBRASKA PANHANDLE. WINDS WILL SHIFT TO THE NORTH BEHIND THE FRONT THEN BACK TO A MORE EASTERLY DIRECTION BY FRIDAY AFTERNOON. LOOKS LIKE NOT MUCH TEMP CHANGE FROM THURSDAY TO FRIDAY AS THE UPPER RIDGE CONTINUES TO BUILD OVERHEAD AND KEEPS THICKNESSES HIGH. A SHORTWAVE MOVING ACROSS IN WESTERLY FLOW ALOFT COMBINED WITH THIS MORE UPSLOPE FLOW WILL INCREASE PRECIP CHANCES MAINLY ACROSS THE EASTERN ZONES WHERE LLVL MOISTURE IS MORE PROMINENT. SATURDAY AND BEYOND...MODELS TEND TO SHOW AGREEMENT WITH THE UPPER PATTERN BUT DIFFER WITH THE SURFACE REFLECTION. WILL SEE AN UPPER TROUGH DIG INTO NORTHERN CALIFORNIA THROUGH THE WEEKEND WITH VARYING DEGREES OF RIDGE AMPLIFICATION ACROSS THE ROCKIES. IN GENERAL...TEMPERATURES WILL REMAIN VERY WARM WITH MOSTLY DRY CONDITIONS THROUGH THE WEEKEND. THE GFS SHOWS A DEEPER PLUME OF MONSOONAL MOISTURE MOVING ACROSS THE AREA ON SUNDAY AS WELL AS STRONGER UPSLOPE FLOW VS THE ECMWF...SO COULD SEE A RETURN OF THUNDERSTORMS FOR SUNDAY AND POSSIBLY MONDAY. AT THIS POINT CONFIDENCE IS LOW SO WILL KEEP LOW END SLIGHT CHANCE FOR SUNDAY WITH JUST SOME INCREASING CLOUDINESS FOR MONDAY. && .AVIATION...18Z TAF ISSUANCE...VFR CONDITIONS WILL PREVAIL ACROSS THE FORECAST AREA...WITH GUSTY WESTERLY WINDS UP TO 30KTS ALONG AND WEST OF THE LARAMIE RANGE THIS AFTERNOON. STILL EXPECT VCTS NEAR KRWL WITH MAINLY HIGH CB NEAR KLAR AND KCYS. A FRONT WILL DROP FROM NORTH TO SOUTH ACROSS THE EASTERN PLAINS TUESDAY MORNING AFTER 09Z WITH WINDS SHIFTING TO THE NORTH AND GUSTING TO 25 KTS IN ITS WAKE. DO NOT EXPECT MUCH MORE THAN SCT MID CLOUDS WITH THE FRONT. WINDS WILL EVENTUALLY EASE THROUGH THE LATER MORNING HOURS. && .FIRE WEATHER...NEW FUEL STATUS OUT THIS MORNING AND CONTINUES TO SHOW ONLY FIRE WEATHER ZONES 301...302 AND 306 IN WYOMING AS WELL AS THE PANHANDLE HAVING FUELS CONDUCIVE FOR LARGE FIRE GROWTH. THE PANHANDLE WILL HAVE NO WORRIES AS RELATIVE HUMIDITY READINGS WILL BE MUCH TOO HIGH FOR ANY ISSUES. HOWEVER IN 301 AND 302 WILL CONTINUE TO BE BORDER LINE AS WHETHER HIGHLIGHTS ARE REQUIRED AND SHOULD BE MONITORED CLOSELY THIS AFTERNOON. TOMORROW A SLIGHT INCREASE IN THE RELATIVE HUMIDITIES SHOULD KEEP CRITICAL VALUES AT BAY. WEDNESDAY THESE AREAS WILL ONCE AGAIN SEE RELATIVE HUMIDITIES IN THE MID AND UPPER TEENS BUT WINDS WILL BE LOW ENOUGH TO PRECLUDE ANY HIGHLIGHTS. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && SHORT TERM/FIRE WEATHER...GRIFFITH LONG TERM/AVIATION...RJM
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHEYENNE WY 415 PM MDT MON AUG 15 2011 WYZ101>119-161015- 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- 415 PM MDT MON AUG 15 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL WYOMING... SOUTH CENTRAL WYOMING AND SOUTHEAST WYOMING. .DAY ONE...THIS AFTERNOON AND TONIGHT ISOLATED THUNDERSTORMS WILL CONTINUE OVER MUCH OF SOUTHEAST WYOMING THROUGH THE EVENING. MANY OF THESE STORMS WILL PRODUCE BRIEF WIND GUSTS BETWEEN 45 AND 55 MPH. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY A FRONTAL BOUNDARY IS EXPECTED TO PUSH THROUGH THE AREA ON TUESDAY AND BRING ANOTHER CHANCE OF THUNDERSTORMS TO THE REGION. SOME OF THE STORMS MAY BECOME STRONG AND PRODUCE GUSTY WINDS AND SMALL HAIL. GUSTY WEST WINDS AND VERY DRY RELATIVE HUMIDITIES COULD DEVELOP ON THURSDAY. THIS COULD FAVOR RED FLAG CONDITIONS FOR PORTIONS OF THE AREA. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED THIS AFTERNOON 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>021-054-055-095-096-161015- DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-CHEYENNE- NORTH SIOUX-SOUTH SIOUX- 415 PM MDT MON AUG 15 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA PANHANDLE. .DAY ONE...THIS AFTERNOON AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY A FRONTAL BOUNDARY IS EXPECTED TO PUSH THROUGH THE AREA ON TUESDAY AND BRING A CHANCE OF THUNDERSTORMS TO THE REGION. SOME OF THE STORMS MAY BECOME STRONG AND PRODUCE GUSTY WINDS UP TO 50 MPH AND SMALL HAIL. THE THUNDERSTORM CHANCES COULD LINGER INTO WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED THIS AFTERNOON AND TONIGHT. && THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT... HTTP://WEATHER.GOV/CHEYENNE WEILAND
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
502 PM MDT MON AUG 15 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0443 PM TSTM WND GST COW CREEK 43.25N 104.62W
08/15/2011 M48 MPH NIOBRARA WY PARK/FOREST SRVC
&&
MWEILANDSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 510 PM MDT MON AUG 15 2011 WYZ109-110-112>114-152345- CENTRAL CARBON COUNTY WY-NORTH SNOWY RANGE FOOTHILLS WY-SIERRA MADRE RANGE WY-SNOWY RANGE WY-UPPER NORTH PLATTE RIVER BASIN WY- 510 PM MDT MON AUG 15 2011 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL CARBON COUNTY UNTIL 545 PM MDT... AT 507 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING AN AREA OF SHOWERS AND THUNDERSTORMS 10 MILES SOUTHEAST OF TETON RESERVOIR...OR 21 MILES SOUTH OF RAWLINS...MOVING EAST AT 30 MPH. THIS AREA OF SHOWERS AND THUNDERSTORMS HAS A HISTORY OF PRODUCING WIND GUSTS IN EXCESS OF 50 MPH. LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE... SINCLAIR... ENCAMPMENT... SARATOGA... RYAN PARK... HANNA... THIS INCLUDES INTERSTATE 80 IN WYOMING BETWEEN MILE MARKERS 217 AND 255. THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS... FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. && LAT...LON 4197 10644 4121 10647 4117 10736 4173 10740 TIME...MOT...LOC 2309Z 255DEG 29KT 4149 10713 HAHN
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
519 PM MDT MON AUG 15 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0443 PM TSTM WND GST 9 E DAD 41.31N 107.59W
08/15/2011 M48 MPH CARBON WY PARK/FOREST SRVC
THIS IS A CORRECTION IN LOCATION FROM THE PREVIOUS STORM
REPORT.
&&
MWEILANDSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 545 PM MDT MON AUG 15 2011 WYZ103>105-109-110-114-115-160030- CENTRAL CARBON COUNTY WY-FERRIS/SEMINOE/SHIRLEY MOUNTAINS WY-LARAMIE VALLEY WY-NORTH LARAMIE RANGE WY-NORTH SNOWY RANGE FOOTHILLS WY-SHIRLEY BASIN WY-SNOWY RANGE WY- 545 PM MDT MON AUG 15 2011 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL ALBANY AND EASTERN CARBON COUNTIES UNTIL 630 PM MDT... AT 541 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING AN AREA OF SHOWERS AND THUNDERSTORMS 6 MILES NORTH OF ELK MOUNTAIN...OR 40 MILES EAST OF RAWLINS...MOVING EAST AT 30 MPH. THIS AREA OF SHOWERS AND THUNDERSTORMS HAS A HISTORY OF PRODUCING WIND GUSTS IN EXCESS OF 50 MPH. LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE... ARLINGTON... MEDICINE BOW... ROCK RIVER... THIS INCLUDES INTERSTATE 80 IN WYOMING BETWEEN MILE MARKERS 248 AND 282. THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. && LAT...LON 4224 10582 4147 10579 4163 10660 4204 10659 TIME...MOT...LOC 2345Z 268DEG 22KT 4178 10641 HAHN
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
615 PM MDT MON AUG 15 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0536 PM TSTM WND GST 20 N SARATOGA 41.74N 106.81W
08/15/2011 M50 MPH CARBON WY DEPT OF HIGHWAYS
&&
HAHNSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 633 PM MDT MON AUG 15 2011 WYZ103-105-106-110-115-116-160115- CENTRAL LARAMIE RANGE AND SOUTHWEST PLATTE COUNTY WY-LARAMIE VALLEY WY-NORTH LARAMIE RANGE WY-NORTH SNOWY RANGE FOOTHILLS WY-SHIRLEY BASIN WY-SOUTH LARAMIE RANGE WY- 633 PM MDT MON AUG 15 2011 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL ALBANY AND EASTERN CARBON COUNTIES UNTIL 715 PM MDT... AT 627 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING AN AREA OF SHOWERS AND THUNDERSTORMS 8 MILES SOUTHEAST OF MEDICINE BOW...OR 44 MILES NORTHWEST OF LARAMIE...MOVING EAST AT 30 MPH. THIS AREA OF SHOWERS AND THUNDERSTORMS HAS A HISTORY OF PRODUCING WIND GUSTS OF UP TO 55 MPH. LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE... BOSLER... GARRETT... BALDY PEAK... SYBILLE RESEARCH UNIT... && LAT...LON 4227 10532 4152 10533 4161 10619 4202 10624 TIME...MOT...LOC 0032Z 261DEG 28KT 4185 10600 HAHN
The Cheyenne radar (KCYS), 182 km away, was scanning. The volume nearest the first event began at 01:56 UTC.
2 thunderstorm wind. Local standard time, as filed.
WYDOT sensor at Walcott Junction east of Sinclair measured wind gusts of 63 mph.
WYDOT sensor at Mile Marker 249 measured wind gusts of 62 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, August 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: 324087, 324088.