Outflow winds from collapsing showers exceeded 58 mph over portions of southeast Wyoming.
Every event with a place to put it; 3 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.
Outflow winds from collapsing showers exceeded 58 mph 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 Aug 11, 10:32 AM MST, 3 hours 51 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 1132 AM MDT SAT AUG 11 2012 .AVIATION...18Z TAF ISSUANCE... SFC FRONT NOW MOVING EAST OVER THE NEB PANHANDLE WILL BE EAST OF ALL NEB PANHANDLE TERMINALS BY 21Z WITH NW TO NORTHERLY WINDS BEHIND THIS FRONT. WDLY SCTD SHOWERS AND TSTRMS POSSIBLE MAINLY OVER EASTERN TERMINALS THIS AFTERNOON WITH BRIEF MVFR VSBYS ASSOCIATED WITH STRONGER ACTIVITY. CLEARING CONDITIONS TONIGHT. -RE- && .PREV DISCUSSION... /ISSUED 355 AM MDT SAT AUG 11 2012/ SHORT TERM...TODAY THROUGH MONDAY NIGHT... WELL DEFINED SHORTWAVE EVIDENT ON SATELLITE PIX JUST BEGINNING TO ENTER WRN MONTANA EARLY THIS MORNING. AMPLE MOISTURE OUT AHEAD OF THIS FEATURE WAS STILL PRODUCING A FEW LIGHTNING STRIKES ACROSS WRN MONTANA AS WELL AS A FEW LIGHT SHOWERS ACROSS WESTERN AND CENTRAL WYOMING. THESE SHOWERS MAY SNEAK INTO FAR WRN ZONES THROUGH SUNRISE...BUT WOULD EXPECT LITTLE MORE THAN SPRINKLES. 08Z SFC ANALYSIS SHOWS PRESSURES FALLING ALONG THE FRONT RANGE AS THE PRESSURE TROUGH SHARPENS. LLVL CONVERGENCE ALONG THIS LEE SIDE PRESSURE TROUGH ALONG WITH SPEED CONVERGENCE ASSOCIATED WITH THE LLJ EAST OF THE TROUGH WAS PRODUCING A FEW ELEVATED SHOWERS EARLY THIS AM. THESE SHOULD CONTINUE TO WEAKEN AS THEY SLIDE EAST THROUGH DAYBREAK. LATEST MODELS ARE SIMILAR IN STRENGTHENING THE H5 SHORTWAVE AS IT DIVES SE THROUGH MONTANA/WYOMING TODAY AND ONTO THE PLAINS BY THIS EVENING. 11/00Z UPSTREAM PWATS WERE RUNNING AROUND 110 TO 170 PERCENT OF NORMAL. PWATS SHOULD PEAK BETWEEN AN INCH AND AN INCH AND QUARTER EAST OF THE LARAMIE RANGE BY MIDDAY. LEE SIDE TROUGH WILL SLIDE EAST THIS MORNING WITH THE COLD FRONT PUSHING THROUGH THIS AFTERNOON. AS SUCH...EXPECT SHOWERS AND THUNDERSTORMS TO DEVELOP JUST BEFORE MIDDAY FOR AREAS ALONG AND WEST OF THE LARAMIE RANGE...THEN SPREAD EAST INTO THE PLAINS DURING THE AFTERNOON HOURS. FORECAST SOUNDINGS SUGGEST EFFICIENT RAIN PRODUCERS WITH THESE THUNDERSTORMS ONCE THEY INITIATE. HOWEVER...WITH INCREASING MID-LEVEL FLOW CONTRIBUTING TO 0-6KM BULK SHEAR OF 30 TO 40 KNOTS AND SBCAPES OF 700 TO 1000 J/KG...CANT RULE OUT SMALL HAIL AND GUSTY WIND POTENTIAL MAINLY IN THE WESTERN NEBRASKA PANHANDLE. HAVE BOOSTED PRECIPITATION CHANCES TO SCATTERED MOST PLACES AND INCLUDED SMALL HAIL/GUSTY WIND WORDING OUT EAST. SUBSIDENCE AND A DRIER AIR MASS WILL BE USHERED INTO THE AREA BEHIND THE SHORTWAVE FROM WEST TO EAST BY EARLY EVENING. SO EXPECT AND EARLY END TO CONVECTIVE CHANCES ACROSS THE CWFA. HEIGHTS WILL BUILD SLIGHTLY FOR SUNDAY AND MONDAY AS NORTHWEST FLOW PERSISTS. KEPT THINGS MOSTLY DRY FOR NOW...BUT DID BRING THUNDERSTORM CHANCES BACK IN OVER THE MOUNTAINS MONDAY AFTERNOON AND TO WRN NEBRASKA MONDAY EVENING AS MORE MOISTURE STREAMS OVER THE AREA. ANOTHER WARM DAY AHEAD OF THE FRONTAL PASSAGE TODAY WITH AFTERNOON HIGHS THAT WILL CLIMB INTO THE 80S OVER SE WYOMING AND THE 90S ACROSS THE PANHANDLE. TEMPERATURES WILL COOL 2 TO 5 DEGREES ON SUNDAY...BUT BOUNCE BACK TOWARDS THE 90S AGAIN OUT ON THE EASTERN PLAINS BY MONDAY. LONG TERM...TUESDAY THROUGH SATURDAY...00Z MODELS ARE IN FAIR AGREEMENT WITH THE LONG TERM PERIOD...WITH A SHORTWAVE DROPPING SOUTHEAST INTO THE NORTHERN PLAINS FROM CANADA MIDWEEK. AS THE WAVE APPROACHES...THE LEESIDE SFC PRESSURE TROUGH WILL DEEPEN BRINGING GUSTY WESTERLY WINDS TO AREAS WEST OF THE LARAMIE RANGE THROUGH THE DAY. TEMPS WILL REMAIN QUITE WARM DUE TO THE THERMAL RIDGE REMAINING OVERHEAD AND WITH WESTERLY WINDS IN PLACE. COULD SEE SOME WEAK MOUNTAIN CONVECTION DEVELOP AS WELL DUE TO THE APPROACHING WAVE AND WESTERLY UPSLOPE FLOW. A COLD FRONT ASSOCIATED WITH THE MAIN SHORTWAVE WILL DROP SOUTH ACROSS THE FORECAST AREA WEDNESDAY MORNING...WITH MODELS SHOWING A GOOD BATCH OF MOISTURE WITH THE UPPER LEVEL WAVE. A RATHER STRONG SURFACE HIGH LOOKS TO FOLLOW IN THE WAKE OF THE FRONT...WITH WINDS BECOMING NORTH-NORTHEAST AND COULD BE QUITE GUSTY AT TIMES. EXPECTING A FEW SHOWERS AND STORMS TO DEVELOP WITH THE FRONT...BECOMING SCATTERED THROUGH THE AFTERNOON AS UPSLOPE FLOW DEEPENS AND MIDLEVEL MOISTURE ADVECTS IN FROM THE NORTH. COULD BE MODERATE TO LOCALLY HEAVY RAINFALL AT TIMES WITH THESE STORMS THROUGH EARLY THURSDAY MORNING. WILL SEE MUCH COOLER TEMPS FOR THURSDAY ALONG WITH A FEW LINGERING SHOWERS AS UPSLOPE FLOW REMAINS IN PLACE. FRIDAY AND SATURDAY WILL SEE AN INCREASE IN TEMPS AS THE RIDGE BEGINS TO BUILD BACK OVER THE GREAT BASIN...WITH RELATIVELY LIGHT WINDS AND MOSTLY DRY CONDITIONS EXPECTED THROUGH THIS TIME. FIRE WEATHER...AN UPPER LEVEL SYSTEM WILL DRAG A COLD FRONT THROUGH THE DISTRICT THIS AFTERNOON. AHEAD OF THIS FRONT EXPECT WARM AND BREEZY CONDITIONS ACROSS THE AREA. HOWEVER...WITH INCREASED MOISTURE VALUES EXPECT MINIMUM RELATIVE HUMIDITIES TO ONLY DIP GENERALLY INTO THE UPPER TEENS AND LOW 20S. AREAS JUST EAST OF THE LARAMIE RANGE AND ACROSS FAR WESTERN CARBON COUNTY MAY SEE SLIGHTLY LOWER HUMIDITIES THROUGH THE DAY. WIND GUSTS OF 25 TO 35 MPH CAN BE EXPECTED AHEAD OF AND BEHIND THE COLD FRONTAL PASSAGE. SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP BY LATE MORNING OR MIDDAY FOR AREAS ALONG AND WEST OF THE LARAMIE RANGE AND WILL SPREAD EAST ONTO THE PLAINS DURING THE AFTERNOON. MOST OF THESE THUNDERSTORMS ARE ANTICIPATED TO PRODUCE WETTING RAINS. SHOWERS AND THUNDERSTORMS WILL DISSIPATE QUICKLY FROM WEST TO EAST LATE THIS AFTERNOON/EARLY THIS EVENING GIVING WAY TO CLEARING AND COOL CONDITIONS OVERNIGHT. A SLIGHTLY COOLER AND DRY DAY CAN BE EXPECTED ON SUNDAY. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && SHORT TERM/FIRE WEATHER...HAHN LONG TERM...RJM
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE CHEYENNE WY 115 PM MDT SAT AUG 11 2012 WYZ101>119-121730- 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- 1127 AM MDT SAT AUG 11 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL WYOMING... SOUTH CENTRAL WYOMING AND SOUTHEAST WYOMING. .DAY ONE...THIS AFTERNOON AND TONIGHT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP AND MOVE WEST TO EAST THIS AFTERNOON AS A COLD FRONT AND UPPER LEVEL WEATHER DISTURBANCE PASS THROUGH THE REGION. NONE OF THE THUNDERSTORMS ARE EXPECTED TO PRODUCE SEVERE WEATHER. GUSTY NORTHWEST WINDS OF 25 TO 35 MPH WILL OCCUR IN THE WAKE OF THE FRONTAL PASSAGE...WITH GUSTS OF 40 TO 50 MPH IN AND NEAR SOME OF THE SHOWERS AND THUNDERSTORMS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY WIDELY SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL DEVELOP MONDAY AND TUESDAY. A COLD FRONT DROPPING SOUTH THROUGH THE AREA ON WEDNESDAY WILL BRING SCATTERED SHOWERS AND THUNDERSTORMS WEDNESDAY AND THURSDAY. NONE OF THE THUNDERSTORMS ARE EXPECTED TO PRODUCE SEVERE WEATHER BUT GUSTY WINDS AT TIMES. .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>021-054-055-095-096-121730- DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-CHEYENNE- NORTH SIOUX-SOUTH SIOUX- 115 PM MDT SAT AUG 11 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA PANHANDLE. .DAY ONE...THIS AFTERNOON AND TONIGHT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP DURING THE AFTERNOON AND LINGER INTO THE EARLY EVENING HOURS AS A COLD FRONT AND UPPER LEVEL WEATHER DISTURBANCE MOVE THROUGH THE REGION. GUSTY NORTHWEST WINDS OF 25 TO 35 MPH WILL OCCUR IN THE WAKE OF THE FRONTAL PASSAGE. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY WIDELY SCATTERED MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL DEVELOP WEDNESDAY AND THURSDAY. NONE OF THE STORMS ARE EXPECTED TO PRODUCE SEVERE WEATHER BUT GUSTY WINDS AT TIMES. .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 JAMSKI
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 135 PM MDT SAT AUG 11 2012 WYZ104-109-110-112015- CENTRAL CARBON COUNTY WY-FERRIS/SEMINOE/SHIRLEY MOUNTAINS WY-NORTH SNOWY RANGE FOOTHILLS WY- 135 PM MDT SAT AUG 11 2012 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL CARBON COUNTY UNTIL 215 PM MDT... AT 124 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 6 MILES NORTH OF SEPARATION LAKE...OR 20 MILES NORTH OF RAWLINS...MOVING EAST-SOUTHEAST AT 30 MPH. PEA SIZE HAIL AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM. THIS STORM WILL BE NEAR... RURAL CENTRAL CARBON COUNTY THROUGH 215 PM MDT IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. && LAT...LON 4208 10659 4177 10677 4200 10730 4218 10721 TIME...MOT...LOC 1935Z 292DEG 25KT 4204 10714 JAMSKI
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 206 PM MDT SAT AUG 11 2012 WYZ101-103-112100- CONVERSE COUNTY LOWER ELEVATIONS WY-NORTH LARAMIE RANGE WY- 206 PM MDT SAT AUG 11 2012 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN CONVERSE COUNTY UNTIL 300 PM MDT... AT 204 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 8 MILES SOUTHWEST OF GLENROCK...OR 17 MILES SOUTHEAST OF EVANSVILLE...MOVING EAST AT 30 MPH. HAIL UP TO THE SIZE OF PENNIES AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH FREQUENT DANGEROUS LIGHTNING. LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE... DOUGLAS... ROLLING HILLS ESTATES... GLENROCK... DEER CREEK... BOXELDER... LAPRELE RESERVOIR... THIS INCLUDES INTERSTATE 25 IN WYOMING BETWEEN MILE MARKERS 133 AND 172. IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. && LAT...LON 4283 10526 4239 10542 4269 10605 4293 10601 TIME...MOT...LOC 2006Z 291DEG 28KT 4277 10593 CLAYCOMB
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE CHEYENNE WY 316 PM MDT SAT AUG 11 2012 WYZ107-108-112215- EAST PLATTE COUNTY WY-GOSHEN COUNTY WY- 316 PM MDT SAT AUG 11 2012 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN PLATTE AND NORTHERN GOSHEN COUNTIES UNTIL 415 PM MDT... AT 312 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR GLENDO...OR 23 MILES SOUTHEAST OF DOUGLAS... MOVING EAST AT 45 MPH. WIND GUSTS UP TO 55 MPH ARE EXPECTED WITH THIS STORM. THIS STORM WILL BE NEAR... HARTVILLE AROUND 340 PM MDT. HWY 85 AT DRY RAWHIDE CREEK AROUND 410 PM MDT. THIS INCLUDES INTERSTATE 25 IN WYOMING BETWEEN MILE MARKERS 106 AND 118. IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. && LAT...LON 4243 10415 4212 10425 4247 10518 4258 10512 TIME...MOT...LOC 2116Z 291DEG 39KT 4250 10503 RUBIN
The national radar mosaic for the moment the first event began.
3 high wind. Local standard time, as filed.
A spotter 18 miles west-northwest of Cheyenne reported a peak wind gust of 72 mph.
The wind sensor at the Skyline observation site (elevation 8097 feet) measured a peak gust of 58 mph.
The UPR sensor near Buford (elevation 7979 feet) measured a peak wind gust of 61 mph.
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, August 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: 395564, 395565, 395566.