A lone severe thunderstorm brought large hail and heavy rain to portions of northern Hot Springs and western Washakie counties.
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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 RIW wrote it up.
A lone severe thunderstorm brought large hail and heavy rain to portions of northern Hot Springs and western Washakie counties.
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 Aug 6, 2:28 PM MST, 42 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 328 PM MDT MON AUG 6 2007 .SHORT TERM...TONIGHT THROUGH THURSDAY STRONG THUNDERSTORMS FIRING FROM THE TETONS SOUTHEAST TO EASTERN FREMONT COUNTY ATTM. EARLIER AN INTENSE STORM BROUGHT AN ESTIMATED 1 TO 1.25 INCHES OF RAIN SOUTHEAST OF HOLE IN THE WALL ALONG WITH MARBLE SIZED HAIL. LAPS ANALYSIS INDICATES SOME SIGNIFICANT CAPE IN AREAS WITH AT LEAST MODERATE CAPE IN MOST AREAS. THERE WAS STILL SOME CIN TO OVERCOME ACROSS THE BIG HORN BASIN AND WIND RIVER BASIN. SOME OF THESE STORMS ARE PRODUCING VERY HEAVY RAINFALL RATES IN EXCESS OF 2 TO 3 INCHES PER HOUR. IN GENERAL THE STORMS ARE MOVING BUT WE WILL NEED TO WATCH FOR ANCHORED STORMS INTO THE EVENING ALONG A FEW SURFACE BOUNDARIES. THE JET STREAK MAY ALSO ASSIST SOME OF THESE STORMS OVER THE SERN ZONES INTO THE EARLY EVENING HOURS. THE AIRMASS IS EXPECTED TO DRY OUT SOME ON TUESDAY BUT THE PACNW SHORTWAVE WILL APPROACH AND PROVIDE SOME DYNAMICS TO THE NORTHWEST PART OF THE FORECAST AREA FOR A POSSIBLE ENHANCED AREA OF CONVECTION. THE AIRMASS IS FORECAST TO DRY OUT WEDNESDAY AND THURSDAY WITH MAINLY ISOLATED MOUNTAIN CONVECTION EACH DAY. LONG TERM...THURSDAY NIGHT THROUGH MONDAY SOUTHWEST FLOW ALOFT PREVAILS THURSDAY THROUGH SUNDAY WITH SHORTWAVES MOVING THROUGH THE FLOW. THE CENTER OF THE UPPER HIGH GRADUALLY SHIFTS WESTWARD TO COLORADO BY SUNDAY. MONSOON MOISTURE WILL MOST LIKELY CREEP ITS WAY BACK INTO OUR AREA AS THE HIGH CENTER SHIFTS TOWARD THE ROCKIES. HARD TO PINPOINT EXACT DAY...BUT IT APPEARS FRIDAY WILL SEE SOME INCREASE WITH A BETTER INFLUX SAT AND SUN. HAVE ADJUSTED PRECIP CHANCES TO REFLECT THIS THINKING. NEXT MONDAY LOOKS ABOUT THE SAME AS THE UPPER HIGH SHIFTS TO THE FOUR CORNERS. AS FOR TEMPS...80S AND 90S TO PREVAIL THROUGH THE PERIOD WITH 60S AND 70S IN THE MTS. AVIATION... WDLY SCT THUNDERSTORMS THROUGH THIS EVENING...WITH SOME PRODUCING VERY HEAVY RAIN AND SMALL HAIL AND WIND GUSTS TO 40 KTS. THIS ACTIVITY IS EXPECTED TO DIMINISH AFTER 02Z...WITH THE SKY CLEARING OUT. AN APPROACHING TROUGH WILL BRING ADDITIONAL SHOWERS AND THUNDERSTORMS TUESDAY AFTERNOON. SOME SOUTHWEST BREEZES WILL ALSO PICK IN THE LATE MORNING AND AFTERNOON HOURS. FIRE WEATHER... ANOTHER ROUND OF STRONG THUNDERSTORMS ARE ALREADY FIRING FROM THE TETONS SOUTHEAST TO THE WIND RIVER MOUNTAINS AND OVER INTO EASTERN FREMONT...NATRONA AND SOUTHERN JOHNSON COUNTIES. OTHER STORMS WILL FORM ACROSS THE DISTRICT INTO THE EVENING HOURS. SOME OF THESE STORMS WILL PRODUCE HEAVY RAIN... ONE HALF INCH HAIL...GUSTY WIND OF 40 TO 50 MPH AND FREQUENT LIGHTNING. ON TUESDAY...A WEATHER DISTURBANCE WILL IMPACT NORTHWEST WYOMING WHILE SOME LINGERING MOISTURE REMAINS ACROSS THE AREA. ISOLATED THUNDERSTORMS WILL FORM ONCE AGAIN ACROSS THE AREA BUT MAY BE A LITTLE MORE SCATTERED IN THE NORTHWEST MOUNTAINS. IT WILL BE DRIER STILL ON WEDNESDAY AND THURSDAY WITH ONLY ISOLATED THUNDERSTORMS IN THE HIGHER ELEVATIONS. MIN RHS WILL LOWER OVER THE NEXT COUPLE DAYS WITH SOME SOUTHWEST BREEZES IN THE AFTERNOON...ESPECIALLY IN THE MOUNTAINS AND SWEETWATER COUNTY INTO NATRONA COUNTY. RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...SKRBAC LONG TERM...AR AVIATION...TWB FIRE WEATHER...SKRBAC
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 930 AM MDT MON AUG 6 2007 WYZ001>020-022>030-071100- 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- 930 AM MDT MON AUG 6 2007 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT SCATTERED LATE AFTERNOON AND EVENING THUNDERSTORMS WILL DEVELOP ACROSS CENTRAL WYOMING TODAY. A FEW OF THESE STORMS MAY PRODUCE HEAVY RAIN...WIND GUSTS AROUND 50 MPH...SMALL HAIL AND DANGEROUS LIGHTNING. THE HIGHEST LIKELIHOOD FOR A FEW STRONGER STORMS WILL BE FROM EASTERN SWEETWATER COUNTY NORTHEAST INTO EASTERN FREMONT AND NATRONA COUNTY. HOWEVER...A FEW STRONGER STORMS ARE ALSO POSSIBLE ALONG THE SOUTHEAST SLOPE OF THE ABSAROKA MOUNTAINS AND ADJACENT LOWER ELEVATIONS AND ALSO ALONG THE EAST SLOPE OF THE BIG HORN MOUNTAINS AND ONTO THE ADJACENT LOWER ELEVATIONS OF JOHNSON COUNTY. ELSEWHERE...ISOLATED GUSTY THUNDERSTORMS ARE EXPECTED WITH THE POTENTIAL FOR 50 MPH WIND GUSTS AND DANGEROUS LIGHTNING. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY ISOLATED THUNDERSTORMS WILL OCCUR EVERY AFTERNOON AND EVENING OVER THE REGION. AN INCREASE IN MONSOONAL MOISTURE IS QUITE POSSIBLE LATE IN THE WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ASKED TO REPORT ANY WIND GUSTS OVER 40 MPH...HAIL AND HEAVY RAINFALL...OR FLOODING...THIS AFTERNOON AND TONIGHT. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 240 PM MDT MON AUG 6 2007 WYZ011-020-062130- NATRONA COUNTY LOWER ELEVATIONS-SOUTHEAST JOHNSON COUNTY- 240 PM MDT MON AUG 6 2007 ...STRONG THUNDERSTORM ALONG THE JOHNSON NATRONA COUNTY LINE... AT 226 PM...A STRONG THUNDERSTORM PRODUCING VERY HEAVY RAIN AND HALF INCH HAIL WAS LOCATED ALONG THE JOHNSON NATRONA COUNTY LINE... 10 MILES WEST OF I 25. RUNOFF FROM THIS STORM WILL AFFECT AREAS ALONG TRIPLE T RANCH ROAD...ALSO KNOWN AS LONE BEAR ROAD. RADAR ESTIMATES OF UP TO ONE AND ONE HALF INCHES HAS FALLEN. THE STORM WILL BEGIN PICKING UP SPEED AS IT HEADS OFF TO THE EAST THROUGH 330 PM. TWB
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 328 PM MDT MON AUG 6 2007 WYZ005-007-062230- OWL CREEK AND BRIDGER MOUNTAINS-SOUTHWEST BIG HORN BASIN- 328 PM MDT MON AUG 6 2007 ...STRONG THUNDERSTORMS OVER WESTERN HOT SPRINGS COUNTY... AT 320 PM...STRONG THUNDERSTORMS PRODUCING VERY HEAVY RAIN AND HALF INCH HAIL WERE LOCATED OVER WESTERN HOT SPRINGS COUNTY... IN THE VICINITY OF GRASS CREEK. THE STORMS WILL CROSS HIGHWAY 120 AFTER 330 PM...CAUSING PONDING OF WATER AND POSSIBLY HAIL ON THE ROAD SURFACE. RADAR ESTIMATES OF BETWEEN ONE AND ONE AND ONE HALF INCHES HAS FALLEN. THE STORMS ARE MOVING TO THE NORTHEAST AT 20 MPH. TWB
The Riverton/Lander radar (KRIW), 94 km away, was scanning. The volume nearest the first event began at 22:10 UTC.
3 hail, 1 flash flood. Local standard time, as filed.
Golf ball sized hail fell to the north of Little Cottonwood Creek in northern Hot Springs County.
Golf ball sized hail fell at two ranches along Little Cottonwood Creek.
Heavy rain caused mud, rocks, and water to spread from higher terrain south across Little Cottonwood Creek Road. At least one culvert and part of the road were to be replaced following the flash flood. The basement of one ranch house about six miles west of Winchester was inundated by the flood waters and mud.
Hail of 1.25 to 1.50 inches fell in Winchester.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2007Every state in 2007This day in weather historyWarnings in Wyoming, August 2007
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: 45231, 45235, 45250, 45256.