A developing low pressure system helped to initiate severe thunderstorms over Natrona County during the early evening hours of June 8. The largest hail reported was two inches in diameter north of Bar Nunn.
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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 developing low pressure system helped to initiate severe thunderstorms over Natrona County during the early evening hours of June 8. The largest hail reported was two inches in diameter north of Bar Nunn.
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 Jun 8, 2:55 PM MST, 3 hours 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 355 PM MDT WED JUN 8 2011 SHORT TERM...TONIGHT THROUGH SATURDAY ACTIVE AFTERNOON AS AFTERNOON HEATING IS COMBINING WITH APPROACHING TROUGH DYNAMICS AND SEVERAL JET STREAKS. STORMS WITH VERY HEAVY RAIN ARE FIRING FROM THE EAST SLOPE OF THE ABSAROKAS INTO THE WESTERN PART OF THE BIGHORN BASIN. SCATTERED THUNDERSTORMS ALSO FIRING ACROSS THE WEST WITH MORE ISOLATED COVERAGE FURTHER EAST. FFMP IS ALREADY REPORTING UP TO AN INCH IN A FEW AREAS AROUND MEETEETSE TO PITCHFORK. HAVE EXPANDED THE FLASH FLOOD WATCH TO INCLUDE THE REST OF NORTH CENTRAL WYOMING WESTWARD TO THE ABSAROKAS AND SOUTH TO DUBOIS AND THE OWL CREEKS. POTENTIAL FOR UP TO AN INCH EXISTS WITH LOCALLY HIGHER AMOUNTS THROUGH THE NIGHT. THE WIND RIVER BASIN MAY NEED TO BE ADDED LATER TO THE FLASH FLOOD WATCH AS THE TROUGH DYNAMICS SPREAD FURTHER SOUTHEAST WITH THE APPROACH OF THE NEXT JET STREAK. UPPER LOW LOOKS LIKE IT WILL TRACK RIGHT THROUGH THE WIND RIVER BASIN ON THURSDAY WITH CONSIDERABLE SHOWERS AND AT LEAST ISOLATED TO SCATTERED THUNDERSTORM COVERAGE ACROSS THE ENTIRE AREA. ENHANCEMENT EXPECTED ALONG THE TRACK OF THE MID LEVEL CIRCULATION. GRADUAL IMPROVEMENT THURSDAY NIGHT WITH A DRY DAY FRIDAY IN MOST AREAS. SOME RESIDUAL MOISTURE WILL LIKELY ALLOW FOR A FEW STORMS TO FIRE LATE IN THE DAY ACROSS THE NORTHWEST MOUNTAINS. NEXT DISTURBANCE APPROACHES SATURDAY FOR ANOTHER ROUND OF SCATTERED LATE DAY THUNDERSTORMS IN THE MOUNTAINS AND AT LEAST ISOLATED ELSEWHERE. COOL TODAY AND FRIDAY THEN RETURNING TO NEAR NORMAL TEMPERATURES SATURDAY. A COOL TO COLD START TO THE DAY FRIDAY MORNING. LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY THROUGH THE EXTENDED...MEDIUM RANGE MODELS CONTINUE TO SHOW WEAK TROUGHINESS OVER THE WEST...AND STRONG RIDGING OVER THE SOUTH CENTRAL/SOUTHEAST STATES. WEAK SHORTWAVE TROUGHS COULD PERIODICALLY IMPACT THE FORECAST AREA DURING THE EXTENDED...BUT MEDIUM RANGE MODELS ARE HAVING A DIFFICULTY IN TIMING AND LOCATION OF THESE SYSTEMS. ONE OF THESE SYSTEMS IS PROJECTED TO IMPACT THE AREA SATURDAY/SATURDAY NIGHT. THE BEST FORCING AND MOISTURE CURRENTLY IS PROGGED TO BE NORTH OF THE AREA...WITH THE BEST SHOT AT PRECIPITATION IN THE FORECAST AREA OVER THE NORTHWEST AND NORTHERN SECTIONS. THE ASSOCIATED WEAK COLD FRONT IS EXPECTED TO MOVE ACROSS LATE SATURDAY/SATURDAY NIGHT. OTHER DISTURBANCES COULD AFFECT THE AREA SUNDAY AND MONDAY. GLOBAL MODELS ARE HINTING AT A STRONGER SYSTEM SLIDING SOUTHEAST OUT OF BRITISH COLUMBIA IMPACTING THE NORTHERN ROCKIES IN THE TUESDAY THROUGH THURSDAY TIMEFRAME NEXT WEEK. HOWEVER...LARGE DISCREPANCIES EXIST THIS FAR OUT. TEMPERATURES IN THE EXTENDED ARE EXPECTED TO GENERALLY BE SLIGHTLY BELOW AVERAGE. SOME HIGHS COULD BE AS MUCH AS 15 DEGREES BELOW AVERAGE...BUT WILL NOT GO THAT COOL YET. AVIATION... SHOWERS AND THUNDERSTORMS WILL BE FOUND ACROSS MUCH OF THE FORECAST AREA THROUGH THE OVERNIGHT HOURS. STRONGER STORMS ARE POSSIBLE OVER NATRONA AND JOHNSON COUNTIES...AS WELL AS WESTERN WYOMING. STRONG AND ERRATIC WIND TO 45 KTS WILL BE POSSIBLE WITH THUNDERSTORM ACTIVITY IN THESE AREAS...AND MAY IMPACT KCPR...KJAC...KBPI AND KPNA. WEAKER WINDS WITH GUSTS UP TO 40 KTS WILL BE POSSIBLE ELSEWHERE. SMALL HAIL AND BRIEF PERIODS OF HEAVY RAINFALL WILL ALSO BE POSSIBLE WITH STORM ACTIVITY TODAY. STORM ACTIVITY MAY BRING PERIODS OF MVFR CONDITIONS. A LULL IN SHOWER ACTIVITY WILL BE FOUND OVER THE SOUTHERN HALF OF THE STATE BETWEEN 12Z AND 18Z THURSDAY...WITH WIDESPREAD SHOWERS AND THUNDERSTORMS EXPECTED AFTER 18Z. MVFR CONDITIONS WILL AGAIN BE POSSIBLE IN SHOWER AND THUNDERSTORM ENVIRONMENTS. MOUNTAIN TOPS WILL HAVE PERIODS OF BEING OBSCURED IN LOW CLOUDS...AND STRONGER TURBULENCE WILL BE FOUND IN THUNDERSTORM ENVIRONMENTS. HYDROLOGY... STRONG THUNDERSTORMS MAY LEAD TO FLASH FLOODING ACROSS MUCH OF NORTH CENTRAL WYOMING THROUGH TONIGHT WITH A FEW STRONGER STORMS EXTENDING SOUTH INTO CENTRAL WYOMING. THE THREAT OF SHOWERS AND THUNDERSTORMS WILL EXIST THROUGH THURSDAY WITH THE STRONGEST STORMS THROUGH TONIGHT. NEW RAINFALL OF ONE HALF TO INCH INCH IS POSSIBLE ACROSS THE NORTH TONIGHT WITH LOCALLY HIGHER AMOUNTS. THE CENTRAL SECTIONS MAY SEE ONE QUARTER TO ONE HALF INCH WITH LOCAL AMOUNTS UP TO AN INCH. FRIDAY WILL BE DRIER WITH A FEW LATE DAY STORMS OVER THE NORTHWEST MOUNTAINS. SCATTERED LATE DAY THUNDERSTORMS ARE EXPECTED OVER THE WEEKEND IN THE MOUNTAINS WITH ISOLATED STORMS ELSEWHERE. TEMPERATURES WILL BE COOL THROUGH FRIDAY WITH MORE SEASONABLE WEATHER OVER THE WEEKEND. && .RIW WATCHES/WARNINGS/ADVISORIES... FLASH FLOOD WATCH THROUGH LATE TONIGHT WYZ002>011-016. FLOOD WATCH THROUGH TUESDAY MORNING WYZ020. && SHORT TERM...SKRBAC LONG TERM...WM AVIATION...BRANHAM HYDROLOGY...SKRBAC
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MDT THU JUN 9 2011 WYZ001>020-022>030-091100- 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- 500 AM MDT THU JUN 9 2011 ...AREAL FLOOD WARNING ACROSS STAR VALLEY FOR THE SALT RIVER AND ITS TRIBUTARIES THROUGH THURSDAY AFTERNOON... ...FLOOD ADVISORY IN EFFECT FOR YELLOWSTONE NATIONAL PARK AND EXTREME NORTHWEST TETON COUNTY THROUGH WEDNESDAY EVENING... ...FLOOD WATCH FOR NATRONA COUNTY THROUGH NEXT TUESDAY MORNING... ...FLASH FLOOD WATCH FOR MUCH OF NORTH CENTRAL WYOMING THROUGH TONIGHT. ...SEVERE THUNDERSTORMS POSSIBLE MAINLY ACROSS NATRONA AND SOUTHERN JOHNSON COUNTIES THIS AFTERNOON AND EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT STRONG TO POTENTIALLY SEVERE THUNDERSTORMS MAY DEVELOP ACROSS NORTH CENTRAL AND CENTRAL WYOMING THROUGH TONIGHT. THE PRIMARY HAZARDS WILL BE LARGE HAIL...HEAVY RAIN...FREQUENT LIGHTNING AND POSSIBLY STRONG DAMAGING WINDS. VERY HEAVY RAIN COULD CAUSE FLASH FLOODING. THE STORMS COULD TRAIN OVER AREAS THAT HAVE ELEVATED STREAMFLOW DUE TO RECENT SNOWMELT. THUNDERSTORMS WILL ALSO OCCUR ACROSS WESTERN WYOMING IN ADVANCE OF THE NEXT STORM SYSTEM. THE THREAT OF THUNDERSTORMS WILL COVER MUCH OF CENTRAL AND WESTERN WYOMING TODAY AND THURSDAY WITH THE POTENTIAL FOR SOME LOCALIZED FLOODING CONCERNS DUE TO HEAVY RAIN ON THE RECORD SNOWPACK IN ISOLATED LOCATIONS. CREEKS AND RIVERS WILL REMAIN HIGH AND SWIFT OVER MUCH OF THE AREA. PLEASE SEE THE LATEST HYDROLOGICAL PRODUCTS FOR THE MOST CURRENT RIVER AND STREAM INFORMATION. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS WILL CONTINUE OVER THE AREA THROUGH THURSDAY NIGHT...ESPECIALLY OVER THE NORTHERN...TWO THIRDS OF THE AREA. ADDITIONAL RUNOFF FROM THIS PRECIPITATION COULD RESULT IN MORE CREEK AND RIVER RISES...AND THE POSSIBILITY OF SOME FLOODING. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 531 PM MDT WED JUN 8 2011 WYZ005-007-090015- OWL CREEK AND BRIDGER MOUNTAINS-SOUTHWEST BIG HORN BASIN- 531 PM MDT WED JUN 8 2011 AN AREA OF STRONG THUNDERSTORMS WILL MOVE NORTH OUT OF FREMONT COUNTY AND INTO HOT SPRINGS THROUGH 630 PM. THE FIRST LINE OF STORMS WILL AFFECT THE AREA ACROSS EASTERN HOT SPRINGS COUNTY FROM NEAR THERMOPOLIS AND THE WIND RIVER CANYON EASTWARD. PEA SIZE HAIL ...HEAVY RAIN...GUSTY WIND TO 45 MPH AND FREQUENT LIGHTNING CAN BE EXPECTED. TAKE SHELTER INDOORS AS THESE STORMS MOVE NORTH THROUGH THE AREA. SKRBAC
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 532 PM MDT WED JUN 8 2011 WYZ005>007-017-090015- OWL CREEK AND BRIDGER MOUNTAINS WY-SOUTHEAST BIG HORN BASIN WY-SOUTHWEST BIG HORN BASIN WY-WIND RIVER BASIN WY- 532 PM MDT WED JUN 8 2011 ...SIGNIFICANT WEATHER ADVISORY FOR WESTERN WASHAKIE...CENTRAL HOT SPRINGS AND CENTRAL FREMONT COUNTIES UNTIL 615 PM MDT... AT 530 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING AN AREA OF STRONG THUNDERSTORMS IN THE WIND RIVER CANYON MOVING NORTH AT 25 MPH. PEA SIZED HAIL AND WIND GUSTS OF 30 TO 40 MPH ARE POSSIBLE WITH THESE THUNDERSTORMS. THE HAIL MAY COVER THE GROUND IN A SHORT PERIOD OF TIME. RAINFALL OF ONE-QUARTER TO ONE-HALF INCH IS EXPECTED. THIS STORM WILL BE NEAR... THERMOPOLIS AROUND 555 PM MDT. LUCERNE AROUND 610 PM MDT. KIRBY AROUND 615 PM MDT. IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. SLOW DOWN WHEN DRIVING THROUGH AREAS WHERE HAIL COVERS THE ROAD OR WHERE PONDING OF WATER OCCURS. HIGHWAY 789 WILL BE IMPACTED BY THESE STORMS. REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN RIVERTON AT 1-800-211-1448. LAT...LON 4389 10837 4383 10788 4332 10805 4333 10841 TIME...MOT...LOC 2330Z 192DEG 23KT 4347 10819 JONES
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 551 PM MDT WED JUN 8 2011 WYZ007-009-017-019-020-090030- BIGHORN MOUNTAINS SOUTHEAST WY-GREEN MOUNTAINS AND RATTLESNAKE RANGE WY-NATRONA COUNTY LOWER ELEVATIONS WY-OWL CREEK AND BRIDGER MOUNTAINS WY-WIND RIVER BASIN WY- 551 PM MDT WED JUN 8 2011 ...SIGNIFICANT WEATHER ADVISORY FOR WESTERN NATRONA COUNTY UNTIL 630 PM MDT... AT 548 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR ERVAY...OR 18 MILES SOUTH OF HILAND...MOVING NORTHEAST AT 30 MPH. HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING. A QUICK ONE-HALF INCH OF RAIN WILL LIKELY ACCUMULATE IN ABOUT 20 TO 30 MINUTES. THIS STORM WILL BE NEAR... HIGHWAY 20/26 BETWEEN HILAND AND WALTMAN AROUND 625 PM MDT. THIS AREA INCLUDES THE WALTMAN REST AREA. IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. MOTORISTS ON HIGHWAY 20/26 SHOULD PREPARE FOR PONDING OF WATER ON THE ROADWAY ALONG WITH PEA SIZED HAIL COVERING THE ROAD IN SPOTS. REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN RIVERTON AT 1-800-211-1448. LAT...LON 4332 10751 4313 10688 4270 10731 4279 10753 TIME...MOT...LOC 2348Z 214DEG 24KT 4286 10742 JONES
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 616 PM MDT WED JUN 8 2011 WYZ005-006-090100- SOUTHEAST BIG HORN BASIN-SOUTHWEST BIG HORN BASIN- 616 PM MDT WED JUN 8 2011 AN AREA OF STRONG THUNDERSTORMS WILL CONTINUE TO MOVE NORTH ACROSS HOT SPRINGS COUNTY AND INTO WASHAKIE COUNTY THROUGH 700 PM. PEA SIZE HAIL...BRIEF HEAVY RAIN OF AROUND ONE-QUARTER INCH...AND FREQUENT LIGHTNING CAN BE EXPECTED. TAKE SHELTER INDOORS AS THESE STORMS APPROACH YOUR LOCATION. IMPACTED LOCATIONS INCLUDE KIRBY... WINCHESTER...AND COTTONWOOD CREEK. CNJ
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 652 PM MDT WED JUN 8 2011 WYZ026>028-090200- ROCK SPRINGS AND GREEN RIVER-SOUTH LINCOLN COUNTY- UPPER GREEN RIVER BASIN- 652 PM MDT WED JUN 8 2011 AN AREA OF STRONG THUNDERSTORMS WILL CONTINUE TO MOVE NORTH ACROSS THE SOUTHERN LINCOLN COUNTY...WESTERN SWEETWATER COUNTY...AND THE UPPER GREEN RIVER BASIN THROUGH 800 PM. HALF INCH HAIL...FREQUENT LIGHTNING...AND GUSTY WIND TO 40 MPH ARE POSSIBLE WITH THESE STORMS. IMPACTED LOCATIONS INCLUDE FARSON AND US HIGHWAY 101 BETWEEN EDEN AND PINEDALE AND THE FONTENELLE RESERVOIR. DSB
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 654 PM MDT WED JUN 8 2011 WYZ014-015-018-019-090145- GREEN MOUNTAINS AND RATTLESNAKE RANGE WY-LANDER FOOTHILLS WY-WIND RIVER MOUNTAINS EAST WY-WIND RIVER MOUNTAINS WEST WY- 654 PM MDT WED JUN 8 2011 ...SIGNIFICANT WEATHER ADVISORY FOR EXTREME NORTHERN SWEETWATER AND SOUTHERN FREMONT COUNTIES UNTIL 745 PM MDT... AT 650 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 9 MILES EAST OF OREGON BUTTES...OR 37 MILES SOUTH OF LANDER...MOVING NORTH AT 20 MPH. HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH FREQUENT DANGEROUS LIGHTNING. THIS STORM WILL BE NEAR... SOUTH PASS CITY AROUND 715 PM MDT. ATLANTIC CITY AROUND 725 PM MDT. STATE HWY 28 MILE MARKER 60 AROUND 745 PM MDT. IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A STURDY BUILDING. REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN RIVERTON AT 1-800-211-1448. LAT...LON 4270 10870 4258 10828 4220 10862 4226 10884 TIME...MOT...LOC 0054Z 201DEG 19KT 4232 10868 BERC
The Riverton/Lander radar (KRIW), 152 km away, was scanning. The volume nearest the first event began at 01:09 UTC.
4 hail, 1 funnel cloud. Local standard time, as filed.
Natrona County Dispatch forwarded two reports of funnel clouds west of Casper. Several other reports of cloud rotation were received.
A strong thunderstorm moved northeast across U.S. Highway 20/26 producing quarter sized hail at Natrona.
A local television meteorologist submitted a firsthand report of 1.25 inch diameter hail near the Casper/Natrona County International Airport.
An off-duty NWS employee and the public each reported two inch diameter hail on Interstate 25 at milepost 195 north of Bar Nunn.
A strong thunderstorm moved across northern Natrona County producing quarter sized hail at the Teapot Ranch.
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, June 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: 326645, 314337, 314341, 314339, 314342.