Surface dew points approaching 60F combined with a weak upper level disturbance to generate a lone late evening thunderstorm over northern Johnson County. Storm intensity increased rapidly as the cell moved east off the Bighorn Mountains onto the plains near Buffalo.
Every event with a place to put it. 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 RIW wrote it up.
Surface dew points approaching 60F combined with a weak upper level disturbance to generate a lone late evening thunderstorm over northern Johnson County. Storm intensity increased rapidly as the cell moved east off the Bighorn Mountains onto the plains near Buffalo. The storm continued to strengthen over northeast Johnson County producing a swath of one inch diameter or larger hail across 10 miles or more.
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 23, 1:07 PM MST, 8 hours 5 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 207 PM MDT TUE JUN 23 2015 .SHORT TERM...TONIGHT THROUGH WEDNESDAY WV IMAGERY SHOWS FLAT RIDGING OVR THE WEST...WITH A COUPLE OF EMBEDDED SWS MOVING THRU THE FLOW...ONE OVR NRN WY...ANOTHER JUST UPSTREAM WITH AXIS STRETCHING FROM ERN WA TO ERN OR. SFC HAS WEAK LOW P BUILDING ACROSS SRN WY...HIGH P WELL OFF TO THE E OVR THE PLAINS WITH A BOUNDARY/WEAK FRONT IN BETWEEN FROM NRN WY TO SERN WY. VERY WARM TO HOT UNDER MODEST TO FLAT RIDGING...BUT WITH RISING HEIGHTS. SMALL/LEADING SW CURRENTLY MOVING ACROSS THE NW FA. NRN MOUNTAINS AND DEVELOPING LOW AND ATTENDANT BOUNDARY (WARM)FRONT WILL BE AREA TO FOCUS ON FOR CI LATER TODAY/TONIGHT. EXPECT ONLY ISOLATED STORMS AT BEST WITH FAIRLY WIDESPREAD CAPPING IN PLACE...WIDELY SCATTERED TO THE E AND NE OF THE FA. WITH ML CAPE IN THE 1500 TO 2000 J/KG RANGE AND EFFECTIVE SHEAR OF 40 TO 50 KTS...ESPECIALLY NEAR THE LL RETURN FLOW (ERLY/NERLY) AROUND THE NWD MOVING FRONT IN JOHNSON COUNTY. GENTLE CLOCKWISE HODOGRAPH WILL GIVE SLIGHT PREFERENCE TO RIGHT MOVERS TODAY. IF A STORM DOES GO UP IT COULD BE STRONG WITH HAIL TO .75 INCH AND STRONG WIND GUSTS APPROACHING SEVERE BEFORE IT MOVES OUT OF THE CWA TO THE EAST. WHILE STORMS WILL BE ROTATING WELL ENOUGH...TORNADO THREAT SEEM RELATIVELY LOW WITH RELATIVELY SMALL LL SHEAR AND LCLS ON THE HIGH SIDE. THE SECOND (UPSTREAM) SW WILL THEN MOVE ACROSS THE CWA LATER TONIGHT...HELPING TO DEVELOP AND EVENTUALLY PUSH FRONT BACK SWD ON WED. BEFORE THAT HOWEVER...MID LVL FRONT DEVELOPMENT WITH LL JET TO THE SOUTH WILL BE THE LIKELY LOCATION FOR MCS FORMATION LATE TONIGHT/THRU WED MORNING...MAINLY EAST OF THE FA. WED...SIMILAR SET-UP TO THAT OF TODAY BY LATE IN THE AFTERNOON/EVENING WITH A LITTLE BETTER SFC TO MID LVL FORCING N OF THE FRONT INTO JOHNSON COUNTY...MAKING IT SLIGHTLY EASIER FOR CI TO OCCUR AND ISOLATED TO WIDELY SCATTERED STORMS TO FORM ACROSS NRN JOHNSON...FROM THE BIGHORNS EWD TO THE BORDER. ATTM...BEST AREA FOR STRONG/SEVERE STORMS LOOKS TO LAY ON OR JUST E OF THE JOHNSON COUNTY BORDER. WINDS BACKING FROM SFC TO ALOFT AND SLIGHT CLOCKWISE TO STRIGHTLINE HODOGRAPHS WILL GIVE LARGELY MIXED MODE CONVECTION WITH SPLITTING STORMS A POSSIBILITY...ALONG WITH NEAR SEVERE HAIL/WINDS FOR A SHORT PERIOD. .LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY THE CONVECTION OF WEDNESDAY AFTERNOON SHOULD LINGER INTO THE EVENING...ESPECIALLY ACROSS EASTERN PORTIONS OF THE COUNTY WARNING AREA. MODELS ARE EVEN SHOWING IT LINGER INTO THE LATE WEDNESDAY NIGHT HOURS WITH THE POSSIBLE DEVELOPMENT OF AN MCS IN PORTIONS OF NATRONA AND ESPECIALLY JOHNSON COUNTY. AS A RESULT...WE INCREASED POPS A BIT IN THAT AREA. AS FOR THURSDAY...WITH THE BOUNDARY REMAINING IN THE AREA WE MAINTAINED THE CHANCE OF THUNDERSTORMS...ONCE AGAIN THE BEST CHANCE IN EASTERN AREAS WHERE THE BEST CAPE AND CONVERGENCE WILL BE. WITH MORE CLOUD COVER WE ALSO LOWERED TEMPERATURES A COUPLE OF DEGREES...ALTHOUGH IT WILL STILL BE A VERY WARM DAY. FOLLOWING THAT...WE LOOK TO ENTER A WASH...RINSE...REPEAT CYCLE. THE REASON IS A STRONG RIDGE OF HIGH PRESSURE...A BOILER PLATE RIDGE AS ONE OF MY FORMER COLLEAGUES USED TO CALL IT...BUILDS ACROSS THE NORTHERN ROCKIES. THAT MEANS A PATTERN OF HOT TEMPERATURES FOR MOST LOCATIONS...90S WILL BE COMMONPLACE STARTING THIS WEEKEND AND ESPECIALLY EARLY NEXT WEEK WHEN THE HEAT IS EXPECTED TO PEAK. THE WARMER LOCATIONS IN THE BIG HORN BASIN SUCH AS GREYBULL AND WORLAND COULD EVEN SEE THE DREADED TRIPLE DIGITS FOR HIGH TEMPERATURES EARLY NEXT WEEK. AS FOR ANY CHANCE OF CONVECTION...WITH THE HIGH HEIGHTS FROM THE STRONG RIDGE THUNDERSTORMS ARE EXPECTED TO BE FEW AND FAR BETWEEN. ANY THAT DO DEVELOP WOULD BE OF THE HIGH ELEVATION HEAT SOURCE VARIETY ACROSS THE MOUNTAINS. BUT EVEN HERE...WITH LIMITED MOISTURE COVERAGE SHOULD BE FAIRLY SPARSE. AND...WITH MAINLY LIGHT STEERING FLOW EXPECTED...THE CHANCE ANY COULD DRIFT INTO THE LOWER ELEVATIONS OTHER THAN MAYBE THE ADJACENT FOOTHILLS LOOKS SLIM TO NONE AT THIS TIME. && .AVIATION.../00Z ISSUANCE/ VFR CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD. AN ISOLATED THUNDERSTORM OR TWO WILL BE POSSIBLE ACROSS FAR NORTHERN WY AND OVR NORTHERN JOHNSON COUNTY...INCLUDING VCNTY KCOD AND KBYG THIS EVENING. DRY THROUGH THE REST OF OF THE FORECAST. GUSTY WEST TO SOUTHWEST WINDS THROUGH 03Z SOUTH OF AND VCNTY KLND TO KCPR LINE. && .FIRE WEATHER... FIRE DANGER WILL REMAIN BELOW CRITICAL FOR ANOTHER DAY OR SO AS THE AREA REMAINS IN GREEN-UP. HOWEVER...FIRE DANGER WILL BE ENHANCED BOTH TODAY AND TOMORROW ACROSS THE SOUTHERN HALF OF THE FORECAST AREA AS HOT DAY TIME TEMPERATURES CONTINUE WITH MINIMUM RH VALUES IN THE LOWER TEENS...COMBINING WITH WINDS OCCASIONALLY GUSTING TO AROUND 25 MPH THROUGH EARLY EVENINGS. NO PRECIPITATION EXPECTED ACROSS MOST OF THE FORECAST AREA EXCEPT FOR SMALL CHANCES OVR THE FAR NORTHERN AND NORTHEASTERN ZONES WHERE ISOLATED TO WIDELY SCATTERED STORMS WILL BE POSSIBLE. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...BRAUN LONG TERM...HATTINGS AVIATION...BRAUN FIRE WEATHER...BRAUN
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 431 AM MDT TUE JUN 23 2015 WYZ001>020-022>030-241045- YELLOWSTONE NATIONAL PARK-ABSAROKA MOUNTAINS-CODY FOOTHILLS- NORTH BIG HORN BASIN-SOUTHWEST BIG HORN BASIN- SOUTHEAST BIG HORN BASIN-OWL CREEK AND BRIDGER MOUNTAINS- BIGHORN MOUNTAINS WEST-BIGHORN MOUNTAINS SOUTHEAST- NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY- TETON AND GROS VENTRE MOUNTAINS-JACKSON HOLE- WIND RIVER MOUNTAINS WEST-WIND RIVER MOUNTAINS EAST- UPPER WIND RIVER BASIN-WIND RIVER BASIN-LANDER FOOTHILLS- GREEN MOUNTAINS AND RATTLESNAKE RANGE- NATRONA COUNTY LOWER ELEVATIONS-CASPER MOUNTAIN-STAR VALLEY- SALT RIVER AND WYOMING RANGES-UPPER GREEN RIVER BASIN FOOTHILLS- UPPER GREEN RIVER BASIN-SOUTH LINCOLN COUNTY- ROCK SPRINGS AND GREEN RIVER-FLAMING GORGE-EAST SWEETWATER COUNTY- 431 AM MDT TUE JUN 23 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WY...CENTRAL WYOMING...NORTH CENTRAL WYOMING...NORTHWEST WYOMING...SOUTH CENTRAL WYOMING AND WEST CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT ISOLATED THUNDERSTORMS IN FAR NORTHERN WYOMING THIS AFTERNOON AND EVENING. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WEDNESDAY...ISOLATED THUNDERSTORMS IN FAR NORTHERN WYOMING IN THE AFTERNOON AND EVENING. THURSDAY...A BETTER CHANCE OF SHOWERS AND LATE DAY THUNDERSTORMS EAST OF THE DIVIDE. SATURDAY THROUGH TUESDAY...A FEW LATE DAY MOUNTAIN THUNDERSTORMS POSSIBLE...OTHERWISE DRY AND VERY WARM TO HOT. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
952 PM MDT TUE JUN 23 2015
WYZ010-240430-
NORTHEAST JOHNSON COUNTY-
952 PM MDT TUE JUN 23 2015
AT 947 PM MDT...DOPPLER RADAR WAS TRACKING A THUNDERSTORM JUST
NORTH OF BUFFALO...MOVING EAST NORTHEAST AT 30 MPH.
THIS STORM WILL REMAIN OVER MAINLY RURAL AREAS OF NORTHEASTERN
JOHNSON COUNTY...AND IMPACT INTERSTATE 90 BETWEEN MILE MARKERS 49
AND 60. THE MAIN HAZARD FROM THIS STORM WILL BE BRIEF HEAVY
RAINFALL.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
HEAVY RAINFALL OCCURRING WITH THIS STORM...MAY LEAD TO MINOR
FLOODING IN LOW LYING OR POOR DRAINAGE AREAS. DO NOT DRIVE YOUR
VEHICLE THROUGH FLOODED ROADWAYS.
&&
LAT...LON 4433 10650 4434 10662 4432 10673 4430 10676
4433 10678 4446 10683 4456 10647 4456 10616
4433 10616
TIME...MOT...LOC 0347Z 254DEG 26KT 4440 10669
21The Riverton/Lander radar (KRIW), 213 km away, was scanning. The volume nearest the first event began at 04:13 UTC.
2 hail. Local standard time, as filed.
Golf ball sized hail fell at a ranch along Tipperary Road east of Buffalo. The hail broke one window at a home on the ranch.
One inch diameter hail fell at a ranch in rural Johnson County north of Interstate 90. The hail was part of an at least 10 mile swath of large hail that moved east across the county.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2015Every state in 2015This day in weather historyWarnings in Wyoming, June 2015
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: 575576, 591483.