A thunderstorm formed on Casper Mountain and moved north across Casper.
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The episode as NWS RIW wrote it up.
A thunderstorm formed on Casper Mountain and moved north across Casper.
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 May 26, 3:17 AM MST, 9 hours 52 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 417 AM MDT WED MAY 26 2010 .SHORT TERM...TODAY THROUGH FRIDAY NIGHT A RIDGE OF HIGH PRESSURE IS CURRENTLY KEEPING MOSTLY CLEAR SKIES AROUND THE AREA EXCEPT ACROSS NORTHERN WY WHERE SOME MID CLOUDS LINGER. A WELL DEFINED CIRCULATION OFF THE BC COAST AT 50N/140W WILL BE EJECTING A LEAD VORT LOBE NORTHEAST ACROSS WYOMING TODAY WITHIN THE BROAD CYCLONIC CIRCULATION AROUND THIS PACIFIC LOW. THE LEADING EDGE OF A HIGH DECK OF CLOUDS ASSOCIATED WITH THIS VORT LOBE SHOULD ARRIVE IN THE CENTRAL BASINS BY 12Z THIS MORNING AND INTO THE CASPER AREA BY 15Z. A STRENGTHENING SOUTH SOUTHWEST FLOW WILL BECOME ESTABLISHED AS THE RIDGE BUILDS OVER THE GREAT PLAINS IN RESPONSE TO THE LOW TRACKING NORTH THROUGH MANITOBA AND THE AFOREMENTIONED PACIFIC LOW AND ASSOCIATED TROUGH MOVE EAST TOWARD WY. THIS SSW FLOW WILL USHER IN MUCH WARMER TEMPS. THIS VORT LOBE APPEARS THAT IT WILL GENERATE A BRIEF EPISODE OF LATE AFTERNOON THUNDERSTORMS IN OUR FAR EASTERN ZONES. THE CLOUD SHIELD WILL INHIBIT CONVECTION UNTIL THE LATE AFTERNOON HOURS. BY LATE AFTERNOON A WELL DEFINED SURFACE CONVERGENCE BOUNDARY/DRY LINE WILL DEVELOP FROM CARBON COUNTY NORTH TO THE VICINITY OF CASPER ALONG WITH SE WINDS TO THE EAST OF THE BOUNDARY AND DRIER SW WINDS TO THE WEST. SOME STORMS WILL DEVELOP ALONG THIS BOUNDARY AND TRACK NORTH INTO JOHNSON COUNTY. LIFTED INDICES ARE PROGGED TO BE -6 IN NE JOHNSON ALONG WITH 1100J/KG. THE STORMS SHOULD BE OVER WITH FOR THE MOST PART BY 7 OR 8 PM OR SO ONCE THE VORT LOBE TRACKS RAPIDLY TO THE NORTHEAST OF THE CWA. WEAKER T STORMS SHOULD ALSO DEVELOP IN NW WY LATE THIS AFTERNOON AND EVENING CLOSER TO THE VORT LOBE. ON THURSDAY THE AFOREMENTIONED LOW WILL BE OFF THE NORTHERN CALIFORNIA OREGON COAST AND WILL EJECT A SLIGHTLY STRONGER VORT LOBE NORTHEAST ACROSS WY NW WY FOR SOME THUNDERSHOWER ACTIVITY IN NW WY THURSDAY AFTERNOON. TEMPERATURES WILL CONTINUE TO WARM EAST OF THE DIVIDE AND WILL REMAIN AROUND THE SAME WEST. THE REST OF THE CWA WILL BE DRY SLOTTED EXCEPT FOR JOHNSON COUNTY WHERE CAPES ARE SLATED TO BE 1150J/KG. WITH THE TROUGH APPROACHING FROM THE WEST AND RIDGE CONTINUING TO BUILD OVER THE PLAINS...DRY SOUTH WINDS WILL INCREASE FROM SOUTH CENTRAL TO NORTH CENTRAL WYOMING. BY FRIDAY THE UPPER LOW WILL EJECT YET A STRONGER ELONGATED VORT LOBE ACROSS NORTHWEST WY WHICH WILL PRODUCE MORE THUNDERSTORM ACTIVITY OVER NW WY WHERE LIFTED INDICES WILL BE AROUND -3. THUNDERSTORMS SHOULD ALSO ERUPT IN JOHNSON COUNTY WHERE LIFTED INDICES ARE PROGGED TO BE AROUND -4. BY FRIDAY NIGHT THE MODELS BEGIN TO DIVERGE IN THEIR SOLUTIONS. BY FRIDAY NIGHT THE GFS HAS THE UPPER LOW OVER SOUTHERN IDAHO AND THE SLOWER NAM OVER VEGAS. THE SLOWER NAM HAS THE ASSOCIATED SFC LOW OVER CENTRAL WY AND THE FASTER GFS HAS IT OVER SOUTHEAST WY WHICH WOULD RESULT IN A COOLER NORTHERLY FLOW. WILL INCREASE POPS FOR SHOWERS FOR THIS UNCERTAINTY. THE WARMING TREND WILL CONTINUE DURING THE DAY FRIDAY EAST OF THE DIVIDE WITH TEMPS REMAINING ABOUT THE SAME OR BECOMING A LITTLE COOLER WEST. .LONG TERM...SATURDAY THROUGH WEDNESDAY EXPECT MUCH COOLER TEMPERATURES WITH SHOWERS AND THUNDERSTORMS...MOST NUMEROUS ACROSS THE NORTH AND WEST...ON SATURDAY. SHOWERS WILL DECREASE FROM FROM THE SOUTH THROUGH SUNDAY MORNING. A WESTERLY FLOW PREVAILS MEMORIAL DAY THROUGH WEDNESDAY WITH A WARMING TREND...A RETURN TO NEAR NORMAL TEMPERATURES WITH LOW CHANCES OF SHOWERS AND LATE DAY THUNDERSTORMS ACROSS MAINLY THE NORTH HALF OF WYOMING. GFS AND GEM DETERMINISTIC RUNS CONTINUE TO BE MOST PROGRESSIVE LIFTING UPPER TROUGH OUT OF NORTHERN GREAT BASIN ACROSS WYOMING SATURDAY AND SATURDAY NIGHT WITH GEFS MEAN AND ECMWF ON THE SLOW END. FORECAST WEIGHTED TOWARD THE SLOWER SOLUTIONS. ECMWF HAS BACKED AWAY FROM STALLING OUT UPPER LOW OVER NORTHERN HIGH PLAINS LATE IN THE WEEKEND WITH FLATTER PROGRESSIVE UPSTREAM FLOW KEEPING THINGS MOVING ALONG. RATHER SLOW MOVING ANAFRONT PUSHES EAST ACROSS WYOMING SATURDAY WITH A LINE OF SHOWERS AND THUNDERSTORMS DEVELOPING ALONG THE FRONT FOLLOWED BY LOWERING SNOW LEVELS TO BETWEEN 7-8KFT IN THE WESTERN AND NORTHERN MOUNTAINS...WITH SHOWERS GRADUALLY LIFTING NORTHWARD THROUGH SATURDAY NIGHT. WESTERLY CONFLUENT FLOW PREVAILS ON SUNDAY WITH SOME RAIN AND SNOW SHOWERS LINGERING ACROSS THE NORTH MAINLY IN THE MORNING HOURS. A MUCH FLATTER ZONAL FLOW PREVAILS THROUGH THE MIDDLE OF NEXT WEEK WITH MEAN UPPER LOW NEAR 50N/140W UNDERCUT BY WESTERLIES WITH WEAK EMBEDDED SHORTWAVES ALONG 40-45N. ALL MODELS SHOW MEAN RIDGE DEVELOPING OVER THE ROCKIES BY TUESDAY WITH GFS SHOWING MORE AMPLIFICATION BY WEDNESDAY THAN ECMWF OR GEFS MEAN. FORECAST WEIGHTED TOWARD ZONAL FLOW/FLAT RIDGING WITH LOW CHANCE POPS MAINTAINED ACROSS THE NORTH THROUGH THE PERIOD. && .AVIATION... CONSIDERABLE MID/HIGH LEVEL CLOUDINESS IS EXPECTED TO SPREAD FROM WEST TO EAST TODAY. THESE CLOUDS ARE EXPECTED TO BE 15-25 KFT MSL...WITH LOWER VALUES ACROSS THE WEST. A FEW SHOWERS WILL BE POSSIBLE ACROSS THE WEST...BUT A DISTURBANCE AND A WEAK BOUNDARY COULD INITIATE ISOLATED STRONG THUNDERSTORMS ACROSS JOHNSON AND EASTERN NATRONA COUNTIES. KCPR COULD BE AFFECTED BY THESE THUNDERSTORMS...BUT MOST OF THE ACTIVITY IS EXPECTED TO BE EAST OR NORTH OF KCPR...WITH A BETTER CHANCE AFFECTING KBYG. HOWEVER...KCPR COULD EASILY BE AFFECTED BY OUTFLOW WINDS FROM NEARBY THUNDERSTORMS. VFR IS EXPECTED AT TAF SITES...WITH MVFR/IFR CONDITIONS IN/AROUND THUNDERSTORMS...AS WELL AS MVFR CEILINGS AT TIMES OVER WESTERN MOUNTAINS. MOUNTAIN TOPS OVER THE WEST WILL BECOME OBSCURED. && .FIRE WEATHER... A WARMING TREND IS IN STORE THROUGH THE END OF THE WEEK FOR AREAS EAST OF THE DIVIDE WITH TEMPERATURES WARMING AND THEN LEVELING OFF BY THURSDAY WEST OF THE DIVIDE. WIDELY SCATTERED TO SCATTERED THUNDERSTORMS CAN BE EXPECTED DURING THE AFTERNOONS...MAINLY IN THE EASTERN AND FAR WESTERN ZONES AS A SERIES OF UPPER LEVEL DISTURBANCES EJECT NORTHEAST FROM A PARENT LOW NOW OFF THE PACIFIC COAST. THE MINIMUM RELATIVE HUMIDITY WILL BE IN THE LOW TO MID TEENS IN SWEETWATER COUNTY THIS AFTERNOON WITH THESE LOWER MINIMUM RELATIVE HUMIDITIES SPREADING NORTH TO THE REST OF THE LOWER ELEVATIONS EXCEPT FOR THE FAR WEST. COOLER WETTER WEATHER MAY BE EXPECTED THIS WEEKEND AS THE PACIFIC LOW DRAWS NEAR. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...LIPSON LONG TERM...AEM AVIATION...WM FIRE WEATHER...LIPSON
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 642 AM MDT WED MAY 26 2010 WYZ001>020-022>030-271100- 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- 642 AM MDT WED MAY 26 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT WIDELY SCATTERED TO SCATTERED THUNDERSTORMS NATRONA AND JOHNSON COUNTIES AS WELL AS THE NORTHEAST BIG HORN BASIN AND BIG HORN MOUNTAINS LATE THIS AFTERNOON AND EARLY EVENING. A FEW STORMS ACROSS EASTERN JOHNSON COUNTY AND NORTHEAST NATRONA COUNTY COULD BECOME SEVERE WITH LARGE HAIL AND DAMAGING WIND. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY UNSEASONABLY WARM TEMPERATURES ARE EXPECTED THURSDAY AND FRIDAY THAT WILL LIKELY ACCELERATE SNOWMELT IN THE EASTERN WIND RIVER AND EASTERN BIG HORN MOUNTAINS WHERE SNOWPACK REMAINS WELL ABOVE AVERAGE. RIVERS AND CREEKS IN THESE AREAS WILL LIKELY EXPERIENCE SIGNIFICANT RISES LATE THIS WEEK. A SIGNIFICANT NEW STORM SYSTEM WILL MOVE SLOWLY INTO THE GREAT BASIN THURSDAY INTO FRIDAY AND ACROSS WYOMING SATURDAY AND SUNDAY. THIS STORM SYSTEM WILL BRING A HIGH LIKELIHOOD OF PRECIPITATION WITH IT AS IT MOVES SLOWLY ACROSS WESTERN AND CENTRAL WYOMING. SHOWERS AND A FEW THUNDERSTORMS WILL MOVE INTO THE WEST AS EARLY AS THURSDAY AND THEN INCREASE INTO FRIDAY. PRECIPITATION WILL BECOME MORE WIDESPREAD AND THEN MOVE EAST OF THE DIVIDE FRIDAY INTO SATURDAY ALONG WITH SHARPLY COLDER TEMPERATURES. MUCH COLDER AIR WILL FILTER INTO NORTHWEST WYOMING WHERE A COLD VALLEY RAIN AND MOUNTAIN SNOW IS EXPECTED FRIDAY THROUGH SATURDAY...INCLUDING YELLOWSTONE NATIONAL PARK. SHOWERS WILL LIKELY DEVELOP ACROSS MUCH OF CENTRAL AND NORTH CENTRAL WYOMING ON SATURDAY AND LINGER ACROSS NORTH CENTRAL WYOMING INTO SUNDAY. STAY TUNED THROUGHOUT THE WEEK FOR UPDATES ON THIS RAPID TRANSITION FROM WARM AND DRY TO WET AND COLDER ONCE AGAIN FOR THE MEMORIAL DAY WEEKEND. CONDITIONS HOWEVER WILL LIKELY IMPROVE CONSIDERABLY FOR MEMORIAL DAY. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY STREAMS OR RIVERS RISING RAPIDLY OR NEAR BANKFULL. THANK YOU. TEAM RIVERTON
The Riverton/Lander radar (KRIW), 178 km away, was scanning. The volume nearest the first event began at 20:08 UTC.
1 hail. Local standard time, as filed.
A strong thunderstorm formed on Casper Mountain and produced penny sized hail as it moved north through Casper.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2010Every state in 2010This day in weather historyWarnings in Wyoming, May 2010
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: 229271.