A thunderstorm developed along a frontal boundary over eastern Park County. There was sufficient wind shear to generate a thunderstorm that produced a rope tornado over open country near US Highway 14/16/20.
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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 thunderstorm developed along a frontal boundary over eastern Park County. There was sufficient wind shear to generate a thunderstorm that produced a rope tornado over open country near US Highway 14/16/20. The tornado caused no damage; however, the associated thunderstorm did produce nickel sized hail that fell on the highway and was several inches deep.
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 16, 10:05 AM MST, 2 hours 8 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 1105 AM MDT SAT MAY 16 2015 .SHORT TERM...SATURDAY THROUGH MONDAY NIGHT IT WAS ANOTHER VERY ACTIVE DAY YESTERDAY WITH FUNNEL CLOUDS...HAILSTORMS...SOME FLOODING AND EVEN HIGHER ELEVATIONS SNOW. IN OTHER WORDS...IT WAS MAY IN WESTERN AND CENTRAL WYOMING. AS OF NOW...A DRY SLOT HAS WORKED ITS WAY ACROSS MOST OF THE AREA WITH QUIET CONDITIONS WITH THE EXCEPTION OF THE NORTHWEST CORNER WHERE SOME WRAP AROUND MOISTURE CONTINUES TO BRING SOME MAINLY LIGHT PRECIPITATION AT THIS TIME. IN ADDITION...WITH THE RAIN AND SOME CLEARING SKIES...PATCHY FOG HAS DEVELOPED ACROSS AREAS THAT SAW THE HEAVIEST PRECIPITATION YESTERDAY. AS FOR TODAY...BOTH THE NAM AND GFS ARE FAIRLY CONSISTENT IN KEEPING THE VAST MAJORITY OF PRECIPITATION ACROSS NORTHERN AND WESTERN AREAS THROUGH MOST OF TODAY. IN THE WEST...RAIN AND SNOW SHOWERS WILL CONTINUE. AS FOR SNOW LEVELS...THE MODELS HAVE TRENDED A BIT WARMER WITH 700 MILLIBAR TEMPERATURES ONLY FALLING TO AROUND MINUS 1 TO MINUS 2 BY THE END OF THE DAY. THIS WOULD HOLD SNOW LEVELS ABOVE 7500 FEET AND A LOT OF THE SNOW WOULD NOT STICK WITH THE STRONG MAY SUN. MEANWHILE...EAST OF THE DIVIDE WE HAVE KEPT A SLIGHT CHANCE IN FOR LATE DAY SHOWERS AND THUNDERSTORMS WITH A DECENT AMOUNT OF MOISTURE AT THE SURFACE AND SOME FORCING FROM A COLD FRONT THAT WILL MOVE TOWARD THE AREA. LIKE YESTERDAY...ANY STORM COULD HAVE SOME GUSTY WINDS...HAIL AND EVEN SOME HEAVY RAINS. HOWEVER...MANY AREAS WILL BE DRY A VAST MAJORITY OF THE DAY...ESPECIALLY THE FURTHER SOUTH AND EAST YOU GO. FOR TONIGHT...THE FRONT WILL MOVE SOUTHEASTWARD ACROSS THE STATE AND BRING IN SOME COOLER AIR. AGAIN...THE MODELS HAVE TRENDED A BIT WARMER WITH 700 MILLIBAR TEMPERATURES A BIT HIGHER THAN YESTERDAY. SO...SNOW LOOKS TO HOLD ABOVE 7000 FEET WITH ANY DECENT ACCUMULATION ABOVE 9000 FEET. THERE IS A CHANCE SOME AREAS WOULD COME IN WITH ADVISORY LEVEL AMOUNTS...BUT SINCE IMPACTS WOULD BE MINIMAL...WE WILL NOT ISSUE ANY. OTHERWISE...EXPECT MOSTLY CLOUDY AND UNSETTLED CONDITIONS WITH SHOWERS POSSIBLE ACROSS MOST AREAS WITH A GUSTY WIND DEVELOPING ACROSS AREAS FAVORED WITH NORTH TO NORTHWESTERLY FLOW AND STRONG COLD ADVECTION SUCH AS THE NORTHERN BIG HORN BASIN AND NORTHERN JOHNSON COUNTY. SUNDAY ALSO LOOKS LIKE A MOSTLY CLOUDY AND COLD DAY WITH A CONTINUING CHANCE OF SHOWERS ACROSS MOST OF THE AREA ALONG WITH CONTINUED GUSTY WINDS ACROSS THE AFOREMENTIONED AREAS. CONTINUITY LOOKED REASONABLE FOR THIS DAY SO WE MADE FEW CHANGES. SHORTWAVE RIDGING THEN MOVES ACROSS THE STATE FOR SUNDAY NIGHT TO HELP SHUT OFF THE SHOWERS. HOWEVER...THE DRY PERIOD LOOKS TO BE SHORT LIVED AS ANOTHER SURGE OF MOISTURE MOVES IN FROM THE SOUTHWEST FOR MONDAY. AT THIS TIME...BOTH THE NAM AND GFS HOLD MOST OF THE MOISTURE WEST OF THE DIVIDE FOR MONDAY. AS A RESULT WE DID TRIM POPS BACK A BIT FOR MONDAY DURING THE DAY EAST OF THE DIVIDE. WE ALSO DECREASED SKY COVER A BIT AND RAISED TEMPERATURES A COUPLE OF DEGREES. .LONG TERM...TUESDAY THROUGH SATURDAY SYNOPSIS...COOL AND SHOWERY WEATHER WITH ISOLATED TO SCATTERED AFTERNOON/EVENING THUNDERSTORMS WILL CONTINUE ACROSS THE AREA THROUGH THIS PERIOD. DISCUSSION...A SERIES OF PACIFIC STORM SYSTEMS WILL CONTINUE TO UNDERCUT A BLOCKING RIDGE OVER WESTERN CANADA THROUGH THIS PERIOD. THE STORM TRACK WILL REMAIN RELATIVELY UNCHANGED WITH UPPER LOWS DIVING DOWN THE WEST COAST INTO THE SOUTHWEST U.S. BEFORE LIFTING NE ACROSS THE GREAT BASIN/CENTRAL ROCKIES. THE NEXT IN THIS SERIES OF STORM SYSTEMS (IN THE NE PACIFIC CROSSING 140W EARLY THIS MORNING) WILL BE CENTERED NEAR LAS VEGAS BY 12Z TUESDAY WITH SHORTWAVE EJECTING OUT AHEAD THIS SYSTEM NE ACROSS COLORADO INTO WYOMING/WESTERN NEBRASKA DURING THE DAY. AIRMASS EXPECTED TO BE ONLY SLIGHTLY UNSTABLE AHEAD OF THIS SYSTEM WITH SFC HIGH PRESSURE OVER THE NORTHERN PLAINS...RESULTING IN NUMEROUS SHOWERS BUT THUNDERSTORMS SHOULD REMAIN ISOLATED AND BELOW SEVERE THRESHOLDS. THE MAIN UPPER LOW IS EXPECTED TO SHEAR OUT ACROSS THE AREA ON WEDNESDAY KEEPING SCT SHOWERS OVER MOST OF THE AREA. HIGHS BOTH TUESDAY AND WEDNESDAY WILL BE 10-15F BELOW NORMAL ACROSS MOST AREAS...OR HIGHS MOSTLY IN THE 50S ACROSS THE LOWER ELEVATIONS. A BRIEF LETUP IN SHOWER ACTIVITY IS EXPECTED WEDNESDAY NIGHT INTO THURSDAY MORNING BETWEEN SYSTEMS...WITH NEXT PACIFIC SYSTEM MOVING ONTO (GFS) OR NEAR THE SOUTHERN CALIFORNIA COAST (ECMWF) THURSDAY. SOUTHERLY DIFLUENT FLOW AHEAD OF THIS SYSTEM AND SLIGHT INSTABILITY WILL RESULT IN SCT SHOWERS AND THUNDERSTORMS ACROSS MOST AREAS THURSDAY AFTN/EVE...POSSIBLY LESS ACTIVITY OVER THE NORTH AND EAST WHERE A DRIER AND MORE STABLE AIRMASS IS EXPECTED. THIS SYSTEM WILL THEN SLOWLY PROGRESS INTO THE GREAT BASIN/CENTRAL ROCKIES FRIDAY AND SATURDAY...SO AT LEAST THE START OF MEMORIAL DAY WEEKEND IS LOOKING LIKE MOST MEMORIAL DAY WEEKENDS IN WYOMING...COOL AND WET. && .AVIATION.../18Z ISSUANCE/ SHOWERS WITH SOME HIGH MOUNTAIN SNOWS FOR NW WY TODAY...DECREASING IN COVERAGE AFTER 00Z. EXPECT VFR TO MVFR CONDITIONS OVER FAR NORTH AND WEST WY THROUGH ABOUT 09Z SUNDAY WITH VCFG VCSH AND FREQUENT MOUNTAIN OBSCURATION...IMPROVING AFTER 15Z SUNDAY. SHOWERS AND PERHAPS A COUPLE OF THUNDERSTORMS WILL FORM IN SOUTHWEST/SOUTHERN WY THIS AFTERNOON AND CONTINUE INTO THE EVENING. ISOLATED TO SCATTERED SHOWERS WILL DEVELOP OVER THE REST OF THE REGION AFTER 21Z...CONTINUING THROUGH 04Z SUNDAY. TERMINAL SITES IN THE CENTRAL BASINS WILL BE LESS LIKELY TO BE AFFECTED BY THE SHOWERS. EXPECT AREAS OF MVFR CONDITIONS IN SW WY AFTER 00Z...THEN AREAS OF MVFR CONDITIONS WILL DEVELOP EAST OF THE DIVIDE AFTER 07Z AS COLDER AIR ASSOCIATED WITH A COLD FRONT AIDS IN LOW SOME LOW CLOUD FORMATION. && .FIRE WEATHER... FIRE DANGER RELATIVELY LOW THROUGH THE WEEKEND AS SEASONAL TO COOL AND RELATIVELY MOIST CONDITIONS PERSIST. HOWEVER...IT WILL BE UNSTABLE AGAIN TODAY...OFFERING UP CHANCES FOR MORE THUNDERSTORMS AND ASSOCIATED LIGHTNING. SNOWS IS LIKELY TO RETURN TO THE HIGHER ELEVATIONS AGAIN THIS WEEKEND WITH SNOW LEVELS LOWERING TO AROUND 7000 FEET AT TIMES. AFTER A SHORT BREAK SUNDAY NIGHT...MORE SHOWERS ARE POSSIBLE WEST OF THE DIVIDE FOR MONDAY. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...HATTINGS LONG TERM...AEM AVIATION...BRAUN FIRE WEATHER...HATTINGS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MDT SAT MAY 16 2015 WYZ001>020-022>030-171100- 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 SAT MAY 16 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT ISOLATED TO SCATTERED LATE DAY AND AFTERNOON THUNDERSTORMS...SOME WITH HAIL...GUSTY WINDS AND HEAVY RAIN. SOME ACCUMULATING SNOW IS POSSIBLE IN THE NORTHWESTERN MOUNTAINS TODAY AND ALL NORTHERN MOUNTAIN RANGES TONIGHT. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY SUNDAY...SNOWFALL POSSIBLE OVER THE NORTHERN MOUNTAINS. MONDAY...ISOLATED TO LOCALLY SCATTERED THUNDERSTORMS...MAINLY OVER THE WEST AND SOUTHWEST. TUESDAY AND WEDNESDAY...ANOTHER STORM SYSTEM WILL LIKELY BRING INCREASING SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE AREA TUESDAY WITH MOUNTAIN SNOW AND VALLEY RAIN SHOWERS OVER THE REGION WEDNESDAY. THURSDAY AND FRIDAY...ISOLATED TO SCATTERED AFTERNOON AND EVENING THUNDERSTORMS. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE URGED TO REPORT STRONG WIND GUSTS...HAIL...AS WELL AS HEAVY RAINFALL OVER A HALF AN INCH. THANK YOU. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 1212 PM MDT SAT MAY 16 2015 WYZ002-003-162000- ABSAROKA MOUNTAINS-CODY FOOTHILLS- 1212 PM MDT SAT MAY 16 2015 SHOWERS AND A COUPLE OF THUNDERSTORMS ARE DEVELOPING ACROSS THE AREAS MOUNTAINS AND ADJACENT CODY FOOTHILLS THIS AFTERNOON. THESE SHOWERS AND STORMS ARE MOVING EAST SLOWLY AT 10 TO 15 MPH. THE MAIN THREATS FROM THIS ACTIVITY WILL BE BRIEF HEAVY RAIN...SMALL HAIL AND FREQUENT LIGHTNING. JB
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
105 PM MDT SAT MAY 16 2015
WYZ003-004-161945-
CODY FOOTHILLS WY-NORTH BIG HORN BASIN WY-
105 PM MDT SAT MAY 16 2015
...SIGNIFICANT WEATHER ADVISORY FOR EASTERN PARK COUNTY UNTIL 145 PM
MDT...
AT 100 PM MDT...LOCAL LAW ENFORCEMENT REPORTED A STRONG THUNDERSTORM
NEAR HWY 14/16/20 MILE MARKER 70...WHICH IS 16 MILES EAST OF CODY...
MOVING SOUTHEAST AT 15 MPH.
A FUNNEL CLOUD IS EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN
AND FREQUENT DANGEROUS LIGHTNING.
THIS STORM WILL BE NEAR...
RURAL EASTERN PARK COUNTY THROUGH 145 PM MDT
IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.
BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A
FLOODED ROADWAY.
REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN
RIVERTON AT 1-800-211-1448.
LAT...LON 4461 10869 4449 10856 4417 10857 4413 10864
4451 10890
TIME...MOT...LOC 1904Z 328DEG 11KT 4448 10873
BRAUNPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RIVERTON WY
109 PM MDT SAT MAY 16 2015
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0100 PM FUNNEL CLOUD 15 E CODY 44.52N 108.75W
05/16/2015 PARK WY LAW ENFORCEMENT
BLM LAW ENFORCEMENT REPORTED A FUNNEL CLOUD NEAR THE
PARK/BIG HORN COUNTY LINE JUST NORTH OF U.S. HIGHWAY 16.
&&
CJONESSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
111 PM MDT SAT MAY 16 2015
WYZ003-004-162000-
CODY FOOTHILLS WY-NORTH BIG HORN BASIN WY-
111 PM MDT SAT MAY 16 2015
...SIGNIFICANT WEATHER ADVISORY FOR EASTERN PARK COUNTY UNTIL 200 PM
MDT...
AT 112 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM NEAR HWY 14/16/20 MILE MARKER 70...WHICH IS 16
MILES EAST OF CODY...MOVING SOUTHEAST AT 5 MPH.
HAIL UP TO ONE-HALF INCH IN DIAMETER AND FUNNEL CLOUDS ARE EXPECTED
WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS
LIGHTNING.
THIS STORM WILL BE NEAR...
HWY 14/16/20 MILE MARKER 70 AROUND 120 PM MDT.
IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.
BRIEF HEAVY RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES
AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A
FLOODED ROADWAY.
REPORT HAZARDOUS WEATHER TO THE NATIONAL WEATHER SERVICE OFFICE IN
RIVERTON AT 1-800-211-1448.
LAT...LON 4461 10869 4449 10857 4432 10857 4424 10877
4452 10891
TIME...MOT...LOC 1911Z 331DEG 4KT 4448 10874
BRAUNThe national radar mosaic for the moment the first event began.
1 tornado, 1 hail. Local standard time, as filed.
A Bureau of Land Management law enforcement officer reported a rope tornado in eastern Park County. The tornado remained over open country and caused no damage. The twister was photographed from both the west and east sides.
A trained spotter reported hail up to the size of nickels covering US Highway 14/16/20 near milepost 71.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2015Every state in 2015This day in weather historyThe tornado archive for Wyoming, 2015Warnings in Wyoming, May 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: 570224, 570223.