A thunderstorm formed over the Bighorn Mountains. As it moved southeast it encountered higher dew point air and become severe.
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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 formed over the Bighorn Mountains. As it moved southeast it encountered higher dew point air and become severe. The storm then drifted southeast and then south as it turned right and produced hail for over 2 hours. Penny size hail was common along it's path with the largest hail reported was quarter size around Linch.
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 Jul 12, 12:53 PM MST, 1 hour 13 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 153 PM MDT Thu Jul 12 2018 .SHORT TERM...(This evening through Friday) Issued at 130 PM MDT Thu Jul 12 2018 Two distinct areas of thunderstorms are occurring ATTM in Wyoming. One area is over Southeast Wyoming that appears to be left over from the weak circulation/vort max now centered over Northeast Colorado. The other area of storms is associated with trailing shortwave making its way east across the Northern Rockies asct with the closed low tracking east across Canada. This area started out as an area of elevated convection across far Western Wyoming and has now transitioned into an area of sfc based convection across an area now extending from the Northern Lincoln/Sweetwater County border to near Beaver Rim. As this shortwave makes its way east across the rest of the CWA, it will encounter higher capes resulting in heavier rainers for the remainder of the afternoon and evening. As for Friday, only isold convection is expected over Natrona/Johnson Counties including the Big Horn Mtns as the shortwave exits east but the westerly steering flow remaining difluent. Friday will be warmer with highs in the low 90s east of the divide and low 80s in the far west valleys. .LONG TERM...(Friday night through Thursday) Issued at 130 PM MDT Thu Jul 12 2018 Weak west flow aloft will dominate the weather pattern through the extended with a series of weak cold fronts coming south out of Montana as short wave troughs move east across southern Canada and Montana brushing northern Wyoming. With time the timing of these troughs and cold fronts diverge in the extended models with significant differences by Wednesday and Thursday. Friday night and Saturday will be dry and warmer with a cold front cooling temperatures 10 to 15 degrees on Sunday with increasing chances of showers and thunderstorms. Some showers and thunderstorms will be a threat Monday through Wednesday with gradual warming expected. && .AVIATION...(For the 00Z TAFS through 00Z Saturday) Issued at 130 PM MDT Thu Jul 12 2018 Isolated showers and thunderstorms have developed over Western Wyoming and will push east across portions of Central and East Central Wyoming with KCPR and KBYG likely seeing the best chc of any thunderstorm activity through this evening. Winds will generally be light except for some gusty winds near showers and thunderstorms. Skies will clear after sunset this evening. Only isolated thunderstorms are expected across portions of Natrona/Johnson Counties after 18z Friday. Otherwise expect VFR conditions Friday. && .FIRE WEATHER... Issued AT 130 PM MDT Thu Jul 12 2018 Fire weather concerns should remain below critical for the rest of today. Relative humidity will remain above critical levels with winds remaining light to moderate for the most part. There will be another round of afternoon and evening showers and thunderstorms East of the Divide as well as across Southern Wyoming during the rest of today. However, coverage should be less then previous days. Mixing and smoke dispersal will be generally fair to good. Except for very isolated thunderstorm activity in zones 280/281/ and 300 Friday afternoon, expect dry conditions Friday. Temperatures will be around 5 degrees warmer Friday. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...Lipson LONG TERM...Baker AVIATION...Lipson FIRE WEATHER...Lipson
Hazardous Weather Outlook National Weather Service Riverton WY 124 AM MDT Thu Jul 12 2018 WYZ001>020-022>030-131345- 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- 124 AM MDT Thu Jul 12 2018 This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight Isolated to widely scattered thunderstorms, mainly in the afternoon and evening East of the Divide. .DAYS TWO THROUGH SEVEN...Friday through Wednesday Saturday...Isolated thunderstorms over the north late and at night. Elevated fire weather concerns south. Sunday and Monday...Isolated thunderstorms mainly along and east of the Continental Divide. .SPOTTER INFORMATION STATEMENT... Spotters are urged to report hail, wind gusts over 45 mph and heavy rainfall. Thank you.
Special Weather Statement National Weather Service Riverton WY 1125 AM MDT THU JUL 12 2018 WYZ024-026-121800- Upper Green River Basin-Salt River and Wyoming Ranges- 1125 AM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN SUBLETTE COUNTY UNTIL NOON MDT... At 1125 AM MDT, Doppler radar was tracking a strong thunderstorm 8 miles north of Calpet, or 11 miles southwest of Big Piney, moving east at 15 mph. Half inch hail and winds in excess of 40 mph will be possible with this storm. This storm will remain over mainly rural areas of southwestern Sublette County. PRECAUTIONARY/PREPAREDNESS ACTIONS... Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 4229 11036 4253 11037 4258 10989 4228 10988 TIME...MOT...LOC 1725Z 265DEG 15KT 4240 11026 Baker
Special Weather Statement
National Weather Service Riverton WY
205 PM MDT THU JUL 12 2018
WYZ030-122045-
East Sweetwater County-
205 PM MDT THU JUL 12 2018
...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL SWEETWATER COUNTY UNTIL
245 PM MDT...
At 203 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles northwest of Superior, or 20 miles northeast of Rock Springs,
moving southeast at 5 mph.
Half inch hail and winds in excess of 30 mph will be possible with
this storm.
This strong thunderstorm will be near...
Superior around 245 PM MDT.
This includes Interstate 80 between mile markers 115 and 120.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. An estimated three quarters of an inch of
rainfall has likely occurred in some areas with this storm. Do not
drive your vehicle through flooded roadways.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 4162 10906 4187 10913 4187 10907 4189 10900
4191 10897 4192 10895 4178 10873
TIME...MOT...LOC 2003Z 326DEG 5KT 4185 10903
LipsonSpecial Weather Statement National Weather Service Riverton WY 210 PM MDT THU JUL 12 2018 WYZ009-010-122100- Northeast Johnson County-Bighorn Mountains Southeast- 210 PM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL JOHNSON COUNTY UNTIL 300 PM MDT... At 209 PM MDT, Doppler radar was tracking a thunderstorm along Highway 16 just west of Buffalo, moving east at 20 mph. Half inch hail and winds in excess of 30 mph will be possible with this storm. This strong thunderstorm will be near... Buffalo around 230 PM MDT. Other locations impacted by this storm include Buffalo Johnson County Airport and Johnson County Fairgrounds. This includes the following highways... Interstate 25 between mile markers 292 and 299. Interstate 90 between mile markers 53 and 64. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 4424 10689 4431 10699 4447 10663 4425 10658 TIME...MOT...LOC 2009Z 258DEG 16KT 4433 10681 Lipson
Special Weather Statement National Weather Service Riverton WY 250 PM MDT THU JUL 12 2018 WYZ009>011-122130- Southeast Johnson County-Northeast Johnson County-Bighorn Mountains Southeast- 250 PM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL JOHNSON COUNTY UNTIL 330 PM MDT... At 248 PM MDT, Doppler radar was tracking a strong thunderstorm 14 miles south of Buffalo, moving southeast at 30 mph. Three quarters of an inch diameter hail and winds in excess of 30 mph will be possible with this storm. This storm will remain over mainly rural areas of central Johnson County. This includes Interstate 25 between mile markers 277 and 291. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Over one inch of estimated rainfall has likely occurred in portions of this storm. Do not drive your vehicle through flooded roadways. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. && LAT...LON 4421 10689 4427 10675 4411 10641 4399 10674 TIME...MOT...LOC 2048Z 319DEG 24KT 4413 10669 Lipson
Special Weather Statement National Weather Service Riverton WY 254 PM MDT THU JUL 12 2018 WYZ011-122145- Southeast Johnson County- 254 PM MDT THU JUL 12 2018 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL JOHNSON COUNTY UNTIL 345 PM MDT... At 253 PM MDT, Doppler radar was tracking a strong thunderstorm 7 miles east of Mayoworth, or 11 miles north of Kaycee, moving east at 5 mph. Half inch hail and winds in excess of 30 mph will be possible with this storm. This storm will remain over mainly rural areas of south central Johnson County. This includes Interstate 25 between mile markers 261 and 270. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. An estimated three quarters of an inch of rainfall has occurred in portions of this storm. Do not drive your vehicle through flooded roadways. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. && LAT...LON 4384 10671 4394 10673 4397 10641 4372 10645 TIME...MOT...LOC 2053Z 277DEG 4KT 4387 10665 Lipson
The Riverton/Lander radar (KRIW), 188 km away, was scanning. The volume nearest the first event began at 21:07 UTC.
1 hail. Local standard time, as filed.
Hail fell along the path of a long lived thunderstorms as it traveled southeastward through Johnson County. The largest hail recorded was 1 inch around Linch.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2018Every state in 2018This day in weather historyWarnings in Wyoming, July 2018
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: 758422.