Numerous slow moving thunderstorms developed across central Wyoming and some became severe. On severe thunderstorm crossed US 20 26 in eastern Fremont County and brought ping pong ball size hail that damaged a pick up truck.
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.
Numerous slow moving thunderstorms developed across central Wyoming and some became severe. On severe thunderstorm crossed US 20 26 in eastern Fremont County and brought ping pong ball size hail that damaged a pick up truck. Another storm produced a 62 mph near Linch in Johnson County. In Worland Wyoming, over an inch of rain and small hail fell in only 25 minutes and brought street flooding that backed into several buildings in town.
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 Aug 21, 1:22 PM MST, 1 hour 32 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 222 PM MDT Wed Aug 21 2019 .SHORT TERM...(This evening through Thursday) Issued at 220 PM MDT Wed Aug 21 2019 Today the west and southwest continue to be hot and dry with RH values in the teens to even a few single digits. Highlights are not out for today as winds will still be too light. The bigger story today is instead the threat for strong to possibly severe storms across central and northern WY. RH and dewpoints are both higher on the eastern side of the Divide mainly thanks to the boundary that previously moved into those areas yesterday. Skies were clear this morning and there is plenty of time for heating and instability to grow. With this set up of moister air and growing instability the weak shortwave moving into the area fired off a few storms even sooner than previously anticipated. Storms have been mainly sticking to the mountains and have decreased in strength when moving into lower elevations. Based on mesoscale analysis, NAM was indeed a bit too aggressive with CAPEs and GFS has done a better job with predicting 2000 J/kg. Both the NAM and HRRR have showers and storms lingering in eastern areas the longest with all activity ending by 06Z. The main threat from any storm will be strong winds and some smaller hail, but even weaker showers could produce strong gusts when they collapse and die. Thursday morning, the upper level trough axis should be over Idaho. This trough is bringing a cold front, increased moisture and precipitation chances, and also will tighten the pressure gradient. As just the tail end of the system will impact WY, the northern third of the state has the greatest chance of showers and thunderstorms. Southwestern WY will remain dry. Breezy winds will develop across the state as the pressure gradient tightens through the day with the approach of the system. Wind gusts will be strongest across southern portions; gusts 30 mph to 35 mph are currently expected. With the moisture from this system confined to the north and a mostly west flow prevailing in the south, RH values will once again be in the teens to single digits across the south. The low RH and gusty winds will combine to create critical fire weather during the afternoon and evening hours. .LONG TERM...(Thursday night through Wednesday) Issued at 202 PM MDT Wed Aug 21 2019 On Thursday night, the strong shortwave trough axis will track across the CWA. The models are still indicating -7 lifted indices over Johnson County by 00Z Friday along with elevated capes. Strong thunderstorms are still possible well into the evening in Johnson County Thursday evening. The NAM is the fastest bringing the trough axis through Thursday night with the other models bringing it through Friday, along with a mid and upper level low trying to cut off over Northern Wyoming Friday, but should be inconsequential with lack of moisture. High temperatures will be several degrees cooler Friday east of the divide behind the trough axis and associated weak cool front due to come through Thursday night. Winds with this strong shortwave will likely extend the critical fire weather conditions into Friday along with the low RH behind the trough axis. By Saturday, we will be in a well established zonal flow as a fast west northwest flow establishes over the Northwest quarter of the US including Wyoming. A fast moving shortwave within the flow could be enough to kick of some thunderstorm activity in our northeast zones Saturday evening and to a lesser extent late Sunday. Otherwise, the winds will be the most prominent feature with this next shortwave as winds surface under the right front quad of the associated jet max. These winds will usher in drier air so Sunday is shaping up to be another potentially critical fire weather day. Temperatures will increase Sunday as well, with highs in the 90s east and 80s west. Similar conditions are expected Monday with continued breezy conditions as another ripple in the flow keeps the gradient rather tight, but with slightly higher RH and decreased temperatures. The models are struggling with the timing and placement of the next shortwave feature for Tue/Wed. The GFS keeps the jet well to our northeast and without a shortwave feature to speak of for our area. The Euro tracks this next shortwave through us Tuesday and the Canadian Wednesday. With the uncertainty of the models, kept very low pops in the north and northeast for Tuesday and Tuesday night. The steering winds will be from the north northwest behind this trough coincident with an associated cold front, so at some point during the middle of next week, we should see a trend of noticeably cooler weather as 700mb temps begin to drop to 6C. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 202 PM MDT Wed Aug 21 2019 All is quiet currently and light winds and VFR conditions are widespread, but showers and thunderstorms will begin to develop east of the Divide between 18Z and 19Z, clouds are already starting to build. Thunderstorms will develop around the Absaroka/Wind River mountains, and shift eastward through the afternoon and evening. Terminals most likely to be impacted are KCOD, KLND, KRIW, KWRL and KCPR; VCTS is forecasted for those terminals. Gusty to strong winds will be the main threat from storms and brief MVFR/IFR conditions are possible with any convection. Activity should be over by 06Z/07Z. Thursday morning will be quiet with light winds, but gusts will develop in the afternoon. && .FIRE WEATHER... Issued AT 202 PM MDT Wed Aug 21 2019 ...Multiple Fire Weather Watches for Thursday afternoon across southwest Wyoming... Conditions today will be similar to Tuesday with isolated to scattered thunderstorms returning mainly over the mountains during the remainder of this afternoon. Some storms may be strong with gusty winds being the main threat. West of the Divide will remain hot and dry this afternoon, with poor RH recovery tonight. Winds will be stronger today than Tuesday but not to the point of causing fire concerns. Thursday will see a cold front push across Wyoming east of the Divide. This will bring more afternoon showers and thunderstorms east of the Divide, mainly in zones 281 and 285, and increase winds in the still very dry areas west of the Divide. A Red Flag Warning has been issued for many fire zones along and west of the Divide for Thursday afternoon and evening. These critical fire weather conditions will extend into Friday across the southern zones. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from noon Thursday to 8 PM MDT Friday for WYZ277>279. Red Flag Warning from noon to 8 PM MDT Thursday for WYZ288-289. && SHORT TERM...Bourque LONG TERM...Lipson AVIATION...Bourque FIRE WEATHER...Lipson
Hazardous Weather Outlook National Weather Service Riverton WY 337 PM MDT Wed Aug 21 2019 WYZ001>020-022>030-221200- 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- 337 PM MDT Wed Aug 21 2019 ...RED FLAG WARNING for Southwest Wyoming West of the Divide Valid from 12 Noon Thursday through 8 PM Friday... ...RED FLAG WARNING for Portions of Central Wyoming East of the Divide Valid from 12 Noon Thursday through 8 PM Thursday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Isolated to widely scattered thunderstorms are possible this afternoon in north and central Wyoming. Some storms could become strong with the main threat being gusty winds. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Thursday...Isolated to widely scattered thunderstorms in the north. Strong gusty winds and low relative humidities in southwest Wyoming as well as across portions of Central Wyoming east of the Divide is expected. A Red Flag Warning has been issued for much of the areas west of the Continental Divide, as well as portions of Central Wyoming east of the Divide. Friday...Strong gusty winds and low relative humidities in southwest Wyoming. A Red Flag Warning has been issued for much of the areas west of the Continental Divide. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. TEAM RIVERTON
Special Weather Statement
National Weather Service Riverton WY
104 PM MDT Wed Aug 21 2019
WYZ009-211930-
Bighorn Mountains Southeast-
104 PM MDT Wed Aug 21 2019
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN JOHNSON COUNTY UNTIL
130 PM MDT...
At 103 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles north of Powder River Pass, which is 16 miles west of Buffalo,
moving southeast at 10 mph.
Half inch hail and winds 30 mph to 40 mph will be possible with this
storm.
This storm will remain over mainly rural areas of northwestern
Johnson County, including the following locations... South Fork
Campground.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Heavy rainfall is also occurring with this storm, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4413 10700 4429 10711 4431 10711 4440 10704
4429 10681 4428 10682 4427 10681
TIME...MOT...LOC 1903Z 315DEG 8KT 4428 10703
BourqueSpecial Weather Statement
National Weather Service Riverton WY
125 PM MDT Wed Aug 21 2019
WYZ009-212015-
Bighorn Mountains Southeast-
125 PM MDT Wed Aug 21 2019
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN JOHNSON COUNTY UNTIL
215 PM MDT...
At 125 PM MDT, Doppler radar was tracking a thunderstorm 9 miles
north of Cloud Peak, which is 21 miles southwest of Sheridan, moving
southeast 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 northwestern
Johnson County.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
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 4449 10688 4440 10706 4434 10710 4454 10725
4456 10722 4456 10708
TIME...MOT...LOC 1925Z 313DEG 11KT 4451 10714
LipsonSpecial Weather Statement
National Weather Service Riverton WY
246 PM MDT Wed Aug 21 2019
WYZ006-008-212115-
Southeast Big Horn Basin-Bighorn Mountains West-
246 PM MDT Wed Aug 21 2019
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN WASHAKIE COUNTY
UNTIL 315 PM MDT...
At 246 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles northeast of Cottonwood Pass, which is 32 miles south of Ten
Sleep. This storm was nearly stationary.
Half inch hail will be possible with this storm.
This storm will remain over mainly rural areas of southeastern
Washakie County.
LAT...LON 4353 10724 4348 10725 4348 10753 4366 10756
4366 10723 4355 10724
TIME...MOT...LOC 2046Z 176DEG 2KT 4356 10742
MyersSpecial Weather Statement
National Weather Service Riverton WY
330 PM MDT Wed Aug 21 2019
WYZ017-212200-
Wind River Basin-
330 PM MDT Wed Aug 21 2019
...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL FREMONT COUNTY UNTIL
400 PM MDT...
At 329 PM MDT, Doppler radar was tracking an area of strong
thunderstorms near Moneta, which is 18 miles east of Shoshoni. This
storm was nearly stationary.
Half inch hail will be possible with this storm.
This strong thunderstorm will be near...
Lysite around 345 PM MDT.
LAT...LON 4299 10766 4323 10793 4334 10767 4318 10751
4313 10752 4313 10750 4306 10751
TIME...MOT...LOC 2129Z 121DEG 4KT 4318 10775
MyersSpecial Weather Statement National Weather Service Riverton WY 341 PM MDT Wed Aug 21 2019 WYZ003-212215- Cody Foothills- 341 PM MDT Wed Aug 21 2019 ...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL PARK COUNTY UNTIL 415 PM MDT... At 339 PM MDT, Doppler radar was tracking a thunderstorm over Cody producing very heavy rainfall and some small hail. This storm was moving northeast at 5 to 10 mph. This storm could produce a half an inch of rain in a short amount of time. This storm will remain over mainly rural areas of east central Park County, including the following locations... Cody Yellowstone Regional Airport. 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. && LAT...LON 4442 10908 4457 10916 4463 10894 4447 10887 TIME...MOT...LOC 2139Z 246DEG 3KT 4452 10903 21
The Riverton/Lander radar (KRIW), 63 km away, was scanning. The volume nearest the first event began at 21:52 UTC.
1 hail, 1 flash flood, 1 thunderstorm wind. Local standard time, as filed.
Up to ping pong ball size hail fell near Moneta. A man reported his truck was damaged by the falling hail.
Over an inch of rain along with small hail fell in Worland in only 25 minutes and brought street flooding. The water closed some streets for a while and water also backed into some buildings, including the city shop.
A 62 mph wind gust was reported near Linch, Wyoming.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2019Every state in 2019This day in weather historyWarnings in Wyoming, August 2019
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: 849801, 849803, 849802.