Thunderstorms developed ahead of a shortwave and a couple became severe. Wind gusts of over 58 mph were recorded in Fremont and Natrona Counties, with the strongest wind gust of 67 mph at Red Canyon.
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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.
Thunderstorms developed ahead of a shortwave and a couple became severe. Wind gusts of over 58 mph were recorded in Fremont and Natrona Counties, with the strongest wind gust of 67 mph at Red Canyon.
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 7, 12:53 PM MST, 43 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 153 PM MDT Sun Jun 7 2020 .SHORT TERM...Rest of Today through Monday Night Issued at 153 PM MDT Sun Jun 7 2020 The prominent circulation now appears to be over the Nevada/Oregon border. This low will track to central Idaho tonight and then just to the north of Yellowstone National Park by Monday morning. This weather system and all its components will make for an active couple of days weather wise with varied weather phenomena. A batch of PVA riding toward the northeast around the broad circulation around the low will track across the CWA during the balance of the day today. There is already a line of showers and thunderstorms that has been occurring in the far west and southwest along with snow in the mountains above 9000 feet. Kemmerer around 7000 feet has had snow as well. Thunderstorms are already becoming strong in northeast Utah. At the time of this writing, it has already been snowing and accumulating at Togwotee Lodge as colder has seeped in behind yesterday's lead shortwave with colder air on the way. These showers and afternoon thunderstorms will take most of the day today to track southwest to northeast across the CWA. Lifted indices will be widespread -2 and -3 across the area today. The only significant CAPE appears to be in northeast Johnson County. With 45 mph southwest winds at 700mb progged for today, mostly in the south and east zones, this matches up with where SPC has put us in a slight risk. So, today's convection could mimic the activity that occurred yesterday with weak convective cells capable of potentially damaging wind gusts. We should also see some small hail given the descending freezing levels and wet bulb zeros. Not as much rain will fall today out of these cells with PWs a little over a half inch as compared to yesterdays inch. With that said, and the fast speeds of any convective cells, flooding will probably not be an issue, unless the areas that received 0.75 to 1.00 inches of precip yesterday receive more locally heavy rain today. Most of the precip will likely occur in the west where dynamics more directly associated with the QG forcing from the aforementioned synoptic weather feature will take place. As for river flooding, creeks and rivers on the east slope of the southern Wind River Mountains responded to heavy rainfall and flirted with action stages, but now seem to be receding. Any added rainfall will coincide with falling temperatures so, right now, river flooding is not a big concern. There will be another batch of precip moving southwest to northeast early this evening associated with the next batch of PVA. Then there will be a lull in the precip for a few hours before more rain and snow moves into the west from the northwest from the actual trough passage as the low tracks from central Idaho to just north of Yellowstone National Park. This precip will follow the trailing trough passage and associated strong katafront marking the leading edge of the much colder air nosing into Wyoming from the west on the backside of the low. Sharp surface pressure rises of 8mb in these hours will accompany the front east of the Divide, so most of these areas should see a blast of wind at some point this evening. Monday morning looks to be the apex of the anticipated snow event across mostly the western mountains, with 700mb temps dropping close to minus 8C which will easily drop snow levels down to the valley floors in the far west by 12Z Monday. Hence the winter weather advisory in effect there for tonight and Monday morning in the western mtns. Less precip will fall east of the Divide with snow levels dropping to 6K, so even foothill locations could see some white stuff Monday morning as well as Sweetwater County. It looks like there could even be a brief period of wrap around isentropic lift in the northwest to help snowfall along. On Monday, numerous rain and snow showers will continue in the west ahead of another shortwave in the northwest flow, not directly associated with the main low. Then as a flat ridge builds into the area and the northwest flow becomes more confluent, the rain and snow showers will diminish in the northwest and west. By 12Z Tuesday, many areas could see freezing temps. We already upgraded the freeze watch to wa warning for tonight through Monday morning across the west and south as well as Dubois. .LONG TERM...Tuesday through Sunday Issued at 153 PM MDT Sun Jun 7 2020 Tuesday will dawn generally clear given widespread downward forcing in the wake of a shortwave. This will mean a cool start to the day and high temperatures will not reach seasonal normals. However, it will be the start of a warming trend. Trough axis will gradually swing to our east during the day with 100kt jet streak overhead in northwest flow aloft. Given this pattern, believe there could still be lingering convection Tuesday afternoon across the north and east. Ridge then begins to build to our west Wednesday which should limit the influx of moisture and allow for continued warming temperatures. Isolated convection cannot be ruled out across the northwest corner given northwest flow aloft even with limited moisture. The ridge will amplify more Thursday and traverse the forecast area Friday in response to a digging trough along the West Coast. This trough and closed low will transition onshore into the Pacific Northwest Friday, shifting the ridge axis to our east Friday. This will open up the state to warm, southerly flow aloft. The heat will return as 700mb temperatures climb to +14 to +17C. These temperatures combined with a dry atmosphere and gusty southerly wind will elevate fire weather concerns across at least southwest Wyoming Friday afternoon. Saturday is likely to find areas east of the Continental Divide in a similar to pattern to that of Friday given the slow-moving nature of the closed low. Saturday will remain warm and windy across the east. The far west should see slightly cooler temperatures as the low trudges east. Jet streak is projected to eject northeast across Idaho Saturday, which could provide the impetus for a more active round of convection. This is a long ways off and there could be dry slotting and limited moisture over the west Saturday afternoon, but this does bear watching. While in good agreement through about Saturday, medium-range forecast models diverge Sunday. ECMWF splits the energy to our north and south, while the GFS wants to spin the closed low north into Montana. Either way, it should at least be cooler Sunday with the best chance of showers in the west and northwest. && .AVIATION...(For the 18Z TAFS through 18Z Monday) Issued at 1130 AM MDT Sun Jun 7 2020 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Showers already ongoing across the far west will become more widespread with more showers and thunderstorms erupting and moving east between 18Z-22Z/Sunday. Gusty outflow wind of 35-45kts possible with the strongest convection as well as localized MVFR and even brief IFR. Passage of a cold front will swing the gusty west to southwest surface wind to the west-northwest through the afternoon except at KJAC. KJAC will be in and out of MVFR and VFR through the afternoon. Convection looks to wind down around 03Z/Monday with a brief respite. Expect MVFR and light snow at KJAC beginning around 11Z-14Z/Monday. Other terminals will be VFR after 03Z/Monday. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals Showers and thunderstorms will increase in coverage and intensity after 20Z/Sunday. Strongest convection expected between about 21Z/Sunday and 01Z/Monday with localized outflow wind 35-45kts and MVFR conditions. Gusty west-southwest surface wind will veer toward the west-northwest and continue through Sunday evening. All terminals will be VFR and precipitation-free by 06Z/Sunday, although jet max aloft could aid lingering showers in central Wyoming through the night. Westerly wind will increase again late Monday morning at the central terminals. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued AT 153 PM MDT Sun Jun 7 2020 A large area of low pressure will slowly traverse the forecast area Sunday and Monday. Cooler temperatures will filter into the region behind a cold front pushing east Sunday afternoon and evening. Gusty west-northwest wind will occur behind this cold front. Scattered showers and thunderstorms will gradually decrease in coverage and intensity Sunday evening. However, isolated light showers may continue overnight in the Casper Dispatch area. The low pressure system will slowly pinwheel east on Monday with the backside set to rotate an area of precipitation through the region beginning in the west Monday morning. Accumulating mountain snow will occur along and west of the Continental Divide. The precipitation will spread east of the Divide Monday afternoon, but it will be in the form of scattered rain showers and isolated thunderstorms. The best chance for these showers and storms will be across the Cody Dispatch area. Gusty west to northwest wind is anticipated as the low pressure area spins east of the forecast area. Clearing and drying conditions arrive Monday night with widespread low temperatures in the 30s. It will be drier Tuesday along with a breezy west-northwest wind. Overall, the trend will be toward drier and warmer conditions Tuesday through the end of the week as a ridge of high pressure builds over western Wyoming by Thursday. Smoke dispersal will be best across the Casper Dispatch area each afternoon. && .RIW WATCHES/WARNINGS/ADVISORIES... Freeze Warning from 3 AM to 9 AM MDT Monday for WYZ013-016-023- 025>030. Winter Weather Advisory from 11 PM this evening to noon MDT Monday for WYZ001-012. && SHORT TERM...Lipson LONG TERM...CNJ AVIATION...CNJ FIRE WEATHER...CNJ
Hazardous Weather Outlook National Weather Service Riverton WY 1115 AM MDT Sun Jun 7 2020 WYZ001>020-022>030-081300- 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- 1115 AM MDT Sun Jun 7 2020 ...A Slight Risk of Severe Thunderstorms Today for Portions of Southern and Central Wyoming... ...Winter Weather Advisory for Teton and Gros Ventre Mountains and Yellowstone Tonight and Monday Morning... ...Freeze Warning Tonight for the lower elevations of Western Wyoming... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Rest of Today and Tonight Showers and thunderstorms will become widespread this afternoon and evening. Some of the thunderstorms could be severe east of a line from around Kemmerer to Riverton to Greybull. The main hazard will be damaging winds. Attention then turns to northwest Wyoming where accumulating snow will fall in the western mountains mainly tonight into Monday morning. The most significant impacts will be across the Teton and Gros Ventre Mountains as well as Yellowstone National Park. Low temperatures will drop below freezing in the lower elevations of western Wyoming tonight. .DAYS TWO THROUGH SEVEN...Monday through Saturday Monday...Isolated to scattered showers and thunderstorms. Higher elevation snow gradually ends in most locations by Monday night. Friday and Saturday...Above normal temperatures, gusty southwest wind, and low relative humidity could lead to elevated fire weather conditions across southwest and central Wyoming. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions, especially wind gusts and wind damage.
Special Weather Statement
National Weather Service Riverton WY
127 PM MDT Sun Jun 7 2020
WYZ014-019-026-028-072015-
Wind River Mountains West-Upper Green River Basin-Green Mountains and
Rattlesnake Range-Rock Springs and Green River-
127 PM MDT Sun Jun 7 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SUBLETTE...SOUTH
CENTRAL FREMONT AND NORTHWESTERN SWEETWATER COUNTIES UNTIL 215 PM
MDT...
At 126 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles southeast of Eden, which is 11 miles south of Farson, moving
northeast at 40 to 50 mph.
Wind gusts of 45 to 55 mph will be possible with this storm. Heavy
rain and a brief period of pea sized hail may also occur.
This strong thunderstorm will be near...
Eden around 130 PM MDT.
Killpecker Dune Field and Boars Tusk around 135 PM MDT.
South Pass Rest Area around 210 PM MDT.
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 4199 10967 4247 10923 4234 10854 4193 10892
4187 10907 4188 10914 4183 10918
TIME...MOT...LOC 1926Z 209DEG 44KT 4195 10937
CNJSpecial Weather Statement National Weather Service Riverton WY 135 PM MDT Sun Jun 7 2020 WYZ014-015-081000- Wind River Mountains West-Wind River Mountains East- 135 PM MDT Sun Jun 7 2020 This is a special weather statement from the National Weather Service in Riverton. * WHAT...Periods of snow. * WHERE...Wind River Mountains. * SNOW AMOUNTS...3 to 5 inches over Union Pass, but little or no snow across South Pass. * WHEN...Tonight and Monday. * ADDITIONAL DETAILS...Campers and hikers will need to prepare for sharply colder temperatures and winter like conditions. WYZ024-081000- Salt River and Wyoming Ranges- 135 PM MDT Sun Jun 7 2020 This is a special weather statement from the National Weather Service in Riverton. * WHAT...Periods of snow. Total snowfall of 2 to 5 inches above 7500 feet. * WHERE...Salt River and Wyoming Ranges. * WHEN...Tonight and Monday. * ADDITIONAL DETAILS...Campers and hikers will need to prepare for sharply colder temperatures and winter like conditions. WYZ002-081000- Absaroka Mountains- 135 PM MDT Sun Jun 7 2020 This is a special weather statement from the National Weather Service in Riverton. * WHAT...Periods of snow. * WHERE...Absaroka Mountains. * SNOW AMOUNTS...2 to 4 inches over the west including Pahaska, but little or none over the far east. * WHEN...Tonight and Monday. * ADDITIONAL DETAILS...Campers and hikers will need to prepare for sharply colder temperatures and winter like conditions.
Special Weather Statement
National Weather Service Riverton WY
152 PM MDT Sun Jun 7 2020
WYZ017-019-072045-
Wind River Basin-Green Mountains and Rattlesnake Range-
152 PM MDT Sun Jun 7 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN NATRONA AND
SOUTHEASTERN FREMONT COUNTIES UNTIL 245 PM MDT...
At 151 PM MDT, Doppler radar was tracking a thunderstorm 9
miles west of Crooks Gap, which is 11 miles southwest of Jeffrey
City, moving northeast at 55 mph.
Pea size hail and winds in excess of 40 to 50 mph will be possible with
this storm.
This strong thunderstorm will be near...
Jeffrey City around 205 PM MDT.
Castle Gardens around 235 PM MDT.
Ervay around 240 PM MDT.
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 4222 10807 4223 10811 4221 10815 4229 10829
4307 10798 4270 10690
TIME...MOT...LOC 1951Z 220DEG 49KT 4242 10802
LipsonSpecial Weather Statement
National Weather Service Riverton WY
211 PM MDT Sun Jun 7 2020
WYZ014-015-017>019-072100-
Wind River Mountains West-Wind River Basin-Wind River Mountains
East-Green Mountains and Rattlesnake Range-Lander Foothills-
211 PM MDT Sun Jun 7 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SUBLETTE AND
SOUTHEASTERN FREMONT COUNTIES UNTIL 300 PM MDT...
At 209 PM MDT, Doppler radar was tracking strong thunderstorms
between Oregon Buttes and Farson, moving northeast at 50 mph.
Pea size hail, brief heavy rain, and wind gusts of 45 to 55 mph will
be possible with these storms. Reports of wind gusts to 50 mph were
received from Farson when the storm passed nearby.
This strong thunderstorm will be near...
South Pass City around 230 PM MDT.
Fiddlers Lake, Louis Lake, Christina Lake and Upper Silas Lake
around 240 PM MDT.
Worthen Meadows Reservoir around 245 PM MDT.
Frye Lake around 250 PM MDT.
Sinks Canyon State Park around 255 PM MDT.
Lander and Milford around 300 PM MDT.
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 4243 10913 4245 10915 4244 10916 4245 10917
4247 10918 4248 10921 4247 10921 4247 10923
4304 10890 4288 10805 4229 10829
TIME...MOT...LOC 2008Z 203DEG 42KT 4227 10908
CNJSpecial Weather Statement
National Weather Service Riverton WY
222 PM MDT Sun Jun 7 2020
WYZ014-019-026-030-072100-
Wind River Mountains West-East Sweetwater County-Upper Green River
Basin-Green Mountains and Rattlesnake Range-
222 PM MDT Sun Jun 7 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SUBLETTE...SOUTH
CENTRAL FREMONT AND NORTH CENTRAL SWEETWATER COUNTIES UNTIL 300 PM
MDT...
At 221 PM MDT, Doppler radar was tracking a strong thunderstorm 16
miles south of Oregon Buttes, which is 34 miles east of Farson,
moving northeast at 50 mph. Other strong thunderstorms were rumbling
across central and northern Sweetwater County.
Wind gusts of 45 to 55 mph, pea sized, and brief heavy rain will be
possible with these storms. Gusts to around 55 mph have been
observed at near Rock Springs.
These storms will impact I-80 between the exit for Southwest Wyoming
Regional Airport and Bitter Creek. This includes Interstate 80
between mile markers 110 and 147.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
These storms 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 4158 10916 4184 10917 4187 10914 4193 10913
4201 10918 4249 10921 4223 10804 4147 10860
TIME...MOT...LOC 2019Z 204DEG 54KT 4203 10879
CNJSpecial Weather Statement
National Weather Service Riverton WY
225 PM MDT Sun Jun 7 2020
WYZ007-009-017>020-072130-
Owl Creek and Bridger Mountains-Wind River Basin-Bighorn Mountains
Southeast-Green Mountains and Rattlesnake Range-Natrona County Lower
Elevations-Lander Foothills-
225 PM MDT Sun Jun 7 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN NATRONA AND
SOUTHEASTERN FREMONT COUNTIES UNTIL 330 PM MDT...
At 224 PM MDT, Doppler radar was tracking a thunderstorm 9
miles southwest of Castle Gardens, which is 22 miles north of Jeffrey
City, moving northeast at 55 mph.
Pea size hail and winds in excess of 40 to 50 mph will be possible with
this storm.
This strong thunderstorm will be near...
Castle Gardens around 235 PM MDT.
Hiland around 255 PM MDT.
Other locations impacted by this storm include Natrona and Arminto.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Occasional 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 4221 10808 4223 10809 4223 10811 4220 10821
4232 10866 4344 10738 4302 10667
TIME...MOT...LOC 2024Z 212DEG 47KT 4281 10772
LipsonThe Riverton/Lander radar (KRIW), 51 km away, was scanning. The volume nearest the first event began at 20:36 UTC.
2 thunderstorm wind. Local standard time, as filed.
The wind sensor at Red Canyon had a maximum wind gust of 67 mph.
A 58 mph wind gust was reported at the Natrona County Airport. At Hat Six Road in Casper, Wyoming, the maximum wind gust was 60 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2020Every state in 2020This day in weather historyWarnings in Wyoming, June 2020
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: 898308, 898309.