Severe thunderstorms developed over portions of central and southern Wyoming. In Sweetwater County, a tornado formed near Granger.
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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.
Severe thunderstorms developed over portions of central and southern Wyoming. In Sweetwater County, a tornado formed near Granger. The tornado was photographed by many people. The tornado remained over open country and caused no damage. In addition, flash flooding was reported over rural portions of Sweetwater County. In Fremont County, another tornado briefly touched down southeast of South Pass.
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 28, 1:35 PM MST, 25 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 235 PM MDT Mon May 28 2018 .SHORT TERM...(Tonight through Thursday) Several shortwaves within a broad trough across the Rockies and Great Basin have impacted the forecast area today. The first of these shortwaves is now in southeast Montana and rotating north. This movement has gradually shifted wrap-around moisture from Johnson County to the northern Big Horn Basin Monday afternoon. Steady rainfall of around a tenth of an inch has been common. This rain shield will continue to pull away from northern Wyoming by early this evening. Multiple rivers at our near bankfull or flood stage on either side of the Bighorn Mountains. Expect a general downward trend in river levels this evening with the flood threat gradually diminishing. To the south, a shortwave over eastern Utah will rotate north the remainder of Monday and Monday night. Storms have been firing over southern Sweetwater County and over the higher terrain of the southwest. Heavy rain and small hail likely to be the main hazards with some storms producing gusty outflow wind of 40-50 mph. The area of interest will gradually shift to Natrona County late this afternoon and evening. Main concern is likely to remain heavy rain and small hail. For the most part, convection should decrease in coverage and intensity by 9 PM Monday with only lingering light showers overnight. This shortwave continues to the northeast Tuesday with wrap-around precipitation most prevalent across the north. Still have scattered showers and storms in most areas Tuesday with better coverage in the mountains, but these will not be as strong as the past few days. Brief heavy rain to remain the primary hazard, mainly across north central Wyoming. Conditions dry from west-to-east Tuesday night and Wednesday with a warming trend beginning. There is a slight chance of late day showers and storms across far west Wyoming late Wednesday afternoon and evening. Similar conditions are anticipated Thursday with the northwest the most likely location for showers and storms. Warm, southwest flow will boost temperatures and wind speeds Thursday. Additional snowmelt is anticipated both days and heading into the weekend. .LONG TERM...(Thursday Night through Monday) A shortwave and associated Pacific cold front will move east across the area Friday. The timing of the passage of this feature has been waffling, but a daytime track through the forecast area looks plausible. Both the GFS and ECMWF solutions would indicate a chance for stronger thunderstorms, particularly across the north, as this shortwave sweeps east. It will turn cooler Friday from west-to-east in the wake of the cold front. A dry southwest flow will then reestablish over the area next weekend. Deterministic models show a sub-tropical low lifting from southern California into the area with southern Wyoming the most likely to see any impact in the Saturday night/Sunday timeframe. At this range, however, there could end up being substantial differences in track and timing so have continued to trend toward any notable effects from this system for this forecast package. && .AVIATION...For the 00Z TAFS through 00Z Wednesday West of the Continental Divide...KJAC/KBPI/KPNA/KRKS Expect scattered showers and thunderstorms over the area this afternoon and evening, mainly along and south of a line from KAFO to KPNA. The activity will decrease to isolated showers after 03Z/Tue. Local MVFR to IFR conditions will occur in thunderstorms which will obscure mountains at times. KJAC will see MVFR to IFR conditions in the area from 09Z through 16Z/Tue. Another round of showers and storms are expected Tuesday afternoon, mainly over the higher terrain. Otherwise, VFR conditions will prevail through the period. East of the Continental Divide...KCPR/KCOD/KRIW/KLND/KWRL Expect scattered showers and thunderstorms over the region this afternoon, primarily along and south of a line from KRIW to KCPR. The activity will decrease after 06Z/Tue. MVFR to IFR conditions will occur in thunderstorms which will obscure mountains at times. Another round of showers and storms are expected Tuesday afternoon, mainly along and north of a line from KCOD to KCPR and over the higher terrain. Otherwise, VFR conditions will prevail through the period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Several areas of low pressure will impact the regional weather picture through Tuesday. Overall, a broad area of low pressure to the south of Wyoming will gradually move to the northeast and across the state tonight and Tuesday. This will slowly shift the showers and thunderstorms away from the state by Tuesday night. Within this broad area of low pressure are other small disturbances, one of which has kept light rain across the far north much of Monday. This disturbance will pull northeast tonight and bring a gradual end to the rain in that region. Conditions will become drier from west-to-east Tuesday afternoon and evening. Wednesday and Thursday look primarily dry with with only a slight chance of showers and storms in the western mountains. It will also be warming Wednesday and Thursday with highs climbing to 10-15 degrees above normal by Thursday. These temperatures may get a further boost across the south and central areas Thursday as breezy southwest wind returns. && .RIW WATCHES/WARNINGS/ADVISORIES... Flood Watch until 6 PM MDT this evening for WYZ002>004-006-008- 009. && SHORT TERM...CNJ LONG TERM...Meunier/CNJ AVIATION...Hulme/CNJ FIRE WEATHER...CNJ
Hazardous Weather Outlook National Weather Service Riverton WY 309 AM MDT Mon May 28 2018 WYZ001>020-022>030-291100- 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- 309 AM MDT Mon May 28 2018 ...Flood Watch in effect through 6 PM MDT this evening for portions of Northern Wyoming east of the Continental Divide... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Scattered showers and thunderstorms developing over most of the area. Isolated severe thunderstorms possible in east central areas. Locally heavy rain may elevate the flood threat along rivers and creeks already running high from snowmelt. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday...Isolated to scattered showers and thunderstorms across the area. Thursday...Isolated to scattered showers and thunderstorms mainly in the north and west. .SPOTTER INFORMATION STATEMENT... Spotters are urged to report hail, wind gusts past 45 mph and any flooding. Thank you. TEAM RIVERTON
Special Weather Statement National Weather Service Riverton WY 124 PM MDT MON MAY 28 2018 WYZ029-030-282015- Flaming Gorge-East Sweetwater County- 124 PM MDT MON MAY 28 2018 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN SWEETWATER COUNTY UNTIL 215 PM MDT... At 122 PM MDT, Doppler radar was tracking a strong thunderstorm 27 miles east of Squaw Hollow Boat Ramp On Flaming Gorge, which is 36 miles south of Rock Springs, moving north at 10 mph. This storm will impact travel along Highway 191 South. 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 southwestern Sweetwater County. 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 4100 10924 4130 10950 4136 10895 4100 10892 TIME...MOT...LOC 1922Z 157DEG 10KT 4110 10904 Hulme
Special Weather Statement
National Weather Service Riverton WY
151 PM MDT MON MAY 28 2018
WYZ030-282030-
East Sweetwater County-
151 PM MDT MON MAY 28 2018
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SWEETWATER COUNTY
UNTIL 230 PM MDT...
At 151 PM MDT, Doppler radar was tracking a strong thunderstorm 11
miles west of Dad, which is 20 miles south of Wamsutter, moving west
at 20 mph.
Nickel size hail and winds in excess of 30 mph will be possible with
this storm.
This storm will remain over mainly rural areas OF southeastern
Sweetwater 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.
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 4120 10843 4162 10846 4156 10793 4140 10793
4140 10792 4133 10791 4120 10792
TIME...MOT...LOC 1951Z 093DEG 19KT 4138 10796
HulmeSpecial Weather Statement National Weather Service Riverton WY 216 PM MDT MON MAY 28 2018 WYZ030-282100- East Sweetwater County- 216 PM MDT MON MAY 28 2018 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTH CENTRAL SWEETWATER COUNTY UNTIL 300 PM MDT... At 215 PM MDT, Doppler radar was tracking a strong thunderstorm 25 miles south of Bitter Creek Rest Area, which is 38 miles southeast of Rock Springs, moving north at 10 mph. Dime size 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 Sweetwater County. 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 4120 10843 4120 10893 4146 10899 4150 10845 TIME...MOT...LOC 2015Z 171DEG 6KT 4127 10863 McDonald
Special Weather Statement
National Weather Service Riverton WY
228 PM MDT MON MAY 28 2018
WYZ030-282115-
East Sweetwater County-
228 PM MDT MON MAY 28 2018
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SWEETWATER COUNTY
UNTIL 315 PM MDT...
At 227 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles southeast of Table Rock, which is 19 miles southwest of
Wamsutter, moving west at 20 mph.
Nickel size hail and winds in excess of 30 mph will be possible with
this storm.
Locations impacted include...
Table Rock, Bitter Creek Rest Area, Patrick Draw Natural Gas
Processing Plant, Bitter Creek and Tipton.
This includes Interstate 80 between mile markers 137 and 165.
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 4120 10843 4149 10847 4148 10863 4164 10875
4173 10820 4139 10792 4118 10792
TIME...MOT...LOC 2027Z 107DEG 18KT 4151 10829
HulmeThe Riverton/Lander radar (KRIW), 84 km away, was scanning. The volume nearest the first event began at 21:02 UTC.
2 tornado, 1 flash flood. Local standard time, as filed.
A brief tornado was reported to the east of South Pass by the public. The tornado remained over open country and caused no damage.
Flooding was reported in rural eastern Sweetwater County. No damage was reported.
A tornado near Granger was well photographed by the general public and reported on local media. The tornado remained over open country and caused no damage.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2018Every state in 2018This day in weather historyThe tornado archive for Wyoming, 2018Warnings in Wyoming, May 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: 754012, 754011, 754010.