Warm moist air in an unstable environment and strong daytime heating allowed for the development of some strong to severe thunderstorms across southern Montana and northern Wyoming. One of these storms became severe as it moved northeastward through eastern Montana.
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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 GGW wrote it up.
Warm moist air in an unstable environment and strong daytime heating allowed for the development of some strong to severe thunderstorms across southern Montana and northern Wyoming. One of these storms became severe as it moved northeastward through eastern Montana.
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 Glasgow, MT wrote its last area forecast discussion before the first event at May 31, 2:15 PM MST, 3 hours 35 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 315 PM MDT Sun May 31 2020 .DISCUSSION... The main forecast issues in the coming week are the storms for this evening, the next chance of rain Monday night and Tuesday, then storm chances late week into the coming weekend. Throughout the forecast period, temperatures will be above seasonal averages. Short term (tonight and Monday)... As of 2:50 pm MDT, a cold front was beginning to move into the western part of the CWA. Behind it, temperatures and dew points have dropped, with satellite showing a line of clouds from the northwest corner of Phillips County to Lodge Pole to War Horse Lake (in western Petroleum County). Temperatures have not warmed as much as previously forecast due to high clouds moving in this morning, which has tempered daytime heating. As a result, we're going to struggle to reach convective temperatures with what's left of the afternoon and into the early evening. There was a flareup of convection in southern Blaine County along that previously mentioned line of clouds, but it fell apart. There is some room for convective development ahead of that line of clouds and the back edge of the high clouds (which extend from about Thoeny to Fort Peck to the Flowing Wells Rest Area, where temperatures are in the upper 80s and lower 90s (Malta is 91, for example). There's also plenty of moisture, with widespread dew points in the 60s in the eastern side of the CWA (the moist spots for dew points include Glendive and Terry, both at 64). The prime time for any development will be before 9pm (3z), with any storms moving into North Dakota (and out of our area) after that. Tomorrow will be cooler than today, but still above seasonal normals for temperatures. Medium term (Monday night through Thursday)... Upper level ridging will be the primary driver of weather for much of this week. A disturbance will ride the ridge tomorrow night into Tuesday and bring a chance of showers and thunderstorms to the area before moving out. After that moves out, it dries out once again. Long term (Friday and beyond)... The upper ridge will begin to break down late in the week as an upper level trough begins to flatten the ridge. Underneath it at the surface, an area of low pressure begins to develop as well. This far out, models suggest an increase in wind and an increase in shower/thunderstorm chances, and couldn't rule out some severe storms but it's still early to determine that with any certainty. 97 && .AVIATION... FLIGHT CONDITIONS: VFR, with brief periods of MVFR or IFR visibilities during thunderstorms. WINDS: S 15-25 kts through this afternoon, becoming W at KGGW late this afternoon with frontal passage. Winds become W 10-20 kts at KGGW & KOLF early this evening, and W 5-15 kts at KSDY & KGDV by the late evening. Monday's winds are expected to be NW 5-15 kts. DISCUSSION: A few thunderstorms are expected to develop later this afternoon between KGGW & KOLF and between KJDN & KGDV, then track eastward through the evening and be over or near KGDV & KSDY through the evening. Although there not many are expected, any that do develop will be capable of producing strong winds and hail. After frontal passage, LLWS is possible at any TAF site, but seems to be most likely at KGGW & KGDV. 97 && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Lake Wind Advisory until 9 PM MDT this evening For Fort Peck Lake for Central and Southeast Phillips...Central and Southern Valley...Garfield...McCone...Petroleum. && weather.gov/glasgow
Special Weather Statement
National Weather Service Glasgow MT
249 PM MDT Sun May 31 2020
MTZ016-017-059-061-312130-
Central and Southeast Phillips MT-Northern Valley MT-
Northern Phillips MT-Central and Southern Valley MT-
249 PM MDT Sun May 31 2020
...SPECIAL WEATHER STATEMENT...
At 247 PM MDT, Doppler radar was tracking a thunderstorm with strong
wind gusts along a line extending from 7 miles south of Loring to 21
miles northeast of Zortman. Movement was northeast at 45 mph.
Winds in excess of 40 mph will be possible with these storms. A wind
gust to 50 mph occurred in Havre with this system.
Locations impacted include...
Malta, Whitewater, Saco, Hinsdale, Thoeny, Sleeping Buffalo,
Frenchman Reservoir and Bowdoin.
LAT...LON 4900 10678 4824 10709 4800 10817 4874 10788
4900 10709
TIME...MOT...LOC 2047Z 246DEG 48KT 4868 10790 4808 10813
NWS GlasgowSpecial Weather Statement National Weather Service Glasgow MT 346 PM MDT Sun May 31 2020 MTZ016-312230- Central and Southeast Phillips MT- 346 PM MDT Sun May 31 2020 ...SIGNIFICANT WEATHER ADVISORY FOR EAST CENTRAL PHILLIPS COUNTY UNTIL 430 PM MDT... At 345 PM MDT, Doppler radar was tracking a strong thunderstorm 19 miles south of Malta, moving northeast at 30 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 east central Phillips 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 4795 10790 4809 10808 4841 10770 4818 10741 TIME...MOT...LOC 2145Z 228DEG 28KT 4808 10791 NWS Glasgow
Special Weather Statement National Weather Service Glasgow MT 613 PM MDT Sun May 31 2020 MTZ017-022-023-010115- Garfield MT-McCone MT-Central and Southern Valley MT- 613 PM MDT Sun May 31 2020 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN GARFIELD...SOUTHERN VALLEY AND NORTHWESTERN MCCONE COUNTIES UNTIL 715 PM MDT... At 612 PM MDT, Doppler radar was tracking a strong thunderstorm 11 miles east of Hell Creek Rec Area, or 23 miles northeast of Jordan, moving northeast at 25 mph. Wind gusts of 50 to 55 mph will be possible with this storm. Locations impacted include... Nelson Creek Rec Area, Rock Creek Rec Area and Haxby. PRECAUTIONARY/PREPAREDNESS ACTIONS... If on or near Fort Peck Lake, get out of the water and move indoors or inside a vehicle. Remember, lightning can strike out to 10 miles from the parent thunderstorm. If you can hear thunder, you are close enough to be struck by lightning. Move to safe shelter now! Do not be caught on the water in a thunderstorm. Persons in campgrounds should consider seeking sturdy shelter until this storm passes. && LAT...LON 4749 10667 4764 10681 4803 10632 4750 10589 TIME...MOT...LOC 0012Z 237DEG 21KT 4761 10665 GAH
The Glasgow radar (KGGW), 78 km away, was scanning. The volume nearest the first event began at 00:47 UTC.
1 thunderstorm wind. Local standard time, as filed.
Public estimated 60 mph wind gusts at the Nelson Creek Recreation Area. Time estimated from radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2020Every state in 2020This day in weather historyWarnings in Montana, May 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: 886991.