Strong winds from aloft were departing the region, but were able to remain over the Dawson/Wibaux County area just long enough with a favorable atmosphere that brought those winds down to the surface.
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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.
Strong winds from aloft were departing the region, but were able to remain over the Dawson/Wibaux County area just long enough with a favorable atmosphere that brought those winds down to the surface.
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 18, 2:13 AM MST, 6 hours 30 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 313 AM MDT Mon May 18 2020 .DISCUSSION... Synoptic Setup: A ridge of hot air runs from New Mexico up the high Plains of Colorado, Wyoming, eastern Montana and crests over southern Saskatchewan. Behind this A large trough sits over the coasts of northern California and the Pacific Northwest. In between a wide areas over southern to southwestern flow resides pulling in Pacific Moisture along with embedded shortwaves. Today through Tuesday: Ridge will remain in place due to a blocking pattern farther east. Afternoon showers and thunderstorms will develop over the central Montana mountains and trend north to northeast. These showers and isolated thunderstorms may impact the far eastern zones of Phillips and petroleum counties before moving up into Canada both afternoons. Tuesday looks a little more threatening with the showers making it about a county deeper into the CWA. At the same time PWs will begin rising across the east to about 1.0 inch. Wednesday to Wednesday night, ridge will begin moving east in the early morning as the large synoptic trough digs into the Four Corners. This will orient flow aloft from the south to almost southeast and allow a surface trough to begin forming in the CWA somewhere east of a line from Saco to Jordan and west of a line from Glendive to Poplar. An embedded shortwave and very strong shear of about 30 to 50 kts will combine with afternoon heating to form supercells along the surface trough. PWs will begin further moving upward to 1.2 to 1.4 inches east of the surface trough and feed these storms. The cells will move from south to north along the stationary trough from noon to nearly midnight. The training storms and near record high PWs lead to the conclusion of flash flooding being likely. Currently, the NAM, GFS, and EC all have a signal for the surface trough, high PWs, and training cells in a narrow corridor, but don't agree on exactly where this corridor will set up. This brings strong confidence in the event, but yet lacks an exact placement for impacts. Will give the day shift one more look, but right now flooding and large hail are the main impacts/considerations. Thursday to Sunday: flow will remain southwest bringing more chance for thunderstorms and showers. Highest chances look to be on Friday and Saturday. Sunday night onward: synoptic surface trough looks like it will move through during these periods lowering temperatures slightly and reducing chance for thunderstorms but not rain showers. GAH && .AVIATION... LLWS: Low level Winds Shear is possible at the terminals through 14Z this morning. FLIGHT CAT: VFR DISCUSSION: Scattered to broken mid to high clouds and dry through the TAF cycle. WIND: East to southeast this morning around 10 to 15 kts. Veering to the southeast to south and increasing to 15 to 20 kts with gusts up to 30 kts this afternoon. Calming to 10 to 20 kts this evening. GAH && .GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE. && weather.gov/glasgow
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
At the Beaver Hill I-94 DOT site (MTBVR), sustained winds of at least 40 mph began at 8:43 AM MST and continued at least each hour until 2:53 PM MST. Peak wind gusts of 60 mph were measured from 12:08 PM to 12:14 PM MST.
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: 881804.