A focused area of favorable moisture and winds combined with a marginally unstable atmosphere to sustain one severe thunderstorm which moved through far 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.
A focused area of favorable moisture and winds combined with a marginally unstable atmosphere to sustain one severe thunderstorm which moved through far 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 Jul 20, 3:33 PM MST, 37 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 433 PM MDT Tue Jul 20 2021 .DISCUSSION... Low pressure system and cold front is moving east through eastern Montana this afternoon. Meanwhile, a shortwave trough is moving through the area this afternoon and evening. The system is bringing isolated to scattered showers and thunderstorms to eastern Montana this afternoon and evening. Skies clear late tonight and upper ridge builds back into the area during the day on Wednesday. With more sun expected, most areas will be in the 90s for highs with a few places near 100. Ridge moves to the east Wednesday Night and a wave in SW flow aloft could bring a chance of thunderstorms to the western half of the region. Thursday will be a hot day ahead of a cold front Thursday evening. Many areas will have highs near 100. While the heat risk is expected to be lower for most of the region on Wednesday, the heat risk returns for Thursday Will keep the Excessive Heat Warning in effect for most the region. The exception will be the zones along the Canadian border where temperatures are expected to remain mostly below 100 for the rest of the week. The cold front will bring a chance of thunderstorms Thursday afternoon and night. A more zonal flow aloft is expected starting on Friday and continuing through early next week. The waves in the flow aloft will stay up north in Canada which will give NE Montana mainly dry weather with highs in the 90s in most areas. && .AVIATION... LAST UPDATED: 2230Z FLIGHT CAT: VFR. LLWS: Low level Wind Shear will be possible from 04-09Z at KSDY and maybe KGDV. Only 1 to 2 hours are currently in the TAF, but on closer inspection LLWS may be able to last a little longer or impact KGDV as well. this has much lower confidence. DISCUSSION: With low pressure along with monsoonal moisture through tonight will allow isolated to scattered showers to pass through the area. Skies will start to clear around midnight with dry conditions through Wednesday. SMOKE AND HAZE: Will continue to push through the area over the next few days, lowering normal and slantwise visibility at times. Currently MVFR visibility is not anticipated. WIND: north to northeast at 5 to 10 kts through midnight. backing to north to northwest early Wednesday morning. Then increasing to 5 to 15 kts Wednesday afternoon. /GAH && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 9 PM MDT Thursday for Central and Southeast Phillips...Central and Southern Valley...Dawson... Eastern Roosevelt...Garfield...McCone...Petroleum...Prairie... Richland...Southwest Phillips...Western Roosevelt...Wibaux. && weather.gov/glasgow
Special Weather Statement National Weather Service Glasgow MT 451 PM MDT Tue Jul 20 2021 MTZ027-202315- Wibaux MT- 451 PM MDT Tue Jul 20 2021 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN WIBAUX COUNTY UNTIL 515 PM MDT... At 451 PM MDT, Doppler radar was tracking a strong thunderstorm near Carlyle, or 15 miles south of Beach, moving east at 20 mph. Pea size hail and wind gusts of 50 to 55 mph will be possible with this storm. Locations impacted include... Carlyle and Saint Phillip. 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. 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 4664 10414 4682 10423 4687 10404 4664 10405 TIME...MOT...LOC 2251Z 253DEG 17KT 4670 10405 NWS Glasgow
The Glasgow radar (KGGW), 243 km away, was scanning. The volume nearest the first event began at 23:08 UTC.
1 thunderstorm wind. Local standard time, as filed.
Public reported that chained down wind break panels were destroyed. A 1,000 gallon water tank was also destroyed. Wind speed was estimated to be 80mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2021Every state in 2021This day in weather historyWarnings in Montana, July 2021
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: 975298.