On August 30, a weak shower moved over Bozeman, MT, and collapsed in the very dry air mass near the surface. The resulting downburst winds were measured at 79 mph at the Belgrade Airport.
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The episode as NWS TFX wrote it up.
On August 30, a weak shower moved over Bozeman, MT, and collapsed in the very dry air mass near the surface. The resulting downburst winds were measured at 79 mph at the Belgrade Airport.
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 Great Falls, MT wrote its last area forecast discussion before the first event at Aug 30, 1:57 PM MST, 2 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 257 PM MDT Mon Aug 30 2021 .SYNOPSIS... An increasing southwest breeze will bring haze and wildfire smoke back into Southwest Montana. An isolated overnight light rain shower is possible near or east of the Havre area. Otherwise, mild, dry, and breezy conditions continue through Tuesday. Temperatures turn cooler on Wednesday following a dry cold front. This front will also help clear the haze and smoke from the region. && .DISCUSSION... Satellite imagery shows increasing wildfire smoke returning to Southwest Montana on the dry southwesterly flow aloft. Scattered cumulus are developing over mountain ridgetops. These most likely do not have enough moisture to develop into showers, but some of the latest CAM guidance carries a slight chance for light showers into north-central Montana overnight. Although excessively dry, there is a subtle upper level shortwave that may be able to support some of this activity. On Tuesday the southwesterly flow aloft strengthens with a deepening synoptic scale trough over the Pacific Northwest. Elevated to near-critical fire weather conditions develop Tuesday afternoon, especially over ridgetop areas exposed to the increasing mid-level winds and where humidity will remain low. Most areas on Tuesday afternoon should see minimum relative humidity drop well into the teens. A dry cold front works through the region on Tuesday, turning winds to west or northwest and increasing for a short time due to pressure rises behind the front. PN Wednesday through next Monday...The low pressure trough axis is forecast to generally remain over Alberta through the Pacific Northwest to off the California coast at least through the day on Thursday. This will keep the forecast area under the southwesterly flow aloft, which will keep a chance for showers and thunderstorms at times mainly over the area along and east of a Havre to Dillon line, but it will also keep temperatures below normal. Forecast models then diverge on solutions for Friday through the Labor Day holiday weekend, so will stay with the consensus solution of the National Blend of Models (NBM). This keeps a chance of showers and thunderstorms mainly over southwest Montana on Friday, likely due to a more westerly flow aloft returning to the area as weak high pressure ridging moves into the area. This ridging should help keep the area dry through Sunday, as temperatures warm back up to near normal with periods of breezy westerly winds. However, a weak low pressure trough will then cool temperatures a bit as it brings a chance for showers for Labor Day (Monday). -Coulston && .AVIATION... 1125 AM MDT Mon Aug 30 2021 (30/18Z TAF period) VFR conditions will continue through at least the next 24 hours. Visible satellite imagery shows dispersed wildfire smoke drifting towards SW Montana, but should not result in visibility restrictions below 8SM at area terminals. High clouds begin to develop later this afternoon and evening, particularly across SW Montana, with a slight chance for isolated light rain showers, mainly over mountain areas. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 49 82 42 74 / 0 0 10 0 CTB 48 72 39 68 / 0 0 0 0 HLN 52 83 46 76 / 0 0 0 0 BZN 47 86 42 76 / 0 0 0 0 WYS 33 76 35 72 / 0 0 0 10 DLN 45 82 39 76 / 0 0 0 0 HVR 53 83 46 74 / 10 0 20 0 LWT 51 83 46 72 / 10 10 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && http://www.weather.gov/greatfalls
The Great Falls radar (KTFX), 186 km away, was scanning. The volume nearest the first event began at 23:16 UTC.
1 thunderstorm wind. Local standard time, as filed.
Wind gust came from convective clouds with no lightning observed. KTFX/KBLX radars showed only 20 to 25 DBZ echoes.
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, August 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: 971538.