A mildly unstable atmosphere combined with an approaching low pressure trough from the west to set off strong thunderstorms, some of which eventually spread severe wind gusts across portions of northeast Montana.
Every event with a place to put it. Tap one for its entry below.
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 mildly unstable atmosphere combined with an approaching low pressure trough from the west to set off strong thunderstorms, some of which eventually spread severe wind gusts across portions of northeast 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 Aug 20, 6:29 PM MST, 12 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 729 PM MDT Thu Aug 20 2020 .DISCUSSION... Evening update... Main change was to tweak the POPs to time the storms just now (as of 7:15 pm) crossing the border into Phillips and Petroleum Counties. Will need to monitor for fire starts from lightning strikes from this line as well as the gusty winds associated with it. Tomorrow will still be hot, but not as hot as the last few days. 97 Previous discussion... Afternoon Update: Storms have fired quite a bit earlier than was expected this morning, with lightning producing cells already in Phillips and Valley Counties. Few of the high resolution models have accurately depicted this trend, though some of the short term ensembles have had the closest forecast thus far. The atmospheric modification due to these early storms certainly could have an effect on coverage and intensity later on this evening and tonight, but exactly how that will happen is of yet unknown. In the longer term, most of the forecast remains the same, though further drying out of the surface is expected tomorrow as was thought to end up being the case. Thus, fire weather for most of tomorrow, as opposed to just through the morning, may need to be monitored. Cliff PREVIOUS DISCUSSION: Another hot and dry weather day is expected for NE Montana, though afternoon highs will be a couple of degrees shy of the previous few days. Thus, will not be issuing a Heat Advisory for today. That said, those who are sensitive to the heat should continue to follow heat safety measures such as staying hydrated and minimizing outdoor activities during the hours of peak heating. Thunderstorms will push into the area this evening with a lightning risk and gusty winds. SPC has maintained a Marginal Risk for severe thunderstorms, again further underscoring the wind threat. A new upper ridge pattern looks to unfold for Friday and Saturday, leading to warm and dry conditions once again across the CWA. High temperatures by Saturday may yet again soar into the upper 90s to near 100 degrees. Consensus blends were generally used to populate the forecast beyond the upcoming weekend given increasing spread in ensemble member guidance. && .AVIATION... Expected Flight Category: VFR Synopsis: Showers and some thunderstorms will push through the region tonight through Friday morning as a weak front moves through. Once the storms exit the region Friday, dry and hot conditions return. Ceilings, even under storms tonight, should remain in VFR territory with how dry conditions have been. Winds: Winds will typically be variable and under 10 kts through Friday morning, then pick up to around 10-20 kts out of the west to northwest by midday on Friday. However, underneath showers and storms tonight through Friday morning, expect winds to be variable but could be strong. Cliff && .FIRE WEATHER... Hot and dry conditions continue trough this evening. These dry conditions are going to precede increasing coverage of showers and thunderstorms tonight and through Friday morning. There is a good chance that the region could see isolated to scattered dry lightning with conditions as they are right now. This has led to the decision to consider the overnight hours as critical for fire weather concerns due to the potential for dry lightning, and the fact that the main risk factor from these thunderstorms in general will be strong gusty winds that could reach 50 mph. For fire weather, the combination of these two factors is the impetus for the critical conditions. On Friday, conditions on their own right will be elevated with fairly low RH values and winds of 10-20 mph sustained out of the west for much of the day, but when combined with the potential for dry lightning starts overnight, there is added concern for the ease of fire spread on Friday, thus conditions should be closely monitored for potential expansion of critical conditions trough a longer portion of the day Friday. Cliff && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 6 AM MDT Friday for MTZ120-122-134>137. && weather.gov/glasgow
Special Weather Statement
National Weather Service Glasgow MT
710 PM MDT Thu Aug 20 2020
MTZ016-021-022-059-060-210215-
Petroleum MT-Garfield MT-Southwest Phillips MT-
Central and Southeast Phillips MT-Northern Phillips MT-
710 PM MDT Thu Aug 20 2020
...SIGNIFICANT WEATHER ADVISORY FOR PHILLIPS...SOUTHWESTERN GARFIELD
AND PETROLEUM COUNTIES UNTIL 815 PM MDT...
At 709 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 11 miles northeast of Harlem to 7 miles
southwest of Winnett. Movement was east at 45 mph.
Pea size hail and wind gusts up to 50 mph will be possible with these
storms.
Locations impacted include...
Malta, Winnett, Zortman, Dodson, Fourchette, U L Bend Rec Area,
Crooked Creek Rec Area, Flatwillow, Devils Creek Rec Area, Mosby,
Phillips, Petrolia Lake, Wagner, Fred Robinson Bridge, Tiegen,
Landusky, Content, Sun Prairie, Bowdoin and Cat Creek.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
These storms may intensify, so be certain to monitor local radio
stations and available television NWS Glasgowstations for additional
information and possible warnings from the National Weather Service.
&&
LAT...LON 4792 10889 4792 10863 4799 10861 4798 10843
4845 10841 4843 10836 4874 10832 4874 10758
4685 10748 4685 10789 4677 10784 4675 10863
4710 10861 4710 10874 4727 10872 4732 10831
4758 10831 4764 10877 4773 10889
TIME...MOT...LOC 0109Z 248DEG 37KT 4864 10860 4695 10848
GAHPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
741 PM MDT THU AUG 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0732 PM TSTM WND GST 1 ESE ZORTMAN 47.91N 108.50W
08/20/2020 M55 MPH PHILLIPS MT OTHER FEDERAL
ZORTMAN BLM RAWS.
&&
TEDJThe Glasgow radar (KGGW), 149 km away, was scanning. The volume nearest the first event began at 01:40 UTC.
14 thunderstorm wind. Local standard time, as filed.
At the Manning Corral Dogtown RAWS site (MCDM8), a 60 mph gust was recorded.
At the Malta South US-191 DOT site (MTMAL), Multiple wind gusts of 66 mph were recorded from 18:45 MST to 18:59 MST.
At the Zortman BLM RAWS site (ALDM8), a 64 mph wind gust was recorded sometime between 18:32 MST and 19:32 MST.
At the Malta airport AWOS site (KM75), a 64 mph wind gust was recorded.
At the Jordan airport ASOS site (KJDN), a 68 mph wind gust was recorded.
At the Saco US-2 DOT site (MTSCO), a 62 mph wind gust was recorded.
At the South Sawmill Creek RAWS site (SSMM8), a 59 mph wind gust was recorded.
A CoCoRaHS observer 2 NNW Glasgow estimated a 65 mph wind gust.
At the Glasgow airport ASOS site (KGGW), a 67 mph wind gust was recorded.
Public measured a 62 mph wind gust.
At the Glasgow airport ASOS site (KGGW), a 58 mph wind gust was recorded.
At the King Coulee RAWS site (KIGM8), a 64 mph wind gust was recorded.
At the Saint Marie MARCO site (07MT), a 62 mph wind gust was recorded.
At the Circle Town County airport mesonet site (K4U6), a 58 mph wind gust was recorded.
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, August 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: 912854, 912845, 912849, 912848, 912837, 912851, 912855, 912865, 912847, 912867, 912857, 912850, 912853, 912856.