Favorable wind shear and a weakly unstable atmosphere combined with an area of low pressure to produce a few strong thunderstorms, one of which brough severe downdraft winds to Garfield County.
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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.
Favorable wind shear and a weakly unstable atmosphere combined with an area of low pressure to produce a few strong thunderstorms, one of which brough severe downdraft winds to Garfield County.
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 25, 4:19 PM MST, 4 hours 13 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 519 PM MDT Tue Aug 25 2020 .DISCUSSION... Hot and dry weather conditions prevailed across Northeast Montana this afternoon. Some high level clouds streamed across the region, keeping some cloud coverage. High temperatures were again in the upper 90s across the area. A short wave trough will move quickly late tonight into the overnight hours, but most shower and thunderstorm activity will remain south of the region. However, one or two isolated strong thunderstorms can't be ruled out,mainly near Petroleum and Garfield Counties. Better chances for more widespread shower and thunderstorm activity is expected Wednesday and Thursday. At the end of the work week, Fire Weather concern increases as RH and winds reach critical values Late Thursday as a cold front moves across the region. For early next week, troughiness will result in markedly cooler temperatures. High temperatures are expected to be in the upper 60s to low 70s Monday and Tuesday next week. && .AVIATION... Updated 18:00pm (00Z 27-Aug) FLIGHT CATEGORY: VFR SYNOPSIS: A few isolated showers or thunderstorms will move through the area tonight and should exit the area by mid-morning. Haze from western wildfires continues to be an issue and could reduce visibilities at times down close to MVFR levels. Otherwise dry conditions prevail Wednesday until the evening hours when some more isolated to scattered thunderstorms move into the area. WINDS: NW to N winds 10-15 knots, becoming light and variable overnight, shifting to the W at 5 to 15 knots Wednesday afternoon. RMB && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch from Thursday afternoon through Thursday evening for MTZ134>137. && weather.gov/glasgow
Special Weather Statement
National Weather Service Glasgow MT
803 PM MDT Tue Aug 25 2020
MTZ016-021-022-060-260245-
Petroleum MT-Garfield MT-Southwest Phillips MT-
Central and Southeast Phillips MT-
803 PM MDT Tue Aug 25 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN PHILLIPS...
SOUTHWESTERN GARFIELD AND PETROLEUM COUNTIES UNTIL 845 PM MDT...
At 801 PM MDT, Doppler radar was tracking a line of showers and
thunderstorms along a line extending from near Fourchette to 8 miles
southeast of Flatwillow. Movement was east at 30 mph.
Winds in excess of 40 mph will be possible with these storms.
Locations impacted include...
Sand Springs, Fourchette, Devils Creek Rec Area, U L Bend Rec Area,
Edwards, Mosby, Crooked Creek Rec Area, Petrolia Lake, Sun Prairie,
Steve Fork and Cat Creek.
LAT...LON 4676 10831 4731 10837 4732 10831 4758 10831
4757 10834 4760 10840 4785 10845 4790 10754
4686 10697 4685 10789 4680 10784
TIME...MOT...LOC 0201Z 266DEG 45KT 4769 10798 4679 10824
NWS GlasgowPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
923 PM MDT TUE AUG 25 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0907 PM TSTM WND GST 4 WSW SAND SPRINGS 47.08N 107.57W
08/25/2020 M53 MPH GARFIELD MT MESONET
MESONET STATION 302000 4 WSW SAND SPRINGS.
&&
BCBSpecial Weather Statement
National Weather Service Glasgow MT
923 PM MDT Tue Aug 25 2020
MTZ017-022-023-026-260415-
Garfield MT-Prairie MT-McCone MT-Central and Southern Valley MT-
923 PM MDT Tue Aug 25 2020
...SIGNIFICANT WEATHER ADVISORY FOR GARFIELD...SOUTH CENTRAL
VALLEY...SOUTHWESTERN MCCONE AND NORTHWESTERN PRAIRIE COUNTIES UNTIL
1015 PM MDT...
At 922 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 13 miles northwest of Hell Creek Rec Area to 15
miles south of Sand Springs. Movement was east at 20 mph.
Wind gusts up to 50 mph will be possible with these storms.
Locations impacted include...
Jordan, Hell Creek Rec Area, Flowing Wells Rest Area, Cohagen, Nelson
Creek Rec Area, Rock Creek Rec Area, Hillside, Crow Rock and Van
Norman.
LAT...LON 4686 10672 4687 10736 4781 10719 4771 10592
4686 10599 4686 10609 4685 10609 4684 10672
TIME...MOT...LOC 0322Z 258DEG 8KT 4775 10711 4688 10737
NWS GlasgowThe Glasgow radar (KGGW), 100 km away, was scanning. The volume nearest the first event began at 03:33 UTC.
1 thunderstorm wind. Local standard time, as filed.
At the Jordan airport ASOS site (KJDN), a 69 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: 912879.