A near stationary low pressure surface trough, warm moist air from the southeast and a strong cold front from the west all combined to allowed many severe thunderstorms to develop and strengthen through the afternoon and evening hours. Later that evening and night, larger-scale post-frontal non-thunderstorm high winds brought additional damage.
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 near stationary low pressure surface trough, warm moist air from the southeast and a strong cold front from the west all combined to allowed many severe thunderstorms to develop and strengthen through the afternoon and evening hours. Later that evening and night, larger-scale post-frontal non-thunderstorm high winds brought additional damage.
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 Jun 10, 3:32 AM MST, 10 hours 26 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 432 AM MDT Thu Jun 10 2021 .DISCUSSION... The stage is set today for another evening of severe thunderstorms. The recently persistent large-scale SW flow aloft will push an embedded smaller-scale disturbance or wave impulse through the flow this afternoon and evening from Idaho into southern Montana. At the surface, in response to this forcing, a strong inverted surface low pressure trough will set an characterize a dry slot in the overall weather system. Enough moist air will be advected just on the east and northeast side of this dry slot to destabilize the local atmosphere, that thunderstorms will easily form and strengthen. All the necessary ingredients for very large hail, severe wind gusts in excess of 70 mph, and even a few tornadoes. SPC maintains an enhanced outlook area for most of our CWA, with hatched areas for hail and winds and a 5 percent chance of tornadoes. Some of these chances may be increased with SPC updates today. Most model consensus shows storm development in two separate locations around 2 or 3 o'clock this afternoon: 1) along the S-N surface pressure trough and dry slot, and 2) further west, downslope of the higher elevation areas of central Montana. Most of the rest of the CWA will fill in with additional thunderstorms this evening before diminishing away toward the northeast during the overnight hours. Friday, a cooler, post-frontal, drier environment will be in place with persistent gusty west winds, keeping the need for the current Lake Wind Advisory in place. By Friday night, the main active and forcing mechanisms will be past and calmer conditions will return, allbeit under a building broad ridge of high pressure from the south. This will allow for a period of hot and dry weather to prevail this weekend and into next week. && .AVIATION... FLIGHT CONDITIONS: Mainly VFR early, then IFR to LIFR briefly as multiple thunderstorms sweep through the region during the afternoon and evening hours. All summertime severe weather threats will be possible. Expect amendments. LLWS: Possible due to severe thunderstorms. WINDS: Early, from the east and northeast at 20 kts; KSDY will remain gusty from the SE up to 30 kts through mid-day while other TAF sites will see temporary light and variable winds ahead developing storms. After 00Z this evening, a cold front will bring NW winds of 25 kts. SYNOPSIS: The weather pattern and ingredients are lining up for another round of severe thunderstorms this afternoon and evening. All summertime severe weather threats are possible. && .FIRE WEATHER... For locations which have recently received less precipitation than others, fire weather concerns will be raised again today, due to lower relative humidity and strong, gusty winds. The areas of concern are a little tricky, with timing, but our best information places the lowest RH values along the dry slot and surface pressure trough. These conditions last the longest, east of Garfield County and south of MT-Highway 200 (generally the southern portion of Fire Weather Zone 137). A Red Flag Warning has been issued for this area. Further west, we are expecting a more sudden recovery in RH vales as the front approaches, ending only a few hours of concern there. && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Lake Wind Advisory until 7 PM MDT Friday For Fort Peck Lake for Central and Southeast Phillips...Central and Southern Valley... Garfield...McCone...Petroleum. Red Flag Warning from 11 AM this morning to 8 PM MDT this evening for MTZ122. && weather.gov/glasgow
PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE GLASGOW MT
904 AM MDT THU JUN 10 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0715 PM HAIL 7 W LANDUSKY 47.89N 108.77W
06/09/2021 E1.00 INCH PHILLIPS MT TRAINED SPOTTER
ALSO WIND GUST TO 62 MPH WITH BRIEF HEAVY
RAIN.
0719 PM TSTM WND GST 5 SSW HAYS 47.92N 108.73W
06/09/2021 M57 MPH PHILLIPS MT DEPT OF HIGHWAYS
.
0719 PM TSTM WND GST 5 WNW LANDUSKY 47.92N 108.73W
06/09/2021 M56 MPH PHILLIPS MT MESONET
WIND GUST FROM MESONET STATION MTHAY 6.1 SW
HAYS (MT DOT). SUSTAINED WIND 44 MPH.
0730 PM HAIL 8 SW PHILLIPS 48.02N 108.29W
06/09/2021 M2.00 INCH PHILLIPS MT PUBLIC
TWITTER PHOTO OF HAILSTONES WITH
MEASUREMENT. TIME ESTIMATED.
0740 PM HAIL ZORTMAN 47.92N 108.53W
06/09/2021 E3.00 INCH PHILLIPS MT PUBLIC
PUBLIC REPORT OF HAIL 2 TO 3 INCHES,
POSSIBLY LARGER. SOME PEOPLE AT NEARBY
CAMPGROUND ALSO SUSTAINED DAMAGE. BUSTED
WINDSHIELDS AND DENTED VEHICLES. NOT VERY
WINDY, A LOT OF RAIN. TIME ESTIMATED.
0740 PM HAIL ZORTMAN 47.92N 108.53W
06/09/2021 M1.70 INCH PHILLIPS MT PUBLIC
PHOTO SUBMITTED SHOWING GOLF BALL SIZED HAIL
AND SHINGLE DAMAGE. TIME ESTIMATED.
0740 PM HAIL ZORTMAN 47.92N 108.52W
06/09/2021 M1.75 INCH PHILLIPS MT CO-OP OBSERVER
0800 PM HAIL 8 E ZORTMAN 47.93N 108.35W
06/09/2021 M3.00 INCH PHILLIPS MT PUBLIC
TWITTER PHOTO OF HAIL MEASUREMENT. TIME
ESTIMATED.
0802 PM HAIL 8 E ZORTMAN 47.92N 108.35W
06/09/2021 M2.50 INCH PHILLIPS MT STORM CHASER
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
1234 PM MDT THU JUN 10 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1038 PM HAIL 6 NNW FOURCHETTE 47.81N 108.04W
06/09/2021 M1.25 INCH PHILLIPS MT PUBLIC
PHOTO SUBMITTED THROUGH FACEBOOK. LOCATED
NEAR THE DRY FORK RD AND MIDALE RD.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
115 PM MDT THU JUN 10 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1000 PM TSTM WND GST 8 SW ZORTMAN 47.84N 108.65W
06/09/2021 E65 MPH PHILLIPS MT TRAINED SPOTTER
&&
BBThe Glasgow radar (KGGW), 122 km away, was scanning. The volume nearest the first event began at 20:56 UTC.
35 thunderstorm wind, 26 hail, 3 heavy rain. Local standard time, as filed.
Public reported a grain bin destroyed south of Flaxville on the R-Y Road. Time estimated from radar.
Trained spotter reported walnut size hail.
Trained spotter reported quarter size hail and heavy rain.
Public reported grain bins rolled, outbuildings damaged, and power poles knocked down.
Public reported hail up to the size of quarters.
Public reported, via Facebook, hail up to the size of quarters.
Public reported, via Facebook, golf ball size hail. Time and location are estimated.
Public reported, via Facebook, quarter size hail located off of US Highway 87, five miles north of the Musselshell County line. Time estimated from radar.
Public reported quarter size hail, which lasted for 20 minutes, along with heavy rain.
Richland County DES Coordinator reported hail up to the size of ping pong balls.
Public reported, via facebook, hen egg size hail located along the lost highway near Sidney.
Trained spotter reported a 60 mph thunderstorm wind gust.
Trained spotter reported ping pong ball size hail.
Public reported thunderstorm wind damage, via Facebook: A pivot was blown over; a grain bin was blown half a mile into a hay field; an outbuilding was destroyed; and the roof of another outbuilding was blown completely off.
Richland County DES Coordinator conducted a storm survey the morning after the storm and provided multiple reports and photos of straight-line wind damage in the town of Fairview with all debris lying in the same direction. Large spruce and cottonwood trees were uprooted; a metal building was caved in; and large tree branches were downed.
Public reported hail up to the size of golf balls.
Public measured golf ball size hail.
Trained spotter reported a tree, with a trunk at least 12 inches in diameter, blown down, as well as pea size hail in drifts.
Trained spotter reported tea cup size hail, along with torrential rainfall.
Trained spotter reported multiple trees damaged: Ash trees snapped; Apple trees blown down; and an 80-year old spruce tree blown down.
Trained spotter reported hen egg size hail.
Public reported, via Facebook, hail up to the size of baseballs. Time is estimated.
Public reported, via Facebook, hail up to the size of quarters. Time estimated from radar.
Public reported, via Facebook, four inches of storm total rainfall. Time estimated from rainfall.
Big Sheep Mountain RAWS site (LCFM8) recorded a 59 mph thunderstorm wind gust.
Public reported hurricane force wind gusts, power poles nearly blown over, and 75-year old trees blown over.
Public reported baseball size hail, possibly larger.
Trained spotter shared a photo report, via Twitter, of hen egg size hail covering the ground.
Trained spotter reported tea cup size hail.
Public reported, via Facebook, baseball size hail in the town of Lindsay.
Public reported, via Facebook, an estimated 90 mph thunderstorm wind gust. Time estimated from radar.
Public reported hail up to the size of quarters.
Trained spotter reported thunderstorm wind gust damage via Facebook: House soffit three feet in length was torn of a house; a dead tree was blown over; and live tree branches were downed.
Trained spotter reported, via Facebook, hail up to the size of golf balls. Time estimated by radar.
Several power line poles (both from the local electric cooperative and the Department of Energy, which were replaced in recent years) were snapped at their bases in this area. A nearby home weather station recorded a 79 mph thunderstorm wind gust.
Public reported more than four inches of rainfall.
Public reported thunderstorm wind gust damage via Facebook: Windows were broken; crops and gardens were damaged; and pine trees were toppled.
Public reported, via Facebook, hail up to the size of half dollars, along with strong winds.
Public reported hail up to the size of quarters covering the ground.
Public estimated a 70 mph thunderstorm wind gust which blew some tree branches down.
The Badger Creek mesonet site (FW2498) measured a 61 mph thunderstorm wind gust.
The mesonet site (FW8536), located northwest of Savage, measured a 66 mph thunderstorm wind gust.
The mesonet site (DW8636), 2 N Savage, measured a 66 mph thunderstorm wind gust.
Public estimated thunderstorm wind gusts around 75 mph.
Public reported windows blown out from thunderstorm wind gusts.
Public estimated quarter size hail.
Numerous power line poles were snapped at their bases, from County Road 201 southward on County Road 328 for a distance of up to 6 miles. Only a few poles were snapped about a third of the way up.
Several newer and well-built homes in the town of Lambert were damaged, including siding stripped from the southwest corners.
Several newer and well-built homes in the town of Lambert were damaged, including siding stripped from the southwest corners. Hail stones at least the size of quarters were assumed.
The mesonet site near Lambert (DW8633) measured a 70 mph thunderstorm wind gust.
The Brorson NDAWN mesonet site, 7 NW Sidney, measured a 74 mph thunderstorm wind gust.
The Brorson NDAWN mesonet site, 7 NW Sidney, measured a 90 mph thunderstorm wind gust.
Nearly a mile of power line poles were snapped either a third to half way up off the ground between county roads 130 and 129. A newer metal building in the area sustained roof damage on its southwest portion, which was blown away to the northeast. A mesonet station within three miles of this location measured a wind gust of 90 mph.
Storm chaser estimated hurricane force thunderstorm wind gusts.
Public reported, via Facebook, 2.5 inches of rain.
Public reported, via Facebook, a measured thunderstorm wind gust of 67 mph.
Public reported, via Facebook, multiple cases of thunderstorm wind damage: A stock trailer was rolled into a creek bottom; some shingles were blown off a roof; a barn wall was damaged; and a quonset door was lost.
Public reported, via Facebook, a single-wide trailer home was flipped over and destroyed. Time and location are estimated.
Storm chaser reported hurricane force thunderstorm wind gusts.
The US-2 @Stateline DOT site (MTSTA), recorded a 78 mph thunderstorm wind gust.
The US-2 @Stateline DOT site (MTSTA), recorded an 80 mph thunderstorm wind gust.
The Medicine Lake RAWS site (MLKM8) recorded a 65 mph thunderstorm wind gust.
Public estimated 80 mph thunderstorm wind gusts.
Public reported their outdoor propane tank was moved by severe thunderstorm wind gusts.
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, June 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: 968995, 968997, 968998, 968999, 969001, 969002, 969007, 969008, 969012, 969005, 969011, 969014, 969016, 969295, 969327, 969018, 969022, 969027, 969035, 969038, 969039, 969399, 969300, 969302, 969040, 969041, 969042, 969044, 969045, 969314, 969303, 969047, 969307, 969309, 969365, 969048, 969312, 969315, 969049, 969050, and more.