A line of severe thunderstorms brought high winds and tree damage during the morning hours.
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 MSO wrote it up.
A line of severe thunderstorms brought high winds and tree damage during the morning hours.
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 Missoula, MT wrote its last area forecast discussion before the first event at May 31, 3:04 AM MST, 3 hours 41 minutes earlier.
Area Forecast Discussion National Weather Service Missoula MT 404 AM MDT Sun May 31 2020 .DISCUSSION...A slow moving low pressure system is slowly making is way into the Northern Rockies this morning. Numerous showers and thunderstorms, some strong, extend off this low from Eastern Washington and Oregon into Southern Idaho. Showers are rapidly developing across central Idaho into western and southwest Montana. These are expected to strengthen into the early morning hours. Movement of all showers and storms will generally be from south to north with the brunt of the stronger storms impacting central Idaho into portions of Northwest Montana. This system will quickly move northward this afternoon. Scattered showers and a few thunderstorms are expected to linger across Northwest Montana along the Canadian Border this afternoon. The overall weather pattern will transition to a westerly flow aloft. A few weak disturbances will trigger rain showers through Wednesday. A trough of low pressure will amplify across the Pacific Northwest Thursday and Friday. This will leave the Northern Rockies in a moist southwesterly flow. The increased moisture and instability is expected to trigger showers and thunderstorms across Lemhi county Idaho into Southwest Montana Thursday. Right now it looks like shower and thunderstorm activity will extend further north Friday impacting much of western Montana and central Idaho. Models do show the upper low moving into the Northern Rockies Saturday and Sunday and bringing widespread possibly significant precipitation. However there are considerable model differences with timing and location of most precipitation. The main message for next weekend is wetter and cooler with exact details to come later this week. && .AVIATION...A low pressure system will continue to push band of showers and thunderstorms through the Northern Rockies today. Currently a band of showers extend across north central Idaho into west central Montana and will steadily move northward into northwest Montana. KGPI, KMSO and KBTM will experience vicinity showers through 31/12z. A more robust line of showers and thunderstorms will be moving into the Northern Rockies later this morning. This line of storms will be capable of producing dangerous erratic winds, small hail and heavy rain. The path of the storms appears to mainly impact north central Idaho up into northwest Montana. A storm could graze KMSO around 31/14z. While KGPI should be heavily impacted by thunderstorms between 31/14z to 31/18z. As this band moves through the area, gusty westerly winds will mix to the surface causing breezy conditions for the remainder of the day. Wind gusts up to 30 mph will be possible in valley locations and the higher terrain of northwest Montana could experience gusts in excess of 40 mph. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
Special Weather Statement
National Weather Service Missoula MT
322 AM PDT Sun May 31 2020
IDZ006>008-311115-
Southern Clearwater Mountains ID-
Lower Hells Canyon/Salmon River Region ID-
Orofino/Grangeville Region ID-
322 AM PDT Sun May 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL IDAHO COUNTY UNTIL
415 AM PDT...
At 322 AM PDT, Doppler radar was tracking a strong thunderstorm 12
miles north of Riggins, or 27 miles southwest of Grangeville, moving
north at 35 mph.
Half inch hail and winds in excess of 40 mph will be possible with
this storm.
Locations impacted include...
White Bird, Slate Creek, Copperville, Canfield and Lucile.
LAT...LON 4594 11641 4579 11597 4545 11636 4555 11651
4558 11648 4562 11646 4569 11654 4572 11654
TIME...MOT...LOC 1022Z 201DEG 29KT 4559 11641Special Weather Statement
National Weather Service Missoula MT
425 AM PDT Sun May 31 2020
IDZ005-007-311215-
Northern Clearwater Mountains ID-Orofino/Grangeville Region ID-
425 AM PDT Sun May 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL IDAHO AND WESTERN
CLEARWATER COUNTIES UNTIL 515 AM PDT...
At 424 AM PDT, Doppler radar was tracking a strong thunderstorm near
Orofino, moving north at 55 mph.
Half inch hail and winds in excess of 50 mph will be possible with
this storm.
Locations impacted include...
Orofino, Elk River, Ahsahka, Dent, Greer, Teakean, Woodland and
Riverside.
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.
&&
LAT...LON 4664 11633 4693 11633 4693 11570 4627 11603
4628 11611 4641 11620 4641 11630 4647 11637
4650 11637 4650 11644 4663 11645
TIME...MOT...LOC 1124Z 193DEG 47KT 4639 11620Special Weather Statement
National Weather Service Missoula MT
633 AM MDT Sun May 31 2020
IDZ005-006-MTZ001-003>006-043-311330-
Southern Clearwater Mountains ID-Northern Clearwater Mountains ID-
Flathead/Mission Valleys MT-Bitterroot/Sapphire Mountains MT-
Missoula/Bitterroot Valleys MT-Lower Clark Fork Region MT-
Kootenai/Cabinet Region MT-Potomac/Seeley Lake Region MT-
633 AM MDT Sun May 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN IDAHO...NORTHEASTERN
CLEARWATER...MINERAL...SOUTH CENTRAL LAKE...SOUTHWESTERN MISSOULA...
SOUTHERN SANDERS AND NORTHWESTERN RAVALLI COUNTIES UNTIL 730 AM
MDT/630 AM PDT/...
At 630 AM MDT/530 AM PDT/, Doppler radar was tracking strong
thunderstorms along a line extending near Avery, Idaho through
Powell, Idaho to Hamilton, Montana. Movement was northeast at 40
mph.
Pea size hail and winds in excess of 40 mph will be possible with
these storms.
Locations impacted include...
Missoula, Hamilton, Thompson Falls, Superior, Lolo, Stevensville,
Plains, Alberton, Florence, Tarkio, Victor, Riverbend, Arlee,
Woodside, Wye, De Borgia, Evaro, St. Regis, Bonner-West Riverside and
Haugan.
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.
&&
LAT...LON 4747 11563 4751 11570 4768 11532 4737 11463
4706 11375 4602 11406 4693 11544 4694 11496
4697 11501 4697 11505 4710 11514 4719 11530
4726 11533 4730 11553 4737 11558 4743 11576
TIME...MOT...LOC 1230Z 221DEG 133KT 4783 11505 4690 11358Special Weather Statement
National Weather Service Missoula MT
656 AM MDT Sun May 31 2020
IDZ010-MTZ005-006-311330-
Eastern Lemhi County ID-Bitterroot/Sapphire Mountains MT-
Missoula/Bitterroot Valleys MT-
656 AM MDT Sun May 31 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN LEMHI...CENTRAL RAVALLI
AND SOUTHWESTERN GRANITE COUNTIES UNTIL 730 AM MDT...
At 655 AM MDT, Doppler radar was tracking a strong thunderstorm 11
miles southeast of Conner, or 32 miles south of Hamilton, moving
northeast at 50 mph.
Half inch hail and wind gusts up to 50 mph will be possible with this
storm.
Locations impacted include...
Sula.
LAT...LON 4577 11385 4578 11387 4568 11401 4575 11418
4623 11386 4609 11352
TIME...MOT...LOC 1255Z 210DEG 42KT 4579 11402Special Weather Statement National Weather Service Missoula MT 712 AM MDT Sun May 31 2020 MTZ001>004-043-311345- Flathead/Mission Valleys MT-West Glacier Region MT- Lower Clark Fork Region MT-Kootenai/Cabinet Region MT- Potomac/Seeley Lake Region MT- 712 AM MDT Sun May 31 2020 ...SIGNIFICANT WEATHER ADVISORY FOR LAKE...NORTHEASTERN MISSOULA... SOUTH CENTRAL LINCOLN...EASTERN SANDERS...SOUTHWESTERN FLATHEAD AND NORTHWESTERN POWELL COUNTIES UNTIL 745 AM MDT... At 710 AM MDT, Doppler radar was tracking strong thunderstorms along a line extending from near Thompson Falls to 9 miles east of Evaro. Movement was northeast at 55 mph. Pea size hail and winds in excess of 40 mph will be possible with these storms. Locations impacted include... Polson, Ravalli, Ronan, Plains, St. Ignatius, Turtle Lake, Arlee, Rocky Point, Old Agency, Kerr, Pablo, Jette, Kings Point, Dixon, Big Arm, Evaro, Hot Springs, Moiese, Kicking Horse and Condon. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heavy rainfall is also occurring with these storms, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 4824 11514 4747 11337 4698 11382 4767 11541 TIME...MOT...LOC 1310Z 204DEG 46KT 4768 11530 4706 11389
The Missoula radar (KMSX), 78 km away, was scanning. The volume nearest the first event began at 13:43 UTC.
2 thunderstorm wind. Local standard time, as filed.
Numerous tree damage led to power outages and blocked roadways. Damage was noted on both sides of Flathead Lake, but damage was most concentrated near Polson, Dayton, and Finley Point.
Widespread high winds were reported as a line of thunderstorms, in the form of a squall line, moved north-northeastward across the region. While wind gusts of 50 to 60 miles per hour were common, a person from the public in Kila reported a measured peak wind gust of 78 miles per hour, and the ASOS at Glacier Park International Airport recorded a peak wind gust of 69 miles per hour. Numerous trees were either snapped in half or uprooted, which resulted in over 200 power outages and 37,000 customers without power. Several houses and vehicles were destroyed as trees fell onto them. Highway 2 and Montana Highway 83 were both covered by fallen trees for a time. A local electric coop remarked that this wind event may be the largest, most damaging outage event in our history.
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, May 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: 884103, 884102.