One isolated severe thunderstorm tracked NE from Lost Trail to Georgetown Lake to Garrison to Elliston and eventually Great Falls. Strong shear and modest instability allowed for the storm to maintain its structure and become a long-tracked super cell.
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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 MSO wrote it up.
One isolated severe thunderstorm tracked NE from Lost Trail to Georgetown Lake to Garrison to Elliston and eventually Great Falls. Strong shear and modest instability allowed for the storm to maintain its structure and become a long-tracked super cell. Both wind and hail damage were reported throughout the track, with one fatality blamed on the storm as a wind gust blew over a tree onto a woman near Elliston.
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 6, 3:00 AM MST, 9 hours 40 minutes earlier.
Area Forecast Discussion National Weather Service Missoula MT 400 AM MDT Sat May 6 2017 .DISCUSSION...Scattered rain showers will continue this morning across western Montana and central Idaho. A brief break will be possible around mid day today before the next round of showers and thunderstorms moves in this afternoon. The focus for thunderstorms this afternoon will be over southwest Montana, Lemhi county of Idaho and parts of west-central Montana. The main threats will be small hail and gusty winds with wind gusts of 50 mph possible. An isolated severe storm will be possible with the best chances over Lemhi county and southwest Montana near the Continental Divide. A cold front will move through the region this afternoon/evening and temperatures in most locations will run 5 to 10 degrees below seasonal averages on Sunday. Showery conditions will persist on Sunday especially over the higher terrain near the Continental Divide. For the first half of next week, the forecast dries out and temperatures will be on the increase again, reaching widespread 70s by Wednesday. The warm temperatures will again increase the rate of snowmelt in the terrain, so expect streams to be running high and swiftly through the week. Showers and thunderstorms are back in the forecast by Thursday and Friday of next week, as a trough of low pressure pushes into the West Coast. && .AVIATION...Showers will decrease this morning giving area terminals a break after 12Z. This afternoon a cold front will move through the region causing another round of thunderstorms and showers. Storm motion is expected to be 30-40 knots, so any impacts from storms at area terminals will be short lived. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
Special Weather Statement National Weather Service Missoula MT 1211 PM MDT SAT MAY 6 2017 IDZ009-010-MTZ006-061900- Eastern Lemhi County ID-Western Lemhi County ID- Bitterroot/Sapphire Mountains MT- 1211 PM MDT SAT MAY 6 2017 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN LEMHI AND SOUTHWESTERN RAVALLI COUNTIES UNTIL 100 PM MDT... At 1210 PM MDT, Doppler radar was tracking a strong thunderstorm 28 miles southwest of North Fork, or 29 miles west of Salmon, moving northeast at 35 mph. Pea size hail, heavy rain, and winds in excess of 40 mph will be possible with this storm. Locations impacted include... Shoup. PRECAUTIONARY/PREPAREDNESS ACTIONS... Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 4509 11438 4517 11464 4572 11440 4557 11393 TIME...MOT...LOC 1810Z 203DEG 32KT 4521 11451
Special Weather Statement
National Weather Service Missoula MT
1255 PM MDT SAT MAY 6 2017
IDZ009-010-MTZ005-006-061945-
Eastern Lemhi County ID-Western Lemhi County ID-
Bitterroot/Sapphire Mountains MT-Missoula/Bitterroot Valleys MT-
1255 PM MDT SAT MAY 6 2017
...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL LEMHI AND
SOUTHEASTERN RAVALLI COUNTIES UNTIL 145 PM MDT...
At 1254 PM MDT, Doppler radar was tracking a strong thunderstorm 14
miles northwest of North Fork, or 29 miles northwest of Salmon,
moving northeast at 35 mph.
Dime size hail, brief heavy rain, and winds in excess of 40 mph will
be possible with this storm.
Locations impacted include...
Conner, Sula and Lost Trail Pass.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 4584 11370 4575 11383 4578 11387 4576 11390
4570 11391 4570 11393 4568 11394 4564 11390
4562 11390 4562 11388 4540 11418 4549 11440
4603 11410 4584 11362
TIME...MOT...LOC 1854Z 210DEG 32KT 4552 11424The Missoula radar (KMSX), 129 km away, was scanning. The volume nearest the first event began at 19:42 UTC.
5 hail, 2 thunderstorm wind. Local standard time, as filed.
Resident reported mostly nickel-sized hailstones, with a few quarter-sized hailstones mixed in. No evidence of damage to property was seen. Resident estimated wind speeds with the storm outflow at 40 to 50 mph. Frequent lightning was also reported.
A RAWS station east of Sula recorded 66 mph winds.
A local resident reported ground covered with quarter-sized hail. A few strikes of lightning accompanied the storm.
A trained spotter in Georgetown Lake reported half-dollar size hail.
NWS employee reported quarter size hail 5 miles east of Garrison Junction. The hailstones were found one hour after the storm had passed. Thus, the hailstones were likely larger when it initially fell.
The media reported A Montana woman was killed when a tree struck her during a weekend thunderstorm. She was reportedly running back to camp when a tree broke, striking her on the head. She died on the way to the hospital.
Large hail of 1 in diameter was reported by citizen at the Garrison Mercantile in Garrison at 3:57 pm MDT.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Thunderstorm Wind, Powell | 2017-05-06 | 41 | Female | Outside/Open Areas | Indirect |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2017Every state in 2017This day in weather historyWarnings in Montana, May 2017
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: 699713, 687395, 687398, 693627, 693629, 693652, 693630.