Showers and thunderstorms developed via daytime heating of higher terrain in Southwest MT before moving northeastward. Sufficiently-strong vertical wind shear contributed to several instances of severe wind gusts as these storms affected North-Central MT.
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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 TFX wrote it up.
Showers and thunderstorms developed via daytime heating of higher terrain in Southwest MT before moving northeastward. Sufficiently-strong vertical wind shear contributed to several instances of severe wind gusts as these storms affected North-Central MT.
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 Great Falls, MT wrote its last area forecast discussion before the first event at Aug 11, 1:50 PM MST, 2 hours 25 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 250 PM MDT Sat Aug 11 2018 .SYNOPSIS... A few showers and thunderstorms are expected across mainly southwest and central Montana this afternoon and evening. Any shower or storm will be capable of producing gusty and erratic winds. Little precipitation is expected with the showers and storms through tonight. A Pacific front will then sweep east across the region tonight, bringing breezy winds and slightly cooler temperatures for the day on Sunday. && .DISCUSSION... Rest of this Afternoon through Sunday...Upper level low over the Salish Sea this afternoon will lift NE into British Columbia tonight and then dampen to a wave traversing the Canadian Prairies Sunday and Monday. This feature will effectively break down the strong upper ridge that has brought record heat to the region this past week. A narrow plume of mid level moisture is being drawn north ahead of the trough and will be in place across the Northern Rockies this afternoon/evening, which combined with the terrain heating/increasing synoptic lift will lead to isolated to scattered thunderstorm development over ID/SW MT this afternoon, tracking NE into central MT this evening. Moisture is very limited across the Northern Rockies, which has led to classic deep inverted-V soundings. Any shower or thunderstorm will be capable of producing gusty winds and little precipitation this afternoon/evening, however, enough shear is present thanks to increasing winds aloft ahead of the trough for a small chance of an isolated stronger thunderstorm. Pacific front sweeps east across the region overnight, brining the first round of cooling with another front of Canadian origins moving south through the area Sunday and Sunday night, bringing more significant cooling. - Hoenisch/Moldan Monday through Saturday...Coolest temperatures of the period are on track for Monday as the Canadian airmass slides east into the Dakotas with Monday afternoon temperatures as much as 10 degrees below seasonal averages across north-central MT. A zonal westerly flow is in place across the region through much of the upcoming week with upper level ridging likely to redevelop along the west coast by next weekend. Temperatures quickly warm back above seasonal averages by mid week then warm further late next week again. Embedded weather disturbances along with occasional pulses of monsoon related moisture may bring a small chance of thunderstorms to portions of SW MT next week. Hoenisch && .AVIATION... Updated 1755Z. VFR conditions will prevail through the period with some minor exceptions. Isolated to scattered thunderstorms will develop mainly over SW and Central MT this afternoon and evening. These will track northeast across the area with local MVFR conditions in the vicinity of stronger storms. Surface winds will increase this afternoon with a shift to NW winds likely over north-central MT and a more general shift to westerly expected in all areas tonight as a Pacific cold front moves across the region. Gusty and erratic winds are also likely near any thunderstorm activity this afternoon and evening. Britton && .FIRE WEATHER... Red Flag Waring continues for all districts this afternoon/evening for multiple fire weather hazards. Isolated to scattered thunderstorms producing little precipitation are expected this afternoon and evening across most of the region. In addition to the potential for new lightning fire ignitions, gusty and erratic winds are likely near any thunderstorm activity. - Hoenisch/Moldan Humidity improves tonight with the passage of the Pacific cold front but will lower again into the teens Sunday afternoon along with widespread breezy west winds. This will likely require additional fire weather highlights for Sunday, though confidence is not as high due to potential cloud-cover over southern districts and marginal humidity across northern areas where winds will be strongest. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 59 92 46 76 / 50 0 0 0 CTB 56 81 48 70 / 40 0 0 10 HLN 59 88 54 80 / 60 0 0 0 BZN 53 92 49 84 / 30 10 10 0 WEY 41 82 39 80 / 0 10 10 10 DLN 54 89 47 82 / 30 10 0 0 HVR 61 92 50 75 / 60 0 0 0 LWT 61 89 52 73 / 40 10 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 9 PM MDT Sunday Central and Eastern Lewis and Clark National Forest Areas...Chouteau and Fergus Counties... Deerlodge/Western Beaverhead National Forest...Eastern Beaverhead National Forest...Eastern Glacier/Toole/Central/Eastern Pondera/Liberty...Helena and Townsend Ranger Districts of the Helena National Forest...Hill and Blaine Counties...Lewis and Clark National Forest Rocky Mountain District-Rocky Mountain Front...Lincoln Ranger District of the Helena National Forest. Heat Advisory until 9 PM MDT this evening Blaine...Cascade... Chouteau...Eastern Pondera...Eastern Teton...Fergus...Hill... Judith Basin...Liberty...Toole. Red Flag Warning until midnight MDT Sunday night Gallatin National Forest. && http://www.weather.gov/greatfalls
Special Weather Statement
National Weather Service Great Falls MT
507 PM MDT SAT AUG 11 2018
MTZ014-048-112330-
Southern Rocky Mountain Front MT-
Central and Southern Lewis and Clark MT-
507 PM MDT SAT AUG 11 2018
...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL LEWIS AND CLARK COUNTY
UNTIL 530 PM MDT...
At 506 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles southeast of Lincoln, or 30 miles northwest of Helena, moving
northeast at 40 to 50 mph.
Winds in excess of 40 mph will be possible with this storm.
Locations impacted include...
Lincoln, Wolf Creek, Canyon Creek and Craig.
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 4733 11234 4710 11193 4667 11241 4670 11242
4670 11253 4684 11254 4683 11276 4686 11280
TIME...MOT...LOC 2306Z 212DEG 44KT 4687 11253
JANGLINThe Missoula radar (KMSX), 229 km away, was scanning. The volume nearest the first event began at 23:13 UTC.
5 thunderstorm wind. Local standard time, as filed.
Large healthy conifer tree downed at the roots in high winds from thunderstorm. Estimated peak gust of 60 mph.
Sensor measured 58 mph wind gust.
Sensor measured 58 mph wind gust.
Strong winds knocked down some tree branches up to 33 inches in length. Estimated wind gust 58 mph.
DOT Sensor measured 67 mph gust.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2018Every state in 2018This day in weather historyWarnings in Montana, August 2018
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: 768078, 768085, 768083, 768081, 768082.