Scattered showers and thunderstorms developed via daytime heating of higher terrain and along a Pacific cold front as it advanced eastward during the afternoon and evening hours of the 21st. An isolated severe thunderstorm managed to occur near Cameron in Madison 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 TFX wrote it up.
Scattered showers and thunderstorms developed via daytime heating of higher terrain and along a Pacific cold front as it advanced eastward during the afternoon and evening hours of the 21st. An isolated severe thunderstorm managed to occur near Cameron in Madison 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 Great Falls, MT wrote its last area forecast discussion before the first event at Jul 21, 4:50 PM MST, 44 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 550 PM MDT Sat Jul 21 2018 ...UPDATED AVIATION SECTION... .SYNOPSIS... Isolated showers and thunderstorms are possible Saturday evening across central and southwest Montana. A cold front will move through the region overnight, producing cooler temperatures on Sunday. Fair and seasonally warm temperatures prevail into next week. && .DISCUSSION... Warm and dry conditions prevail across the region this afternoon. Observed relative humidity has dropped below 20 percent at many locations. Winds remain generally light, but are increasing along the Rocky Mountain Front. Winds are expected to increase through the evening ahead of an advancing cold front, thereby creating critical fire weather conditions for a least a short time late this afternoon. Short- term model guidance indicates an increasing potential for isolated showers and thunderstorms along and ahead of the cold front. Appreciable instability and moderate to strong vertical wind shear may allow a few thunderstorms to produce small hail and strong wind gusts, especially later this afternoon and evening. Satellite imagery shows continued cumulus development across southwest Montana, providing observed support for these model trends. It will be mostly dry on Sunday, with cooler afternoon temperatures as high pressure builds in behind the front. Fair and seasonally warm temperatures prevail into next week. Longer range models are in slightly better agreement for the extended period, Tuesday through Saturday. A more northwesterly flow aloft is expected over the region from Wednesday through Friday, as upper level disturbances move southward through the region. Scattered showers/thunderstorms are expected as the disturbance moves through. Overall, uncertainty remains in terms of timing/amount of precipitation late next week. Models are showing warmer/drier conditions making a return to the region for next weekend. && .AVIATION... Updated 2350Z. VFR conditions are generally expected across north central and southwest Montana at least through the day on Sunday. The passage of a shortwave trough and associated cold front will mostly cause a shift in the wind from southerly to west-northwest from west to east through 07Z. Winds will mostly be 10 to 20 kt with gusts to 35 kt. However, scattered thunderstorms have formed along the front in southwest Montana as of 2350Z and these storms will move northeast through central Montana (KLWT) through 06Z. Some storms may produce brief MVFR conditions and gusts to 40 kt. Skies will otherwise be clear with less gusty winds after 06Z, but northwest wind gust to 20 kt will likely linger through the remainder of the period over the eastern TFX plains (KHVR KLWT). Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 50 79 52 84 / 10 0 0 0 CTB 47 76 47 77 / 0 0 0 0 HLN 54 82 52 86 / 0 0 0 0 BZN 50 81 49 85 / 10 0 0 0 WEY 43 77 41 79 / 10 0 0 0 DLN 48 81 47 84 / 0 0 0 0 HVR 54 79 51 85 / 10 0 0 0 LWT 52 74 49 81 / 20 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until midnight MDT tonight Central and Eastern Lewis and Clark National Forest Areas...Chouteau and Fergus Counties...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. && http://www.weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
556 PM MDT SAT JUL 21 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0425 PM TSTM WND GST 4 SSE DILLON 45.17N 112.61W
07/21/2018 M51 MPH BEAVERHEAD MT TRAINED SPOTTER
&&
SACSpecial Weather Statement
National Weather Service Great Falls MT
603 PM MDT SAT JUL 21 2018
MTZ008-015-055-220030-
Madison-Beaverhead-Gallatin-
603 PM MDT SAT JUL 21 2018
...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN MADISON...
SOUTHEASTERN BEAVERHEAD AND EAST CENTRAL GALLATIN COUNTIES...
At 601 PM MDT, radar indicated strong thunderstorms were located
along a line extending from near Bozeman Pass southwest to near
Monida. Movement was east at 30 mph.
Wind gusts up to 50 mph, hail up to pea size, and brief heavy rain
are possible with these storms.
Locations impacted include...
Bozeman, Gallatin Gateway and Big Sky.
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.
These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
LAT...LON 4462 11224 4597 11080 4560 11080 4559 11086
4553 11086 4552 11092 4540 11092 4535 11097
4535 11104 4528 11104 4464 11172
TIME...MOT...LOC 0001Z 258DEG 26KT 4629 11038 4469 11210
CoulstonSpecial Weather Statement National Weather Service Great Falls MT 606 PM MDT SAT JUL 21 2018 MTZ053>055-220030- Broadwater-Gallatin-Meagher- 606 PM MDT SAT JUL 21 2018 ...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT CENTRAL BROADWATER... CENTRAL MEAGHER AND NORTHERN GALLATIN COUNTIES... At 605 PM MDT, strong thunderstorms were clustered near Townsend, moving northeast at 45 mph. Winds in excess of 40 mph and brief heavy rain are possible with this storm. Locations impacted include... Townsend, White Sulphur Springs, Toston, Fort Logan On The Smith River, Newlan Creek Reservoir, Silos and Fort Logan. If you are on or near Canyon Ferry Lake, get out of the water and move indoors or inside a vehicle. Remember, lightning can strike out to 10 miles from the parent thunderstorm. If you can hear thunder, you are close enough to be struck by lightning. Move to safe shelter now! Do not be caught on the water in a thunderstorm. LAT...LON 4610 11147 4635 11176 4687 11111 4654 11067 TIME...MOT...LOC 0005Z 223DEG 52KT 4634 11143 Coulston
Special Weather Statement National Weather Service Great Falls MT 629 PM MDT SAT JUL 21 2018 MTZ053-054-220100- Broadwater-Meagher- 629 PM MDT SAT JUL 21 2018 ...A STRONG THUNDERSTORM WILL AFFECT EAST CENTRAL BROADWATER AND SOUTHEASTERN MEAGHER COUNTIES... At 628 PM MDT, a strong thunderstorm was located 17 miles southwest of White Sulphur Springs, moving northeast at 45 mph. Winds in excess of 40 mph, brief heavy rain, and hail up to pea size are possible with this storm. Locations impacted include... White Sulphur Springs and Newlan Creek Reservoir. 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. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. LAT...LON 4622 11117 4638 11135 4673 11082 4646 11053 TIME...MOT...LOC 0028Z 232DEG 38KT 4636 11115 Coulston
Special Weather Statement
National Weather Service Great Falls MT
632 PM MDT SAT JUL 21 2018
MTZ008-015-055-220100-
Madison-Beaverhead-Gallatin-
632 PM MDT SAT JUL 21 2018
...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN MADISON...
SOUTHEASTERN BEAVERHEAD AND CENTRAL GALLATIN COUNTIES...
At 631 PM MDT, radar indicated strong thunderstorms were located
along a line extending from 11 miles southeast of Bozeman to 15 miles
north of Kilgore. Movement was east at 30 mph.
Winds in excess of 40 mph and brief heavy rain are possible with
these storms.
Locations impacted include...
Big Sky, Red Rock Pass, Raynolds Pass and Lakeview.
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 4460 11192 4506 11165 4559 11106 4565 11080
4553 11086 4552 11092 4536 11092 4535 11104
4508 11104 4511 11110 4505 11115 4501 11110
4490 11110 4470 11130 4475 11139 4471 11141
4470 11149 4457 11151
TIME...MOT...LOC 0031Z 258DEG 26KT 4559 11083 4462 11181
CoulstonThe Pocatello radar (KSFX), 243 km away, was scanning. The volume nearest the first event began at 00:32 UTC.
1 thunderstorm wind. Local standard time, as filed.
Mesonet recorded 61-mph thunderstorm wind gust 2-miles SSW of Cameron.
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, July 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: 759977.