Scattered thunderstorms developed along and ahead of a Pacific cold front and shortwave trough during the afternoon and evening of June 21st. Moderate instability and vertical wind shear allowed multiple storms to become severe, resulting in numerous reports of severe wind gusts and several instances of severe hail.
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 TFX wrote it up.
Scattered thunderstorms developed along and ahead of a Pacific cold front and shortwave trough during the afternoon and evening of June 21st. Moderate instability and vertical wind shear allowed multiple storms to become severe, resulting in numerous reports of severe wind gusts and several instances of severe hail.
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 Jun 21, 11:05 AM MST, 2 hours 4 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1205 PM MDT Thu Jun 21 2018 .AVIATION UPDATE... Forecast remains on track. Thunderstorms are already starting to develop ahead of an upper level disturbance...giving us a sneak peak of what is to come today. So far looks like slow moving heavy rain type storms are likely. Expect thunderstorm to become more numerous this afternoon and continue through the evening. Best chances for the stronger storms still looks to be in the southwest and portions of the east where currently clear skies will bring ample instability. Some hail and strong winds are possible with these storms...although with high Pwats today the main threat will be heavy rain and possible flash flooding. Temperatures will continue to warm to near normal readings today...with some 80s possible. Anglin && .SYNOPSIS... Showers, thunderstorms, and localized flash flooding are possible today through Saturday as multiple weather disturbances move through the area. In addition, some thunderstorms may be severe this afternoon and early evening with quarter-size hail and damaging wind gusts. An overall drying trend is expected Saturday night into Sunday as high pressure builds over the area. Low temperatures will mainly be in the 50s, while highs will mainly reach the 70s or 80s through this weekend. && .DISCUSSION... Today through Saturday...An upper level disturbance will move from west to east across the region this afternoon/evening. Isolated thunderstorms this morning will become more widespread and stronger this afternoon. Some storms could strong/severe late this afternoon through early this evening. The airmass remains unsettled for Fri/Sat, with scattered showers and thunderstorms continuing. Some storms could produce heavy rain today through Saturday. There is a marginal risk of flash flooding today through Saturday, mainly south of a line from Helena to Lewistown. Afternoon temperatures will be seasonable through the period, generally within a few degrees of normal. Brusda Saturday night through Thursday...Shortwave trough exits our CWA to the east Saturday night, giving way to shortwave high pressure ridging for Sunday. Thus, an overall drying trend is expected as shower and thunderstorm probabilities decrease. On Monday, a longwave trough aloft and embedded disturbances are progged to slowly overspread our CWA from the west and break-down the shortwave ridge. In addition, a Pacific cold front looks to cross our CWA from west to east Monday night, perhaps resulting in some showers and thunderstorms. Appreciable instability and vertical wind shear may support a few severe thunderstorms and this potential scenario will continue to be monitored. The longwave trough aloft and embedded disturbances continue moving generally eastward over our region Tuesday through Wednesday. At this time, models suggest showers and thunderstorms will be isolated, but would not be surprised if the forecast trends wetter with future model runs. By next week Thursday, subtle high pressure ridging aloft is progged to build over our area behind the departing longwave trough, resulting in fair weather. Low temperatures trend near or slightly-above normal. Highs will be within several degrees of normal (i.e. mid 70's to lower 80's) for most days. The exception will be Monday, when strong warm advection ahead of the aforementioned longwave trough should contribute to highs reaching well into the 80's to lower 90's for most. - Jaszka .AVIATION... Updated 1805Z. Showers and thunderstorms will this afternoon and move northeastward. Some storms could be severe during the afternoon/evening hours. Storms will be decreasing by 06z Fri but a chance of rain showers will redevelop in many areas around 12Z Friday. && .HYDROLOGY... Lewis and Clark County...Flood warning will continue for the entire county. Flooding is slowly decreasing across the county but it will take time for all the flooding to end. Teton County...Flood Warning will continue for the whole county for potential further runoff. Flooding is decreasing in the western portion of the county with peak flows expected this morning in the eastern portions of the county on the Teton River. Cascade County...Flood Warning will continue. The Sun River has generally crested, and will slowly fall over the next few days. The Missouri River has crested at the city of Cascade, and should crest later today near moderate flood stage around Ulm. Jefferson River...between Whitehall and Trident...Flood warning continues. Minor flooding is expected into Friday. Meagher County...Flood warning continues for flooding around Martinsdale. This warning will be evaluated later this morning. Marias River south of Shelby...Flood Warning continues. Minor flooding is expected to continue through today. Pondera...Flood advisory continues into this evening. Broadwater County...Flood advisory continues into this morning for minor flooding around Toston. Big Hole River around Melrose...Flood Advisory continues for minor flooding through today. The river is showing a falling trend, so the minor flooding should not last too long in this region. Fergus County...A flood watch is currently out for the potential of heavy rain and new flooding or flash flooding on Thursday. Flooding may then continue into the weekend along the Missouri River...especially at the James Kipp Campground. Region wide...scattered showers and thunderstorms will affect the region for the next several days. There is the potential that some thunderstorms could produce brief periods of heavy rain and additional flooding or even flash flooding. A flood watch remains in effect for portions of North Central and Southwest MT. Any heavy rainfall over any areas currently under a flood warning or advisory could make the situation worse or extend the flooding problems. Anglin/Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 78 58 76 53 / 30 20 50 30 CTB 78 56 74 52 / 30 20 60 30 HLN 75 55 75 52 / 50 40 40 20 BZN 75 50 70 48 / 60 60 60 30 WEY 70 42 62 39 / 40 40 60 30 DLN 71 47 72 45 / 60 60 60 20 HVR 82 55 81 55 / 20 20 50 50 LWT 75 52 70 51 / 50 70 60 50 && .TFX WATCHES/WARNINGS/ADVISORIES... Numerous flood highlights remain in effect until further notice. && http://www.weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
129 PM MDT THU JUN 21 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1245 PM HAIL 5 SW GREAT FALLS 47.46N 111.38W
06/21/2018 E0.25 INCH CASCADE MT NWS EMPLOYEE
HEAVY RAIN AND PEA SIZED HAIL.
&&
JAAPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
138 PM MDT THU JUN 21 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0104 PM TSTM WND GST 3 WNW SAND COULEE 47.42N 111.22W
06/21/2018 M44 MPH CASCADE MT MESONET
&&
DBPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
139 PM MDT THU JUN 21 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1233 PM TSTM WND GST 6 S GLEN 45.39N 112.68W
06/21/2018 M44 MPH BEAVERHEAD MT PUBLIC
&&
DBPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
140 PM MDT THU JUN 21 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0105 PM TSTM WND GST 21 SW LIMA 44.47N 112.95W
06/21/2018 M42 MPH BEAVERHEAD MT MESONET
&&
DBSpecial Weather Statement National Weather Service Great Falls MT 144 PM MDT THU JUN 21 2018 MTZ053-054-212015- Broadwater MT-Meagher MT- 144 PM MDT THU JUN 21 2018 ...SPECIAL WEATHER STATEMENT... At 144 PM MDT, Doppler radar was tracking a strong thunderstorm near Townsend, moving east at 10 mph. Winds in excess of 30 mph will be possible with this storm. Locations impacted include... Townsend, Silos and Winston. 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. 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. If on or near Canyon Ferry Reservoir, 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 4630 11166 4648 11166 4653 11129 4626 11129 TIME...MOT...LOC 1944Z 268DEG 10KT 4640 11156 JANGLIN
Special Weather Statement
National Weather Service Great Falls MT
201 PM MDT THU JUN 21 2018
MTZ008-015-055-212045-
Madison MT-Beaverhead MT-Gallatin MT-
201 PM MDT THU JUN 21 2018
...SIGNIFICANT WEATHER ADVISORY FOR MADISON...SOUTHEASTERN BEAVERHEAD
AND CENTRAL GALLATIN COUNTIES UNTIL 245 PM MDT...
At 200 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 12 miles southeast of Harrison to near Ennis to
9 miles south of Lima. Movement was southeast at 25 mph.
Dime size hail and winds in excess of 40 mph will be possible with
these storms.
Locations impacted include...
Bozeman, Virginia City, Belgrade, Ennis, Monida, Norris, Big Sky,
Mcallister, Bozeman Hot Springs, Lakeview, Gallatin Gateway, Cameron,
Snowline, Four Corners, Amsterdam, Jeffers, Church Hill, Raynolds
Pass and Monida Pass.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
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 4449 11262 4552 11193 4580 11141 4573 11079
4560 11080 4552 11092 4536 11092 4535 11104
4511 11104 4508 11114 4503 11111 4473 11134
4475 11139 4470 11149 4455 11157 4451 11182
4456 11187 4452 11211 4457 11229 4445 11239
TIME...MOT...LOC 2000Z 321DEG 21KT 4561 11155 4539 11176 4450 11257
JANGLINThe Pocatello radar (KSFX), 243 km away, was scanning. The volume nearest the first event began at 20:08 UTC.
7 thunderstorm wind, 3 hail. Local standard time, as filed.
Mesonet station 2-miles SSW of Cameron recorded 59-mph peak gust from thunderstorm.
Mesonet station in Ennis recorded 65-mph peak gust from thunderstorm.
Mesonet station 22-miles SW of Cameron recorded 58-mph peak gust from thunderstorm.
Mesonet station 5-miles WSW of Big Sky recorded 65-mph peak gust from thunderstorm. Elevation: 8622 feet MSL.
Mesonet station in Boulder reported 58-mph peak gust from thunderstorm.
White Sulphur Springs Airport AWOS recorded 59-mph peak gust from collapsing thunderstorm.
Spotter reported quarter-size hail and wind gusts up to 50 mph from thunderstorm 6-miles ESE of Lewistown.
Facebook video of hail up to quarter-size falling 10-miles WSW of Forestgrove.
Public report of roof ripped off barn by wind gusts from thunderstorm 8-miles W of Forestgrove. Time estimated from radar.
Public reported half dollar-size hail and broken windows on north side of buildings 8-miles W of Forestgrove. Time estimated from radar.
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, June 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: 752031, 752028, 752034, 752027, 752025, 752036, 752038, 752039, 752037, 752040.