A trough aloft and embedded low pressure center moved slowly east-southeastward over north-central and southwest Montana on June 23rd. Abundant low-level moisture and cold air aloft associated with the trough allowed scattered showers and thunderstorms to develop via daytime heating alone.
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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.
A trough aloft and embedded low pressure center moved slowly east-southeastward over north-central and southwest Montana on June 23rd. Abundant low-level moisture and cold air aloft associated with the trough allowed scattered showers and thunderstorms to develop via daytime heating alone. A nearly-stationary cluster of showers and thunderstorms impacted the Shelby area from late morning through early evening, resulting in excessive rainfall. The Teton River also flooded in Loma. Elsewhere, a non-mesocyclonic tornado touched down near Highwood during the late afternoon. This tornado occurred within a nearly-stationary line of showers and thunderstorms which apparently developed along a low-level convergence boundary. This same line of showers and thunderstorms generated flash flooding in the Bootlegger area, just north-northwest of Great Falls.
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 23, 12:56 PM MST, 1 hour 59 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 156 PM MDT Sat Jun 23 2018 .SYNOPSIS... A low pressure system will bring another round of scattered showers and thunderstorms to the region through Sunday. Some storms could produce brief heavier rain. The passage of this system will keep temperatures below normal through tonight. The showers and thunderstorms will decrease from the west on Sunday with a slight rebound in temperatures, as the system exits to the east. High pressure will bring warming and drying conditions Sunday night into Monday, as temperatures warm to at least 10 degrees above normal. && .DISCUSSION... Tonight through Sunday...Mid to upper level circulation center embedded within a broader upper level trough continues to shift very slowly SE across the forecast area this evening and eventually on into WY Sunday followed by a an upper level ridge building into the Northern Rockies and MT by late Sunday. Scattered to numerous showers and thunderstorms will affect the area through this evening before slowly diminishing overnight through Sunday morning. Storms across northern portions of the forecast area will be in an environment with deeper moisture and slow storm motion, supporting a threat for locally brief but intense rainfall, while storms over SW MT should move quicker with somewhat drier conditions at the surface supporting the threat for gusty winds. Wind shear is marginal at best across the entire area limiting the potential for severe thunderstorms. Some showers and isolated thunderstorms could linger into early Sunday afternoon in northerly flow behind the exiting low with clearing spreading east across the region Sunday afternoon and evening as the upper ridge builds in from the west. Hoenisch Sunday Night through Saturday...The latest forecast model have been fairly consistent with the solution during this period. High pressure aloft in the wake of the weekend system will bring warming and drying conditions Sunday night into Monday, as temperatures warm to at least 10 degrees above normal. A low pressure trough will also move into western North America on Monday, and a Pacific cold front ahead of this system will move into Montana Monday afternoon. The combination of increasing winds aloft and shifting winds with the front could cause increasing wind shear, and the warm temperatures ahead of the front will make for an unstable airmass. As a result, scattered strong storms may develop Monday evening with some showers lingering overnight. A more westerly flow aloft will keep the area dry Tuesday through Wednesday, as temperatures rebound from the cold frontal passage. However, a deepening low pressure trough will bring cooling temperatures and an increasing chance for showers and thunderstorms to the forecast area beginning Thursday afternoon and continuing into the weekend, with the best chance for more widespread shower activity on Saturday. We will continue to monitor this situation to determine just how widespread and heavy the precipitation could be, as there is still some uncertainty in the forecast model depictions. Coulston && .AVIATION... Updated 1800Z. Scattered showers and thunderstorms will become more numerous this afternoon and are expected to continue through this evening before diminishing as an upper level trough shifts east across the region. Brief but intense rainfall and locally gusty winds are the main threats this afternoon and evening.VFR conditions will generally prevail with MVFR and IFR conditions possible in the vicinity of showers/thunderstorms. shift to N/NW flow behind the the low could bring lowering cloud bases and a period of MVFR sailings to KCTB area later tonight. Hoenisch && .HYDROLOGY... As of Saturday morning, rivers generally continue to fall, but water impacting nearby areas will take a bit more time to totally recede or soak into the ground. Therefore, the Warnings will continue for now. Also, scattered showers and thunderstorms this afternoon and evening could bring brief heavy rain, which continues the threat for brief minor additional flooding. Specific County/River situations... Teton County into western Chouteau County...Flood Warning will continue. The Teton River near Dutton has fallen below flood stage as of Saturday morning, but farther downstream near Loma it has yet to fall. Jefferson River...between Whitehall and Trident...Flood Warning continues. The river is still above flood stage, but it is expected to fall below flood stage through the weekend. Fergus County...A Flood Warning is in effect for the Missouri River, especially at the James Kipp Campground. The river level appears to be cresting about halfway between Minor and Moderate flood stage, and it is forecast to gradually fall into early next week. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 55 76 56 88 / 40 20 10 0 CTB 54 77 53 84 / 30 20 10 10 HLN 53 76 53 86 / 40 30 10 10 BZN 47 71 49 85 / 30 20 10 0 WEY 38 65 39 74 / 40 20 10 0 DLN 45 69 47 82 / 50 10 10 0 HVR 57 78 56 88 / 60 30 10 0 LWT 52 69 51 82 / 40 50 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Warnings are in effect until further notice for portions of the Teton and Missouri Rivers in central Montana, and for a portion of the Jefferson River in southwest Montana. && http://www.weather.gov/greatfalls
Special Weather Statement
National Weather Service Great Falls MT
301 PM MDT SAT JUN 23 2018
MTZ012-013-232130-
Chouteau-Cascade-
301 PM MDT SAT JUN 23 2018
...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHEASTERN TETON...
SOUTHWESTERN CHOUTEAU AND NORTHWESTERN CASCADE COUNTIES...
At 301 PM MDT, radar indicated strong thunderstorms were located
along a line extending from 11 miles northeast of Black Eagle to near
Fort Shaw. Movement was south at 15 mph.
Frequent lightning, pea-size hail, gusty winds to 30 mph are
possible with these storms.
Locations impacted include...
Great Falls, Black Eagle, Fort Shaw, Fort Shaw, Portage, Ulm,
Malmstrom Afb, Vaughn, First Peoples Buffalo Jump State Park and Sun
River.
This includes the following highways...
Interstate 15 between mile markers 267 and 296.
Highway 200 between mile markers 131 and 139.
Highway 87 between mile markers 4 and 17.
Highway 89 between mile markers 9 and 16, and between mile markers
90 and 8.
Torrential rainfall is also occurring with these storms, and may
cause 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.
LAT...LON 4756 11094 4731 11184 4759 11189 4761 11177
4761 11168 4763 11167 4773 11115
TIME...MOT...LOC 2101Z 345DEG 11KT 4766 11115 4746 11177
CCSpecial Weather Statement National Weather Service Great Falls MT 320 PM MDT SAT JUN 23 2018 MTZ012-013-232200- Chouteau MT-Cascade MT- 320 PM MDT SAT JUN 23 2018 At 316 PM MDT, Doppler radar was tracking strong thunderstorms along a line extending from 10 miles northwest of Highwood to near Fort Shaw. Movement was south or southwest at 5 to 10 mph. Frequent lightning, torrential rainfall, pea-sized hail, and gusty winds are likely. Localized flash flooding may also be possible in poor drainage areas. Locations impacted include... Great Falls, Black Eagle, Fort Shaw, Fort Shaw, Floweree, Portage, Ulm, Vaughn, First Peoples Buffalo Jump State Park, Sun River and Malmstrom Afb. 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 4765 11071 4735 11176 4751 11184 4779 11080 TIME...MOT...LOC 2116Z 349DEG 6KT 4772 11088 4748 11173 CC
The Great Falls radar (KTFX), 48 km away, was scanning. The volume nearest the first event began at 21:53 UTC.
2 flash flood, 1 tornado, 1 flood. Local standard time, as filed.
Storm chaser recorded video of non-mesocyclonic tornado near Highwood around 3:55 PM MDT. This tornado lasted about 5-minutes. No damage, injuries, or deaths reported. Location and path of tornado estimated via radar. Width also estimated.
Home weather station 8.5-miles NNW of Great Falls reported 4.64-inches of rain in four-hours ending at 6:54 PM MDT, with 3.70-inches of rain falling in only one-hour between 2:58 and 3:58 PM MDT. NWS employee observed flash flooding and severe erosion in the same area.
Facebook video of flooding along Teton River in Loma. Apparently runoff from nearby and nearly-stationary showers and thunderstorms caused the river to overflow its banks.
Facebook video of flash flooding at and near the US-2/I-15 interchange in Shelby. Some cars stalled in the floodwater.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2018Every state in 2018This day in weather historyThe tornado archive for Montana, 2018Warnings 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: 752049, 752326, 760593, 752048.