Warm, moist air combined with favorable winds and an approaching low pressure system from the west to form a number of strong thunderstorm across portions of northeast Montana - one of which became severe just before crossing the border into North Dakota.
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 GGW wrote it up.
Warm, moist air combined with favorable winds and an approaching low pressure system from the west to form a number of strong thunderstorm across portions of northeast Montana - one of which became severe just before crossing the border into North Dakota.
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 Glasgow, MT wrote its last area forecast discussion before the first event at May 16, 5:54 PM MST, 4 hours 1 minute earlier.
Area Forecast Discussion National Weather Service Glasgow MT 654 PM MDT Wed May 16 2018 .DISCUSSION... Increased thunderstorm wording a tad for tonight as current activity is threatening the western zones. Another impulse may form over the SE zones around midnight and sweep NE before moving into North Dakota late tonight. Severe conditions are not highly probably, but a couple strong storms cannot be ruled out. TFJ Previous Discussion... Afternoon Update (3pm MDT): No major changes made to the forecast this afternoon. Main focus was on storm system moving through the region overnight tonight through Friday. The forecast for thunderstorms was updated with latest short-term and hi-res guidance. Strong to severe storms will be possible tomorrow as the mesoscale dynamics are expected to line up well with a legitimate hail and wind threat. Otherwise the narrative and the forecast holds well still from this morning. Bigelbach PREVIOUS DISCUSSION: Main forecast challenge remains 2-fold. How high will temperatures reach today, and where will the thunderstorms track later tonight and again Thursday evening? 850 mb temperatures and 500mb height field now shows the current high pressure over our region will retreat toward the SE later today, but will still be able to tap into those higher temperatures lined up along the upper-level ridge axis. Would not be surprised to see a few select locations reach up to touch 90 degrees today, but most other location will likely top out in the upper 80s. The weakened and previously-undercut upper-low now begins to slowly return to the northern Rockies and will arrive over Montana later this afternoon. This disturbance will allow rain showers and isolated thunderstorms to form through central Montana. A few of these could make their way into our CWA tonight. Plenty of instability will be present - CAPE of up to 1000 J/Kg. Thursday, the upper low pressure trough system from the west becomes better organized as the surface low pressure trough slowly moves across E Montana. Instability will be even higher - up to 2000 J/Kg. Forecast afternoon dew points will top out in the mid to upper 50s for some locations. Expect the stronger thunderstorms to break out along this axis of moist and unstable air just east of the surface low pressure trough, but some strong thunderstorms will easily wrap around the backside of this system through Thursday night and should exhaust any remaining instability. Will need to be on careful radar watch for the need to issue any SPS or SVR thunderstorm products. Early Friday morning, we will be in a post-frontal more stable air regime, with any remaining precip being leftover rain showers, which model consensus shows will be gradually diminishing through late Friday night towards the south. Beginning Saturday, high pressure fully returns and brings drier conditions to our region through Sunday. More unsettled weather and thunderstorms will be possible again beginning later next Tuesday. BMickelson && .AVIATION... FLIGHT CAT: VFR. SYNOPSIS: Mostly clear skies and generally light winds will prevail through the rest of the afternoon hours. A storm system moves into the region late tonight, increasing cloud cover and precipitation potential across the sites through Friday. The best chances for thunderstorms, some of which may be strong to severe, over the sites will be in the afternoon and evening hours tomorrow, which may impact operations. WIND: Expect winds to generally be out of the southeast for the period. Wind speeds this afternoon will continue to be in the 5-15 kt range, then back down to under 10 kts tonight and back to 10-15 kts tomorrow afternoon, with higher winds likely underneath any thunderstorms that pass over the sites. Bigelbach && .GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE. && weather.gov/glasgow
Special Weather Statement National Weather Service Glasgow MT 932 PM MDT WED MAY 16 2018 MTZ024-027-170415- Richland MT-Wibaux MT- 932 PM MDT WED MAY 16 2018 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN WIBAUX AND SOUTHEASTERN RICHLAND COUNTIES UNTIL 1015 PM MDT... At 930 PM MDT, Doppler radar was tracking strong thunderstorms near Savage, or 16 miles south of Sidney, moving northeast at 25 mph. Dime size hail and wind gusts up to 50 mph will be possible with this storm. Locations impacted include... Sidney, Savage, Midway, Wooley, Burns and Crane. PRECAUTIONARY/PREPAREDNESS ACTIONS... Frequent cloud to ground lightning may occur with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 4731 10405 4738 10449 4785 10423 4779 10404 TIME...MOT...LOC 0330Z 204DEG 21KT 4748 10423 AEH
Special Weather Statement National Weather Service Glasgow MT 1021 PM MDT WED MAY 16 2018 MTZ017-061-170500- Northern Valley MT-Central and Southern Valley MT- 1021 PM MDT WED MAY 16 2018 ...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL VALLEY COUNTY UNTIL 1100 PM MDT... At 1020 PM MDT, Doppler radar was tracking a strong thunderstorm near St. Marie, or 19 miles north of Glasgow, moving north at 15 mph. Nickel size hail and winds in excess of 40 mph will be possible with this storm. Locations impacted include... St. Marie and Baylor. 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 4838 10638 4842 10668 4873 10662 4868 10622 TIME...MOT...LOC 0420Z 192DEG 13KT 4846 10651 AEH
The Glasgow radar (KGGW), 191 km away, was scanning. The volume nearest the first event began at 04:57 UTC.
1 hail. Local standard time, as filed.
Local fire department officials were responding to a vehicle accident just barely on the Montana side of the border, along Road 327, and reported quarter size hail stones.
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, May 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: 751074.