Surface low pressure with an associated warm front and cold front, a highly unstable atmosphere, and strong wind shear all combined to form and sustain multiple severe thunderstorms which moved through eastern Montana during the afternoon and evening of the 29th.
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.
Surface low pressure with an associated warm front and cold front, a highly unstable atmosphere, and strong wind shear all combined to form and sustain multiple severe thunderstorms which moved through eastern Montana during the afternoon and evening of the 29th.
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 Jun 29, 2:24 PM MST, 16 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 324 PM MDT Mon Jun 29 2020 .DISCUSSION... The upper level low currently over Idaho will begin to open up and move northward through the area, then re-close over southern Alberta on Wednesday. Meanwhile, an upper low over northern British Columbia will drop south into Washington by Wednesday, being absorbed by the low in Alberta. This low will drift northward into northern Alberta late in the week, allowing a ridge to build from the Desert Southwest to the Upper Mississippi Valley. This in turn will lead to a southwest flow aloft late in the week, with the peak of the ridging over our area being Friday through Sunday: when the warmest temperatures are expected. Short term (tonight through Tuesday night)... The two main issues in this time frame are the potential for severe weather and heavy rainfall in the eastern parts of the CWA. The SPC has a slight risk roughly east of a Navajo to Terry line, with a marginal risk east of a Glentana to Rock Springs line. The slight risk area looks reasonable given forecast soundings and the fact that the sun is currently (as of 3 pm MDT) out over the SPC's slight risk area, helping to destabilize the atmosphere there. Any storms that do develop will also have the potential to produce heavy downpours, given the high values of precipitable water all across the area and especially there. Gave thought to issuing a flash flood watch in the far eastern zones, but after some internal discussion we opted against it due to the fact that the ground is dry there (but not so dry as to enhance runoff) due to the D0/D1 drought conditions. Flash flood guidance is in the range of about an inch per hour and higher to get flash flooding, which could be hit by an isolated storm but not widespread enough to warrant a watch. Shower/storm chances will begin to decrease from west to east across the area tomorrow, while the east stays wet. Medium/long term (Wednesday through the weekend)... As mentioned above, the upper low will move out and we'll be semi-ridged allowing temperatures to go back up. There will still be disturbances in the flow that help to trigger some showers and storms, but they shouldn't be as widespread as what we're experiencing today. 97 && .AVIATION... FLIGHT CONDITION: VFR/MVFR with occasional IFR. WINDS: NE-N 10-15 kts today, becoming variable this evening and W 5-10 kts overnight tonight. W-SW winds 5-15 kts expected Tuesday. SYNOPSIS: Showers and a few thunderstorms will impact the TAF sites today. Some storms with strong winds and hail are possible at KSDY & KGDV late this afternoon and this evening, tapering off to showers during the late evening and overnight hours. Rain will lower visibilities and ceilings at times to MVFR and occasionally to IFR through tonight. 97 && .GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE. && weather.gov/glasgow
The Glasgow radar (KGGW), 210 km away, was scanning. The volume nearest the first event began at 21:40 UTC.
5 hail, 1 heavy rain. Local standard time, as filed.
Public reported quarter size hail, along with measurements of 49 mph wind gusts and 0.60 inch of rainfall.
Public reported hail up to the size of tennis balls, along with 1 inch of rainfall. Time estimated from radar.
Public reported, via Facebook, that 3.50 inches of rain fell in 90 minutes, at 4 N Raymond.
Trained spotter reported half-dollar size hail. Time estimated from radar.
Trained spotter reported quarter size hail.
Trained spotter reported golf ball size hail.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2020Every state in 2020This day in weather historyWarnings in Montana, June 2020
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: 899341, 899342, 899340, 899343, 899345, 899346.