A strong area of high pressure over the Great Basin/Rocky Mountain region and a low pressure system dropping south and east into Saskatchewan brought a strong cold front across central and eastern Montana. Very hot temperatures were in place ahead of the front - reaching the upper 90s and low 100s.
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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 GGW wrote it up.
A strong area of high pressure over the Great Basin/Rocky Mountain region and a low pressure system dropping south and east into Saskatchewan brought a strong cold front across central and eastern Montana. Very hot temperatures were in place ahead of the front - reaching the upper 90s and low 100s. Dewpoints were in the 60s and 70s ahead of the front. All of this, combined with strong upper-level winds, provided plenty of instability for severe thunderstorms. By late afternoon, storms began to form and move across northeast Montana with 60 to 75 mph wind gusts. This system moved into North Dakota by approximately 10 PM MDT.
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 Jul 10, 1:30 PM MST, 2 hours 15 minutes earlier.
Area Forecast Discussion National Weather Service Glasgow MT 230 PM MDT Tue Jul 10 2018 .DISCUSSION... The current GOES water vapor loop depicts a shortwave trough over Washington State/British Columbia that is moving east along the International border. This trough will cross the Divide and send a cold front through NE MT late this afternoon and evening. This cold front will find a very unstable environment. With the Heat Index around 100, low-level moisture flowing in from the southeast, upper-level moisture flowing in from the southwest, moderate lapse rates, strong CAPE, an upper air profile with effective shear, strong thunderstorms are expected, some likely severe. SPC suggests the main threats will be very strong, damaging winds and large hail. SPC's Convective Outlook covers the northern half of NE MT with Enhanced risk for Severe Thunderstorms tonight. Initial thunderstorms may develop off high terrain to the southwest. More northerly storms will be associated with the cold front. The separate storm areas will merge this evening along the Northern Tier while moving into North Dakota. KGGW conducted a special upper air run for 18Z. The sounding indicate very strong instability with large CAPE and other convective parameters. As a result, as proposed by SPC, the entire CWA, initially, will be be covered with a Severe Thunderstorm Watch for this afternoon and early evening. Today, the current in-place threat is the Heat Index, which prompted a Heat Advisory for most of NE MT today. This is due to the combination of temperatures in the 90s and Dew Points in the upper 50s to around 70. The advisory is expected to expire around an hour before sunset. Wednesday, will be a cooler day behind the departed cold front and northwesterly flow aloft. Surface winds behind the front may become strong enough to require a Lake Wind Advisory for Fort Peck Lake. Previous Discussion for Wednesday night and beyond: Remainder of the week should be relatively quiet. Temperatures will rebound back into the 90s by Friday. Another upper trof moves across the region through the weekend with a slight potential for thunderstorms with cold front passage Saturday night. Ebert && .AVIATION... Generally VFR conditions expected. This afternoon and evening, restricted flight conditions may occur with any thunderstorms that move through the terminal areas. Strong to severe thunderstorms are expected to be moving across northeast Montana during the late afternoon and evening (approximately 21z to 6z), with the threat highest near the Canadian border. Wind: Very strong wind is expected near any of the severe thunderstorms that develop. Otherwise, expect easterly wind, veering around to the southeast at 10-20kt. After the cold front passes, wind will become northwesterly. && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM MDT this evening for Central and Southeast Phillips...Central and Southern Valley...Dawson... Eastern Roosevelt...Garfield...McCone...Prairie...Richland... Southwest Phillips...Western Roosevelt. && weather.gov/glasgow
Special Weather Statement
National Weather Service Glasgow MT
405 PM MDT TUE JUL 10 2018
MTZ016-022-060-102245-
Garfield MT-Southwest Phillips MT-Central and Southeast Phillips MT-
405 PM MDT TUE JUL 10 2018
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN PHILLIPS AND
NORTHWESTERN GARFIELD COUNTIES UNTIL 445 PM MDT...
At 405 PM MDT, Doppler radar was tracking a line of strong
thunderstorms near Hays, or 11 miles northwest of Zortman, moving
northeast at 40 mph.
Wind gusts up to 50 mph will be possible with this storm.
Locations impacted include...
Zortman, Dodson, Fourchette, Phillips, Wagner, Landusky, Sun Prairie
and Fred Robinson Bridge.
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.
&&
A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
northeastern Montana.
LAT...LON 4792 10863 4799 10861 4798 10844 4845 10841
4844 10840 4843 10835 4850 10834 4855 10808
4763 10764 4761 10851 4762 10852 4761 10858
4763 10870 4792 10875
TIME...MOT...LOC 2205Z 246DEG 35KT 4806 10864
HickfordThe Glasgow radar (KGGW), 128 km away, was scanning. The volume nearest the first event began at 22:47 UTC.
14 thunderstorm wind, 2 hail. Local standard time, as filed.
Malta South US-191 DOT site recorded a 58 mph wind gust.
Trained spotter reported damage to a large rodeo arena and some outbuildings blown down.
Trained spotter estimated wind gusts up to 70 mph.
Saco US-2 DOT site measured wind gusts of 60 mph from 4:32 PM MST to 4:37 PM MST.
Trained spotter estimated hail up to the size of quarters.
Off duty NWS Employee reported large tree branches broken off and estimated 60 mph wind gusts.
Agrimet mesonet site Glasgow 3W recorded a 70 mph wind gust.
Trained spotter estimated 60 mph wind gusts.
Trained spotter measured a 68 mph wind gust.
Mesonet site Lustre 8SSW measured a 60 mph wind gust.
Wolf Point airport ASOS site measured a 58 mph wind gust.
Trained spotter on the east side of Flaxville estimated a 60 mph wind gust.
Mesonet site on the northwest side of Plentywood measured a 65 mph wind gust.
Public reported a tree two feet in diameter twisted, with a few six to eight inch diameter branches broken off.
Comertown Turn-Off MT-5 DOT site measured a 75 mph wind gust.
Trained spotter reported mostly nickel and dime size hail along with a few quarter size hail stones. Time estimated by 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, 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: 773525, 773503, 773504, 773507, 773505, 773508, 773509, 773510, 773513, 773515, 773518, 773519, 773522, 773521, 773523, 773524.