Strong west-northwesterly flow aloft and a tight pressure gradient associated with a surface trough along a Canadian cold front contributed to strong, gusty surface winds for portions of North-Central Montana.
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.
Strong west-northwesterly flow aloft and a tight pressure gradient associated with a surface trough along a Canadian cold front contributed to strong, gusty surface winds for portions of North-Central Montana.
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 Dec 17, 4:40 AM MST, 1 hour 41 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 440 AM MST Sun Dec 17 2017 ...Aviation Section Updated... .SYNOPSIS... Sunny to mostly sunny skies the morning hours today, will give way to increasing winds and cloud cover by the afternoon. Along the Continental Divide, snow is expected to develop by the late afternoon hours, and persist nearly non stop into the middle of the work week. Significant snowfall accumulations will be possible for areas like Marias Pass over this time frame, which would lead to difficult travel conditions. && .DISCUSSION... Today through Tuesday...main forecast concerns in the short term are snowfall accumulations along the Continental Divide. In addition to accumulating snow during the short term, winds will also be of concern, especially along the Rocky Mountain Front and over the plains of North Central Montana. The short term will begin with a transitory H500 ridge moving overhead during the morning and early afternoon hours today, quickly flattening out as a H500 trough moves across central portions of the Canadian Providences of British Colombia, Alberta, and Saskatchewan this evening and into the morning hours on Monday. Sunny to mostly sunny skies during the morning hours today, will be replaced by increasing cloud cover CWA wide as rich Pacific moisture is ushered in across the Northern Rockies. From 00z Monday to 00z Tuesday, H700-H500 flow will be zonal/nearly zonal from the Pacific Northwest points east across the Northern Rockies, with a H500 speed maximum hugging the US/Canadian border. H700 winds over this span look to peak at around 50-70kts, however, the lack of ridgetops stability gives me some confidence in these higher winds not reaching the surface. Regardless though, a strengthening lee surface trough along the Rocky Mountain Front today will support a period of strong winds from the Rocky Mountain Front and onto portions of the adjacent plains through the early afternoon hours on Monday. The biggest story over the short term will be the persistent snow expected along the Continental Divide. As mentioned early, the extended period of zonal flow will usher in rich Pacific moisture to the Northern Rockies. H700 moisture transport in this evenings model solutions is very impressive from 00z Monday through the day on Tuesday, with PWATs ranging between 0.35" to 0.5", which is about 1 to 2 standard deviations above normal. Given the abundance of moisture and strong upslope flow along the Continental Divide, decided to issue a Winter Storm Warning from 00z Monday until 18z Wednesday. While there will undoubtedly be some lighter intensities in snowfall over this time frame, persistent snow will occur across the Northern Rocky Mountain Front (including over Marias Pass). This persistent snow coupled with the stronger winds (which will lead to areas of blowing snow), will lead to difficult travel conditions. Of greater concern is the expected increase in traffic ahead of the Christmas Holiday across the region. Not to be forgotten, areas of of Central Montana and the mountains of North Central Montana (especially the Bears Paw) will also see snow from Monday through Tuesday. Given that these snowfall amounts are not as high as the current Rocky Mountain Front amounts, decided to hold off on any winter weather headlines for these areas for now. Winter weather headlines will however need to be considered with future forecasts for areas of Central and North Central Montana. - Moldan Tuesday night through Sunday...Only a few days left until the Winter Solstice and medium range models continue to trend toward widespread snow and cold temperatures for mid-week and beyond. Tuesday evening will start off with a strong upper level shortwave trough sweeping inland across the Pacific Northwest Tuesday night. A developing surface low pressure system accompanies this system with a warm front lifting northward across the Great Falls forecast area. Models continue to disagree on placement of the surface low and timing of the Canadian cold front expected to move southward through the region on Wednesday with the ECMWF remaining 3 to 6 hours faster than the GFS. Despite this, there is good enough agreement that I feel confident expecting widespread light snow with temperatures falling through the day as the cold front sweeps southward through the day. Precipitation tapers off from northwest to southeast Wednesday night as the upper trough dives into the Four Corners Region. Meanwhile, a developing storm system in northern Alberta will allow surface winds to become west to southwesterly late Wednesday night and Thursday with mostly dry conditions but continued cold temperatures. For Friday through Saturday, models are in pretty good agreement that this northern system will develop into a deep Hudson Bay low that expands southward across all of the central USA leaving Montana beneath a cold northerly flow aloft. Reinforcing cold high pressure will expand into the region Thursday night into Friday leaving the forecast area with below average temperatures and above normal precipitation through the weekend. mpj && .AVIATION... Updated 1140Z. Pesky IFR/LIFR conditions due to fog are expected at the KBZN terminal through portions of the morning, before finally becoming VFR. Otherwise, VFR conditions are expected at all the remaining terminals for the duration of the 1712/1812 TAF period. Mid- and high level clouds will increase this evening as rich Pacific moisture begins to stream into the region. These mid level clouds may lead to mountain obscuration, especially along the Continental Divide. The biggest story will be the winds across the Rocky Mountain Front and onto the plains of North Central Montana. Winds gusting to 30 to 40 kts are expected at the KCTB, KHVR, and KGTF terminals for today and into the morning hours of Monday. Turbulence due to mountain wave activity will also be possible. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 40 37 46 25 / 10 10 30 50 CTB 40 30 39 18 / 10 10 50 40 HLN 36 29 47 29 / 10 10 30 50 BZN 32 23 45 28 / 10 10 20 40 WEY 20 16 26 20 / 10 20 40 50 DLN 33 26 43 27 / 10 10 10 20 HVR 42 30 40 18 / 10 10 50 30 LWT 39 32 44 23 / 0 10 40 60 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 5 PM this afternoon to 11 AM MST Wednesday Northern Rocky Mountain Front. && http://www.weather.gov/greatfalls
Special Weather Statement National Weather Service Great Falls MT 506 AM MST Sun Dec 17 2017 MTZ055-171400- Gallatin- Including the cities of Bozeman and Gallatin Gateway 506 AM MST Sun Dec 17 2017 ...REDUCED VISIBILITIES DUE TO FOG THROUGH THE MORNING HOURS... Fog, some of which is potentially freezing on contact with road surfaces, is expected to persist into the morning hours across portions of the Bozeman Valley. This includes the Interstate 90 corridor in Gallatin county. In addition to the potential for slick surfaces, visibilities may fall to around a quarter of a mile at times, however, are generally expected to range from around a half of a mile to one mile. Motorist are urged to exercise caution. Use low beam headlights and allow plenty of spacing between vehicles. Moldan
Special Weather Statement National Weather Service Great Falls MT 532 AM MST Sun Dec 17 2017 MTZ009-010-044-046-171400- Northern Rocky Mountain Front-Eastern Glacier-Toole- Eastern Pondera- Including the cities of Browning, Heart Butte, Dupuyer, East Glacier Park, Kiowa, Cut Bank, Santa Rita, Devon, Shelby, Ethridge, Galata, Brady, Conrad, and Ledger 532 AM MST Sun Dec 17 2017 ...REDUCED VISIBILITIES DUE TO BLOWING SNOW... Wind gusts of 50 to 55 mph are causing areas of blowing snow this morning across portions of the Rocky Mountain Front and plains of North Central Montana. Visibilities have fallen to as low as 1 mile at times, especially in areas where recent snow has fallen. This includes the United States Highway 2 corridor from Galata to East Glacier, and Interstate 15 corridor from the Canadian border to approximately Brady. Motorist should be prepared for strong cross winds, especially if traveling on north to south orientated roadways. In addition, motorist should be prepared for reduced visibilities and the potential for slippery roadways. Moldan
5 high wind. Local standard time, as filed.
MT DOT sensor measured peak gust of 86 mph 1 mile ENE of East Glacier Park.
Gleason RAWS, 18 miles WSW of Bynum, recorded peak gust of 64 mph.
Cut Bank Airport ASOS recorded peak gust of 60 mph.
MT DOT sensor recorded 69 mph peak gust 2 miles SE of Browning.
Mesonet station recorded 64 mph peak gust 7 miles E of Geyser.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2017Every state in 2017This day in weather historyWarnings in Montana, December 2017
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: 725888, 725890, 725892, 725889, 725891.