A weakening upper level ridge allowed a Pacific weather system to advance into the area. As this occurred, a surface pressure gradient developed along the Continental Divide, with a 23 mb difference between the high over Western Montana and the low over East-Central MT, and this pressure gradient would remain through the day.
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 weakening upper level ridge allowed a Pacific weather system to advance into the area. As this occurred, a surface pressure gradient developed along the Continental Divide, with a 23 mb difference between the high over Western Montana and the low over East-Central MT, and this pressure gradient would remain through the day. This prompted the issuance of High Wind Warnings along the Rocky Mountain Front. Mid and upper level winds would strengthen overnight Monday and into Tuesday as zonal flow became more became more established. This would result in a few scattered high wind gusts across the plains.
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 6, 10:50 PM MST, 3 hours 31 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1050 PM MST Sun Dec 6 2020 Aviation Section Updated. .UPDATE... No significant changes to the forecast this evening. Clear and dry conditions persist across the region tonight under strong high pressure. Overnight temperatures are on track to reach similar values to previous nights, with cold temperatures in SW MT valleys and milder temperatures along the east slopes of the Rockies and plains. Hoenisch && .SYNOPSIS... A brisk westerly flow aloft will develop over the region early this week. The gusty winds will allow for mild afternoon temperatures to continue through Tuesday. It slowly turns cooler starting on Wednesday, along with increased chances for rain or snow showers. && .AVIATION... 1050 PM MST Sun Dec 6 2020 (07/06Z TAF period) VFR conditions continue through the period with some increase in high level clouds expected Monday. West to southwest flow aloft increases later tonight through Monday with breezy conditions developing across north-central MT terminals tonight and increasing winds on Monday. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... With overnight lows falling into the single digits and teens across much of Southwest MT, ice jams could develop on some rivers/streams. The Jefferson River near Three Forks is one river in which gauge readings indicate ice jamming is possible. Thus river highlights might be needed should water levels go into flood stage. Brusda && .PREV DISCUSSION... /ISSUED 422 PM MST Sun Dec 6 2020/ Tonight thru Tuesday...Dry conditions tonight will allow for another good night of radiational cooling across Southwest MT, thus overnight lows similar to last night in that region. For Monday, the high wind watch has been changed to a high wind warning, along with adding Toole county. Wind speeds aloft are just below 70knots. The GFS/NAM do not fully mix down the strong winds aloft, but that potential is there, thus the high wind warning. If the high winds do not develop on Monday, the high wind warning could be cancelled early. Further east, a wind wind watch was issued for Liberty, Hill and Blaine counties for the potential of strong winds on Tuesday. Afternoon temperatures will be close to 20 degrees above normal by Tuesday over North Central MT. No fire highlights at this time, as the duration of the low humidity and gusty winds should generally be less than 3 hours. Tuesday night through Sunday...A weak upper level disturbance will move southward along the divide Tuesday night, producing some light snow. Thus pops increased a bit along the divide for this event. For Wednesday into Thursday, the GFS/EC both have some precipitation over the region. The GFS has been more consistent with the snowfall over Southwest MT, thus pops increased in this region for Wed night into Thu. Some areas could get a 1 to 3 inch snowfall with this event, as of now, that area looks to be along a line from Helena to White Sulphur Springs. The showers decrease a bit for Friday, but another fast moving system approaches the western/southwestern regions in our area, with another potential for rain/snow from Saturday into Sunday. Overall temperatures cool to around seasonal normals across the region from Friday through Sunday. Brusda && .PRELIMINARY POINT TEMPS/POPS... GTF 31 53 41 60 / 0 0 0 0 CTB 27 48 38 55 / 0 0 0 0 HLN 16 46 27 52 / 0 0 0 0 BZN 8 44 18 50 / 0 0 0 0 WYS -10 34 2 35 / 0 0 0 0 DLN 12 43 21 47 / 0 0 0 0 HVR 23 46 34 55 / 0 0 0 0 LWT 25 53 34 60 / 0 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... High Wind Warning from 10 AM Monday to 5 PM MST Tuesday Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky Mountain Front...Toole. High Wind Watch from Tuesday afternoon through Tuesday evening Blaine...Hill...Liberty. && http://www.weather.gov/greatfalls
2 high wind. Local standard time, as filed.
Mdt station at east glacier two medicine bridge measured a 75 mph non-thunderstorm wind gust.
Asos station in Great Falls.
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, December 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: 928051, 928052.