An amplified and positively-tilted longwave trough moved eastward over North-Central and Southwest MT. Isentropic lift of warm, moist air over an arctic air mass occurred ahead of the trough, allowing widespread light to moderate snow to develop over the region.
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.
An amplified and positively-tilted longwave trough moved eastward over North-Central and Southwest MT. Isentropic lift of warm, moist air over an arctic air mass occurred ahead of the trough, allowing widespread light to moderate snow to develop over the region. Low-level northwesterly to northerly upslope flow enhanced this snow along the north aspects of the Big Belt, Little Belt, and Big Snowy Mountains near Great Falls and Lewistown. In addition, mesoscale bands of heavier snow impacted portions of Southwest MT in association with low- to mid-level frontogenesis ahead of a shortwave trough embedded within the aforementioned longwave trough. The bulk of snow during this event fell between Thursday, December 15th and the morning of Friday, December 16th. Many locations reported storm-total snowfall in the range of 3 to 12-inches.
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 15, 10:30 AM MST, 5 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1030 AM MST Thu Dec 15 2016 ...AVIATION SECTION UPDATED... .UPDATE... Most of the forecast for the rest of today remains valid. A low- to midlevel shortwave trough will continue to approach our CWA from the Pac NW and southern BC. Thus, expect periods of primarily light to moderate snow to persist the rest of today. Brief bursts of heavy snow within narrow snow bands are expected in portions of Central and Southwest MT per latest mesoscale model guidance. These bands will stem from low- to midlevel frontogenesis amidst abundant moisture. Over this portion of the CWA, a nearly- stationary front separating arctic air to the north from milder air to the south is expected to persist through at least sunset. Through nightfall this evening, expect additional snowfall to generally be 1-3 inches on the North-Central MT plains, 1-4 inches in Southwest MT valleys, and 3-8 inches in the mountains, especially those in Central and Southwest MT. Jaszka .DISCUSSION... Thursday through Saturday...Latest upper air analysis shows a positively tilted trough extending from the eastern Pacific NE into SW Canada. Ahead of this trough, a strong 120kt+ jet is bringing seasonally high moisture into the northern half of the western US. Locally, widespread light snow has developed along/south of a line from Missoula to Helena to Livingston. This snow appears to be primarily driven by broad warm air advection (WAA)/isentropic lift ahead of the upper level trough. The WAA/isentropic lift should allow light snow to continue to move NE through the remainder of the CWA through the morning hours, with snow continuing through Thursday night, before tapering off from north to south on Friday. The overall evolution of the system hasn't changed much, but there are a few things worth noting. 00Z model guidance is now suggesting a dry slot may cut across parts of central Montana Thursday afternoon as the mid-level flow turns more westerly. This combined with some potential downsloping effects, due to the westerly flow, may limit snowfall coverage/intensity for part of the day Thursday across central and western sections of central Montana. Whether this pans out or not remains to be seen, but this may ultimately cut down on snowfall amounts from Cut Bank to Great Falls and the latest snowfall forecast reflects this potential. At the same time, the low/mid level flow eventually turns more northerly by Thursday evening which may allow for some upslope enhancement north of the central mountains and may offset the drying aloft noted in the models, at least near/south of the Great Falls area. Therefore, for those areas, snowfall amounts were trended down some, but not too much due to the uncertainties. For the system as a whole, the models continue to point towards the best lift located across the southern half of the state. It is in this area that some mesoscale enhanced snowfall rates will be possible, but may ultimately be determined as the event unfolds. So, while a general 4-8" is expected at lower elevations of SW MT, isolated higher amounts will certainly be possible if any mesoscale banding develops. Of note, too, there may be a brief lull in the heavier/steadier snow Thursday night across SW MT, but a second area of enhanced lift may bring an additional round of steadier/heavier snow on Friday. For now, left the current Winter Storm Warning in this area as is, but later shifts may need to extend it further into Friday. It is expected that the greatest likelihood of significant impacts with this system will be across SW MT, with somewhat lesser impacts as you go further north. That said, significant impacts are still likely across parts of central Montana, especially southern sections, but potentially not as widespread as further south. For this reason, will keep the current Warnings/Advisories for central Montana the same, but will closely monitor if any northward adjustment in the advisory is needed for the remainder of the Hi- Line. In the wake of this system, the models continue to bring in significantly colder temperatures by Friday/Friday night. The fresh snowcover should help with lows bottoming out well below zero, but the wind may prevent the coldest temps from being realized. Either way, it is likely that much, if not all, of the area will at least need a Wind Chill Advisory for Friday/Friday night. Martin Saturday night through Thursday...Medium range models continue to show agreement for the weekend but their solutions diverge significantly by early next week. Period starts off with an upper level trough moving away from the state with downslope winds developing east of the Continental Divide. The combination of Chinook winds and increasing atmospheric thickness values will allow temperatures to warm back towards seasonal averages for the early portion of next week. Northwest to west flow aloft will continue to bring accumulating snows to the mountains along the Continental Divide while only isolated light snow showers move out over the plains Sunday through Monday. Models also agree that an upper level disturbance will across northern Montana Monday night but beyond this time period significant differences arise mainly due to timing and strength of shortwave activity in the flow aloft. At this time it appears that high temperatures on Tuesday will be the warmest seen in several weeks with gradual cooling expected each day beyond that. Also, with west to northwest flow aloft over the region, have kept PoPs in place over the western mountains with lower elevations trending back toward climatological PoPs from mid-week onward. MPJ && .AVIATION...Updated 1730Z. An upper level low pressure trof is moving over the West Coast and moisture ahead of this system is moving through Nevada, Southern Idaho, and into Southwest Montana. Periods of snow will continue across Central and Southwest Montana through Friday with widespread MVFR/IFR conditions and mountain obscuration. && .PRELIMINARY POINT TEMPS/POPS... GTF 8 -5 -4 -19 / 80 50 40 20 CTB 3 -11 -7 -23 / 70 60 40 10 HLN 13 -5 -2 -20 / 90 60 50 20 BZN 26 3 7 -19 / 80 90 70 20 WEY 30 12 17 -32 / 100 90 80 30 DLN 35 6 7 -16 / 40 60 70 20 HVR 9 -5 -2 -20 / 70 60 40 10 LWT 14 -7 -4 -24 / 60 50 50 30 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 6 AM MST Friday Cascade...Central and Southern Lewis and Clark...Eastern Teton...Fergus...Judith Basin...Meagher...Southern Rocky Mountain Front. Winter Storm Warning until 6 AM MST Friday Beaverhead... Broadwater...Gallatin...Jefferson...Madison. Winter Weather Advisory until 6 AM MST Friday Chouteau...Eastern Glacier...Eastern Pondera...Northern Rocky Mountain Front. && weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
817 AM MST THU DEC 15 2016
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 AM SNOW 3 WNW EAST HELENA 46.61N 111.96W
12/15/2016 M3.5 INCH LEWIS AND CLARK MT ASOS
3.5 INCHES OF NEW SNOW SINCE MIDNIGHT AT HELENA
AIRPORT.
&&
KJPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
952 AM MST THU DEC 15 2016
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0901 AM SNOW LINCOLN 46.95N 112.68W
12/15/2016 E4.0 INCH LEWIS AND CLARK MT AMATEUR RADIO
HAM RADIO REPORT OF 3 TO 4 INCHES OF NEW SNOW SINCE
SUNSET ON DEC 14TH.
&&
KJPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1004 AM MST THU DEC 15 2016
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0729 AM SNOW 2 N CLANCY 46.49N 111.99W
12/15/2016 E4.0 INCH JEFFERSON MT PUBLIC
FACEBOOK REPORT OF 4 INCHES FOR STORM-TOTAL. STILL
SNOWING AT THE TIME.
&&
KJ8 winter storm. Local standard time, as filed.
MT DOT reported I-15 closed at Capital Interchange in Helena due to semi truck stuck on the southbound exit ramp. DOT also reported snow and ice on area roadways at the time.
Two-vehicle accident with vehicles off roadway per MT DOT. MT DOT also reported snow-covered roadways at time of accident.
MT DOT declared snow chains required for towing units on I-15 between Boulder Hill and Clancy (i.e. between mile markers 171 and 182).
KFBB-TV reported that the Great Falls Police Department had responded to 25 different vehicular accidents since 6 AM MST December 15th. Some accidents involved injuries, but number and types of injuries were not reported.
KBZK-TV reported that the Friday evening, December 16th boys and girls high school basketball games in Bozeman were postponed.
KBZK-TV reported the Twin Bridges vs. Ennis boys and girls high school basketball games for Friday evening, December 16th, had been postponed.
KBZK-TV reported the Lone Peak at White Sulphur Springs boys and girls high school basketball games for Friday evening, December 16th, had been postponed.
MT DOT declared snow chains required for towing units on Homestake Pass along I-90.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2016Every state in 2016This day in weather historyWarnings in Montana, December 2016
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: 662908, 662925, 662910, 662926, 662928, 662930, 662931, 662913.