A strong and moist westerly flow produces heavy snow over the Northern Rockies. A lee-side low (Alberta Clipper) produces strong surface winds.
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 strong and moist westerly flow produces heavy snow over the Northern Rockies. A lee-side low (Alberta Clipper) produces strong surface winds.
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 12, 8:35 AM MST, 1 hour 15 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 835 AM MST Wed Dec 12 2018 .SYNOPSIS.. Strong winds are expected to continue across much of Southwest and North Central Montana today. Snow will continue along the Continental Divide and over the mountains and passes of Southwest Montana. Travel could be very difficult to near impossible over Western Glacier County, as strong winds and snow combine to create reduced visibility in blowing snow. && .UPDATE... Minor changes to the forecast this morning include dropping POP in downslope areas along the eastern slopes of the Continental Divide. Expect gusty winds to continue through the day across Central Montana. Scattered periods of snow may be seen over Southwest Montana through the day. Expect winds and snow to diminish from the northwest through the day. && .AVIATION... Updated 1215Z. VFR conditions are expected across most of the forecast area through at least 12Z Thursday. Strong westerly winds aloft with the passage of a disturbance will cause significant mountain wave turbulence and occasional low level wind shear at times through the period. These strong winds will likely gust to 70 kt at times along the Rocky Mountain Front throughout the period, but gusts between 30 and 45 kt elsewhere will generally decrease after 00Z. Otherwise, clouds and precipitation (including blowing snow in the mountains) associated with the disturbance will continue mountain top obscuration along the Continental Divide and over southwest Montana (with occasional MVFR conditions at the SW MT terminals - KHLN KBZN KEKS) through around 21Z. Scattered to broken mid level clouds will move over the plains. Coulston && .PREV DISCUSSION... /ISSUED 515 AM MST Wed Dec 12 2018/ Today through Thursday night...primary forecast concerns remain to be 1) accumulating mountain/mountain pass snow from this afternoon through this evening; and 2) strong winds from this morning and afternoon over the plains of North Central Montana and once again along the Rocky Mountain Front and the plains west of Interstate 15 late this evening through Thursday afternoon. Potent open wave which has been bringing the strong winds and mountain snow to Southwest and North Central Montana was just beginning to enter the Northern Rockies region this morning. One new wrinkle with this evenings models has been a fairly potent vort max, which is now prog to drop southeast from Southern British Columbia/Alberta this afternoon and through the early evening hours across North Central Montana. Hi-Res models are rather aggressive with QPF over the Bears Paw, Highwoods, Judith, Moccasin, Little Belts, and Snowy mountains, with generally 0.1"-0.2" of liquid water equivalent. This has led to forecast snowfall amounts of generally 2-4" over these mountain locations. Have refrained from issuing any Winter Weather highlights for Kings Hill Pass and Rocky Boy however, as I am worried about how much dry air is present in the low levels (which would be initially detrimental to precipitation development). Will pass along my concerns to the day-shift, as they will have a better understanding of the low level moisture field once this mornings 12z KTFX sounding is in. Snow has been falling along the Continental Divide and over the mountains of Southwest Montana during the overnight hours, with an additional 2-4" of snow expected at Marias, Chief Joseph, Targhee, and Raynolds Passes, and an additional 1-2" expected for East Glacier and Big Hole Pass. No changes were made to current Winter Weather highlights, but an extension of the Blizzard Warning may be needed. Am most concerned that ground Blizzard conditions may persist despite precipitation intensity decreasing and a slight relaxation in the winds this morning/afternoon. Winds will begin to increase once again this evening along the Rocky Mountain Front, which could produce ground blizzard conditions into the day on Thursday. Winds have generally been gusting between 60 to 80 mph along the Rocky Mountain Front and over the immediate eastern plains overnight. Am still expecting winds to gust upwards of 60 mph over most of the North Central Montana plains this morning and afternoon, however, I am a little concerned that Toole/Liberty/Hill/Blaine Counties may not observe High Wind criteria. Reasoning being is that models have backed off on the H700 flow over the entire region overnight, as well as pushing the strongest winds a bit further south over Central Montana. None-the-less, it will be a very windy day across the region, which will make travel difficult for high profile and light weight vehicles. An extension in the High Wind Warning until 00z Friday for the Northern/Southern Rocky Mountain Front and Eastern Glacier County was made overnight, as winds are expected to reach High Wind criteria again this evening and during the day on Thursday. A brief lull in the very strong winds that were experienced yesterday and overnight are expected from approximately 12pm-6pm today here, but increasing H700 cross barrier flow and strengthening pressure gradient this evening will allow winds to shoot back up again. A further eastward expansion of this High Wind Warning to Toole county may be needed, but held off for now. - Moldan Friday through Wednesday...High pressure will generally drive the weather for the Friday through Sunday. It will keep the area dry and warm on Friday, as temperatures warm up to 10 degrees above normal in the southwest and 10 to 20 degrees above normal over north central Montana. Strong winds could return to the Rocky Mountain Front on Friday as well, but forecast models differ on how strong mid level winds should be, so will stay with a gusty but not strong compromise for now. A weak shortwave trough will then break down the high pressure ridge somewhat Friday night into Saturday. This will cool temperatures to between 5 and 10 degrees above normal, and it will bring a chance of snow to the mountains along the Continental Divide and to a lesser extent into southwest Montana. Gusty westerly downslope winds will keep lower elevations dry. The entire forecast area should be dry with temperatures 10 to 15 degrees above normal Saturday night through Sunday night as the high pressure ridge rebuilds into Montana. Another shortwave trough will move through Montana Monday and Monday night, bringing another chance for mountain snow, along with gusty westerly winds for the plains. In the wake of this disturbance, the jet stream will set up over the Pacific Northwest, Northern Rockies, and Northern Plains Tuesday into Wednesday, between a broad low pressure trough over Canada and high pressure over the Desert Southwest. This could bring another round of widespread strong westerly downslope winds to much of the forecast area with a good chance of mountain precipitation and continued above normal temperatures. - Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 43 26 44 31 / 10 0 0 0 CTB 41 25 43 29 / 30 10 0 0 HLN 41 20 38 21 / 20 10 0 0 BZN 39 13 35 15 / 60 10 0 0 WEY 26 -6 20 1 / 100 10 20 0 DLN 32 7 30 11 / 50 0 0 0 HVR 44 22 45 28 / 60 0 0 0 LWT 38 21 42 28 / 60 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 5 PM MST this afternoon Blaine... Cascade...Chouteau...Eastern Pondera...Eastern Teton...Fergus... Hill...Judith Basin...Liberty...Toole. Winter Weather Advisory until 5 PM MST this afternoon Beaverhead. Winter Weather Advisory until 5 PM MST this afternoon Gallatin... Madison. High Wind Warning until 5 PM MST Thursday Eastern Glacier... Northern Rocky Mountain Front...Southern Rocky Mountain Front. && http://www.weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
823 AM MST WED DEC 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0821 AM SNOW 5 SSE GRANT 44.94N 113.03W
12/12/2018 M1.3 INCH BEAVERHEAD MT TRAINED SPOTTER
.06 IN. OF LIQUID EQUIVALENT.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
832 AM MST WED DEC 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0736 AM NON-TSTM WND GST 7 E MARYSVILLE 46.73N 112.16W
12/12/2018 M44 MPH LEWIS AND CLARK MT TRAINED SPOTTER
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
842 AM MST WED DEC 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0730 AM NON-TSTM WND GST 5 SSE ULM 47.37N 111.48W
12/12/2018 M41 MPH CASCADE MT TRAINED SPOTTER
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
908 AM MST WED DEC 12 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0826 AM NON-TSTM WND GST 6 E MARYSVILLE 46.74N 112.16W
12/12/2018 M57 MPH LEWIS AND CLARK MT TRAINED SPOTTER
&&Special Weather Statement National Weather Service Great Falls MT 919 AM MST Wed Dec 12 2018 MTZ009-014-048-121900- Northern Rocky Mountain Front- Central and Southern Lewis and Clark- Southern Rocky Mountain Front- Including the cities of Logan Pass, Marias Pass, Browning, Heart Butte, Helena, Flesher Pass, Lincoln, MacDonald Pass, Rogers Pass, Bynum, Choteau, and Augusta 919 AM MST Wed Dec 12 2018 Periods of snow with strong gusty winds continue over the Continental Divide this morning. Those driving over Marias, Rogers, and MacDonald passes should be prepared for rapidly changing conditions. Expect strong cross winds, snow covered roads and visibility below one-half mile in blowing and falling snow.
Special Weather Statement...CORRECTED National Weather Service Great Falls MT 922 AM MST Wed Dec 12 2018 MTZ009-014-048-121900- Northern Rocky Mountain Front- Central and Southern Lewis and Clark- Southern Rocky Mountain Front- Including the cities of Logan Pass, Marias Pass, Browning, Heart Butte, Helena, Flesher Pass, Lincoln, MacDonald Pass, Rogers Pass, Bynum, Choteau, and Augusta 922 AM MST Wed Dec 12 2018 .Winter Driving Conditions Over Mountain Passes... Periods of snow with strong gusty winds continue over the Continental Divide this morning. Those driving over Marias, Rogers, and MacDonald passes should be prepared for rapidly changing conditions. Expect strong cross winds, snow covered roads and visibility below one-half mile in blowing and falling snow.
1 blizzard. Local standard time, as filed.
MHP says injury crash. No cause indicated.|MDT Road Report @mdtroadreport.|Blocked southbound lane on US-89 MP 41 at milepost 41.0. roadreport.mdt.mt.gov.|9:50am 12 Dec 2018 MDT Road Report.
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, December 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: 796697.