An upper level trough moved through Montana for Sunday April 18th. As it did so, it brought a cold front and associated moisture through the area, which resulted in rain that quickly turned to snow as colder air arrived.
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 upper level trough moved through Montana for Sunday April 18th. As it did so, it brought a cold front and associated moisture through the area, which resulted in rain that quickly turned to snow as colder air arrived. While most of the area received light snow (generally about an inch or less), areas prone to upslope snow showers along the Rocky Mountain Front and along the north slopes of the Little Belts and Snowy Mountains. A few areas received over 6 of snow with this system, which combined with the icy roads, resulted in a few accidents, including one that blocked Rodger's Pass for a few hours while crews removed a jackknifed tractor trailer.
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 Apr 18, 11:15 AM MST, 1 hour 45 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 1215 PM MDT Sun Apr 18 2021 Aviation Section Updated. .SYNOPSIS... A strong cold front will move through north central Montana today, then through central and southwestern Montana overnight. Expect rain to quickly transition to all snow late this afternoon. Accumulating snow will affect much of the forecast area tonight and Monday with residual showers lingering through Tuesday. Dry and warmer conditions are expected Wednesday and Thursday before the next weather system arrives Thursday night. && .Morning Update... Cold front surging south from Canada has or was beginning to cross the International Border as of this update, with areas west of the I-15 corridor already seeing a wind shift to the northwest and an increase in speeds due to a strengthening barrier jet here. Precipitation has generally been trailing the initial wind shift associated with the cold front by 1-3 hours as it has moved south across Canada, and I expect this trend to continue further south across our CWA. Most areas across North Central and Central Montana should therefore expect precipitation to begin within this 1-3hr period following the wind shift to the north to northeast. Rain is expected to be the primary precipitation type initially; however, a transition to rain/snow or all snow is expected within 1-2hrs of the initial onset of precipitation as the column quickly cools. Will be re-evaluating winter weather highlights, mainly along the Montana Hwy 200 corridor, over the next several hours for the potential need to upgrade given potential impacts to travel and power infrastructure. My intention is to give another update around the noon hour prior to the afternoon package issuance with latest thinking on highlights and potential impacts. - Moldan && .AVIATION... 1215 MDT Sun Apr 18 2021 (18/18Z TAF period) A cold front moving north to south has moved through N-central MT and is continuing southward. Lower MVFR ceilings are filling in quickly. Expect precipitation to start off as rain with IFR/MVFR conditons before turning over to all snow during the mid to late afternoon and evening for widespread LIFR/IFR conditions. Snow continues overnight before diminishing Monday morning. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 525 AM MDT Sun Apr 18 2021/ A vigorous upper level shortwave and associated surface cold front will sweep southward from Canada today. This system will bring an increasing likelihood for rain which will quickly turn over to snow as much colder temperatures move into the state. Winter Weather Advisories remain in place for portions of north central, central, and southwestern Montana through Monday morning. Snow accumulations will mainly impact the mountains and favored upslope areas adjacent to the Rocky Mountain Front and the central Montana island ranges. Anywhere from 5 to 10 inches (possibly as much as a foot) of snow accumulation is likely in the mountains, with lower elevations seeing snow totals ranging from 1 to 6 inches in the upslope areas. Other locations over the plains will only see a trace to an inch or two of snow. Warm temperatures today will limit snow and ice accumulations on roadways, but much colder temperatures and steady light to moderate snowfall will create icy conditions overnight into Monday morning. As mentioned above, the heaviest precipitation should diminish Monday morning but continued cold and unsettled conditions will allow areas of light snow to persist into Tuesday. Skies will clear out late Tuesday with temperatures rebounding back to seasonal averages on Wednesday. Diagnostic models and ensembles continue to trend toward bringing several weak weather systems through the region Thursday through Sunday. However, confidence in timing, location, and amounts remains fairly low. Best bet for this time period will be for temperatures to oscillate above and below seasonal averages as each system moves through the state. PoPs currently remain at slight to medium chance (20 to 40 percent) for lower elevations with chance to likely PoPs (30 to 60 percent) in the mountains. QPF/snow amounts appear to be generally low for now. mpj && .PRELIMINARY POINT TEMPS/POPS... GTF 51 22 35 22 / 100 100 30 10 CTB 43 20 36 21 / 100 100 10 0 HLN 60 26 36 23 / 80 100 20 0 BZN 62 25 36 18 / 60 100 60 0 WYS 53 19 32 10 / 40 60 60 0 DLN 63 25 36 16 / 20 100 70 0 HVR 42 22 39 24 / 100 60 30 0 LWT 50 20 31 19 / 100 100 70 20 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 PM this evening to noon MDT Monday Broadwater...Gallatin...Jefferson...Meagher. Winter Weather Advisory from 4 PM this afternoon to noon MDT Monday Cascade...Central and Southern Lewis and Clark...Fergus... Judith Basin. Winter Weather Advisory until 3 AM MDT Monday Eastern Glacier... Eastern Pondera...Eastern Teton...Northern Rocky Mountain Front...Southern Rocky Mountain Front. && http://www.weather.gov/greatfalls
Special Weather Statement National Weather Service Great Falls MT 113 PM MDT Sun Apr 18 2021 MTZ009>013-044>051-182100- Northern Rocky Mountain Front-Eastern Glacier-Hill-Cascade- Chouteau-Toole-Liberty-Eastern Pondera-Blaine- Southern Rocky Mountain Front-Eastern Teton-Judith Basin-Fergus- Including the cities of Logan Pass, Marias Pass, Browning, Heart Butte, Cut Bank, Havre, Rocky Boy, Rudyard, Great Falls, Cascade, Belt, Kings Hill Pass, Fort Benton, Carter, Big Sandy, Shelby, Sunburst, Chester, Whitlash, Brady, Conrad, Chinook, Harlem, Hays, Bynum, Choteau, Augusta, Fairfield, Dutton, Raynesford, Stanford, Hobson, Lewistown, Winifred, Lewistown Divide, and Grass Range 113 PM MDT Sun Apr 18 2021 ...Rain and snow will develop by this evening... At 1 PM, rain and snow were falling along the Highway 2 corridor from Cut Bank to Harlem. This area of precipitation was moving to the south around 25 mph. The rain will change to snow generally in one to two hours after it begins. Expect visibility to be reduced to less than one mile at times in areas of snow. Wind gusts of 35 to 45 mph will are also expected. Those traveling this afternoon and into the evening hours over North Central MT should be alert for quickly changing road conditions and areas of poor visibility. MTZ008-014-015-052>055-182100- Beaverhead-Central and Southern Lewis and Clark-Madison-Jefferson- Broadwater-Meagher-Gallatin- Including the cities of Big Hole Pass, Wisdom, Dillon, Chief Joseph Pass, Monida Pass, Wise River, Helena, Flesher Pass, Lincoln, MacDonald Pass, Rogers Pass, Ennis, Norris Hill, Raynolds Pass, Twin Bridges, Virginia City, Montana City, Boulder, Boulder Hill, Elk Park Pass, Homestake Pass, Whitehall, Toston, Townsend, Winston, Martinsdale, Deep Creek Pass, White Sulphur Springs, Bozeman Apt, City of Bozeman, West Yellowstone, Battle Ridge Pass, Bozeman Pass, and Targhee Pass 113 PM MDT Sun Apr 18 2021 ...Cold front with gusty winds to move through this afternoon... At 1 PM, a strong cold front is beginning to move southward through Southwest MT. Expect falling temperatures this afternoon, along with a period of gusty winds as the cold front moves through. Wind gusts between 35 and 45 mph are expected along the cold front. These gusty winds could cause some impacts to those recreating on area lakes and rivers. Rain and snow will develop late this afternoon and into the evening hours, as the cold front moves further south. Brusda
10 winter weather, 4 heavy snow. Local standard time, as filed.
Snow had mostly stopped by 9pm last night. most of the accumulation occurred during the day.
Trained spotter reports 5 inches of snow.
Trained spotter reports 5 inches of snow.
Public reports 4.5 inches of snow.
Lincoln volunteer fire department estimated between 6 to 12 inches of snow at rogers pass. Semi jackknifed on the pass. Significant drifting of snow.
Public reports 7.5 inches of snow.
Trained spotter reports 3.5 inches of snow.
Trained Spotter reports 5 inches of snow.
Co-op observer station snrm8 sun river 4s coop reports 4.5 inches of snow.
Trained spotter reports 4 inches of snowfall.
NWS employee reports snowfall of 6.8 inches. Snow began about two hours before it began to accumulate (start time of accumulation is used as start time).
Trained spotter reports 4 inches of snow.
Social media report of 4 inches near Church Hill.
Cocorahs station mt-bv-22 glen cocorahs reports 3.2 inches of snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2021Every state in 2021This day in weather historyWarnings in Montana, April 2021
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: 943542, 943565, 943567, 943572, 943533, 943539, 943590, 943560, 943573, 943575, 943556, 943582, 943584, 943593.