Light winds combined with a cold and very moist boundary layer early on the 21sth, which had allowed areas of dense fog to develop over an area that roughly extended from Great Falls to Cut Bank. The Dense Fog Advisories would be cancelled or expire from north to south as the morning wore on as a cold front approached and low to middle level clouds worked against fog maintenance. Once the fog dissipated, the focus then shifted toward a vigorous Canadian cold front that crossed the international border
early in the morning before traversing the remainder of the CWA through the day. Snowfall amounts were generally expected to be in the 3 to 6 inch range for most areas across the plains, with slightly higher amounts in mountain areas and along the
Continental Divide. The Southwest valleys were expected to see the lowest
amounts, with total snowfall expected to be in the trace-3 range. Blowing snow due
to gusty northerly winds was also a concern, especially during the afternoon and evening for areas along and west of I-15 from Helena north to the Canadian border. No changes were made to the existing set of Winter Advisories with the morning forecast. Although areas along the Front had the potential to approach Winter Storm levels at times, it was initially decided to hold off on an upgrade due to a trend for lower snow amounts from model guidance, but the upgrade to a winter storm warning would be made later in the day.

Behind the cold front, temperatures across North-Central Montana were expected to hold in the teens and 20s, but winds and snowfall would make it feel much colder. Temperatures were expected to fall into the single digits to teens across the entire CWA, and there was a possibility for some cold records to be set. Any lingering snow would diminish Thursday morning, but temperatures would struggle to to climb out of the teens across the north and 20s in the southwest.

Winter Weather in BLAINE, MONTANA
From 21-OCT-20 08:00:00 to 22-OCT-20 04:55:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Co-op observer station cnkm8, chinook coop reported 6 of snow.

Winter Weather in MADISON, MONTANA
From 21-OCT-20 16:30:00 to 22-OCT-20 22:30:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reports 1.5 of snow. Visibility under a quarter mile with no wind at time of report.

Heavy Snow in SOUTHERN ROCKY MOUNTAIN FRONT, MONTANA
From 21-OCT-20 13:20:00 to 21-OCT-20 14:20:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Choteau AWOS showed visibility rapidly dropping from 10SM to under 1/4SM in the span of 30 minutes or so, with wind gusts to 30 kts. While the sensor reported FZFG, radar shows a snow band was the likely cause of this.

Heavy Snow in HILL, MONTANA
From 21-OCT-20 07:00:00 to 22-OCT-20 06:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Observer reports 10 of snow.

Heavy Snow in HILL, MONTANA
From 21-OCT-20 07:00:00 to 21-OCT-20 15:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Co-op observer station sipm8 29.9 n gildford reports 6.5 of snow.

Heavy Snow in NORTH ROCKY MOUNTAIN FRONT, MONTANA
From 21-OCT-20 10:00:00 to 22-OCT-20 04:45:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reports 8.2 of snow via Facebook.

Heavy Snow in GALLATIN, MONTANA
From 21-OCT-20 11:00:00 to 22-OCT-20 05:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Cocorahs station mt-gn-11, 1 se bozeman cocorahs reports 7.6 of snow.

Heavy Snow in CASCADE, MONTANA
From 21-OCT-20 15:00:00 to 22-OCT-20 05:56:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reports 8 of new snow overnight.

Heavy Snow in CASCADE, MONTANA
From 21-OCT-20 12:00:00 to 22-OCT-20 12:30:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall total of 11 inches since afternoon of the 21st. Only very light snow at observation time of 12:20. snow water equivalent of 0.56 inches. overnight low of 14 degrees F.