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Weather Forecast: Winter Storm Sunday into Monday

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Posted at 5:49 PM, Dec 18, 2021
and last updated 2021-12-18 20:09:05-05

MISSOULA — Snow is already falling across northwest Montana this evening. Snow will slide south into west-central and southwest Montana overnight tonight into Sunday.

Accumulating snow will be most likely across northwest Montana Saturday night into Sunday morning. Areas along the Montana/Idaho border Troy, Libby and Trout Creek could pick up 5"-to-10" by Sunday morning. The Flathead and Mission Valleys could see 1"-to-4" and the West Glacier Region picks up 4"-to-8".

The precipitation slides south tomorrow with west-central and southwest Montana picking up most of the snow. Models now have snow stalling somewhere in the vicinity of the I-90 corridor through Monday morning. If this does occur, then a prolonged period of moderate to heavy snow is possible along I-90 from the Idaho/Montana border, east through Missoula. Forecast confidence has increased over the last 24hrs for this scenario to occur. Locations from Saint Regis to Drummond could see around 4-8 inches of snow by the time the event is over late Monday.

Precipitation will fall in the Bitterroot Valley as well, however, confidence for a forecast remains low as models are not in good agreement. Some models have the cold air reaching the Bitterroot Valley leading to higher snow amounts while others keep warm air in place leading to a rain/snow mix and lower snow totals. Right now, the best chance for accumulating snow is Sunday night with 1"-to-4" possible by Monday morning.

By Monday, the snow will retreat back to northwest Montana leading to another round off accumulating snow of several inches for all of northwest Montana.

After a brief brake from the snow Tuesday, a low pressure is expected to takeover the Pacific Northwest for the second half of next week, placing the Northern Rockies under an active weather pattern. This pattern will promote a continuation of mountain snowfall and changeable snow levels with periods of valley snow accumulations through Christmas.