The recent fall thaw is about to give way to a sharp November nip.

Snow levels across western Montana are expected to drop to about 5,000 feet by Wednesday, ushering in more seasonal temperatures and periodic mountain snow.

By the weekend, residents in the Flathead Valley could be shoveling.

“This will be a significant shock to the system and likely the first widespread, low-elevation winter impact of the season,” the National Weather Service in Missoula said in its Sunday forecast.

Looking further ahead to Thanksgiving week, travel could be tricky as a surge of moisture targets the Pacific Northwest and temperatures fall.

Meteorologist Alex Lukinbeal said most models point to an atmospheric river making landfall by Nov. 22.

“It’s just a question of where it is going to be focused,” he said in a Sunday briefing.

If the low-pressure system drifts north, impacts on Northwest Montana would be reduced. Still, winter weather is likely. High temperatures in valley locations during Thanksgiving week are expected to stay below freezing.

“How much snow falls in the valley remains to be seen, but the dice are definitely loaded toward travel disruptions with winter conditions,” Lukinbeal said.