It's been nearly a quarter of a century since Western Montana has seen an October this dry. 

But that's all going to change suddenly this weekend, so much so, that we could go from sun to snow.

It's not unheard of for the Northwest to get storm protection from a ridge of high pressure in late September and early October. But National Weather Service forecaster Alex Lukinbeal says this ridge has been massive, and stubborn.

"What this pattern does is that it steers us high and dry," Lukinbeal explains. "All the storm systems go well to the north into Alaska and kind of make their way through eastern Canada and these patterns are really persistent. It takes a big mechanism in the atmosphere to change us away from that and as a result of the high-pressure Missoula seeing one of the warmest Octobers on record, currently sitting at the second all-time warmest record October from October 1st to October 16th."

That's pushed temperatures back into the mid-70s this week, even with the cold mornings. That's all expected to change at the end of the week.

Here comes our first dose of winter

It will all start with a dramatic shift in temperatures, and some wind, Thursday into Friday. 

"We're messaging really an abrupt change. You know, temperatures are going to be dropping in one day by 20-25 degrees. We're going to go from, you know, the low 70s all the way down to the upper 40s to low 50s," Lukinbeal says. "And as a result of that we're seeing snow levels dropping below 4000 feet and by Sunday morning, we could be seeing snow all the way down the valley floors."

Maybe an inch of snow on Sunday morning, but more up high. And Lukinbeal says this is probably the end of a memorable fall.

"The warm, dry fall we've been having is abruptly coming to an end. We're not seeing any signs of a big, high-pressure ridge building in behind this. In fact, we're probably going to be seeing another system move in Monday and Tuesday. With high confidence for another mountain snowfall, then it may be some snow in the. valleys as well. If you got any outdoor projects? Probably want to wrap those up by other week 'cause winter is coming."

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