I'm going to be driving with my wife and two children from Minneapolis to Seattle during a week between Jan 2 and Jan 9 next year. I'm planning on spending at least of couple of days in Yellowstone but other than that am fairly open about the itinerary. We are in no rush to cross the mountains but we do have to get to Seattle by the 9th. I've been just assuming that as long as we listen to the weather reports and don't head off into a potential storm, that we'll be fine driving around and across Western Montana and Idaho. But are major highways often closed or impassable? Does I-90 ever shut down entirely?

-Chris

In Western Montana I-90's elevations go up to over 6000 ft (at the continental divide) and around that at Lookout Pass at the Idaho line. From there it falls, then climbs to around 3000 ft. at Snoqualmie Pass an hour east of Seattle.

Coming from Minnesota I'd assume you're cool with winter driving conditions. I'm not certain of the Montana high places, but do know that Snoqualmie Pass occasionally closes in the winter for avalance control, thereby shutting down the road for a few hours at most (typically).

Frankly I'd be more concerned with crosswinds and icy conditions in Eastern MT and the Dakotas than with snow in the mountains.

Have fun and good luck.

That's avalanche.

It's extremely rare for mountain passes on I-90 in Montana and Idaho to be closed. But not unheard of. I have been delayed a few hours because Lookout Pass (Mont/Ida. border was closed because of heavy snow. Knew that in advance and waited it out in C.d'A. Another time had to sit for a couple of hours in my car because of a truck accident on the east side of Lookout Pass. You will have chains, I assume, which some times are required, particularly on Snoqualmie Pass.

I had heard that chains were a good idea. I'll consider them required on the strength of your advice.