We saw it again last week. Somehow the snow always seems to fall hardest on the main highways through Idaho. Interstate 15 had to be closed from Dubois, Idaho, to the Montana state line last Wednesday thanks to an early fall snowstorm. The storm brought an inch or so of snow to Teton Valley, but there was much more along the main highway corridors. Why is that? How does the snow know to fall where it will disrupt travel the most?
There’s a reason for this; the snow isn’t being intentionally mean to travelers. It probably all began with the game trails that followed the easiest routes through the hills, near the rivers and creeks where the land was low and less steep. Then came the wagon trails and finally the highways following those same low terrain routes.
In the world of weather, we have a thing called a convergence zone. That means a place where winds from different directions meet. When it happens on the uneven surface of the earth, air can flow into a low spot faster than it can flow out. It’s gotta go somewhere, so it goes up, and when you move air up that usually means clouds and storms. We see that all the time on the windward side of mountains or when hot air rises and causes thunderstorms to break out.
During last week’s storm, we had a little battle between the cold air coming down from the north and the warmer air coming up from the south ahead of it. Where they met, convergence zones set up, and the low terrain of the I-15 corridor had more air flowing into it than could flow out. It went up instead, causing heavier snow along the road than elsewhere and eventually closing the highway.
This is just a preview of things to come as winter unfolds. Major highways are often where convergence zones set up and often have heavier snow than the surrounding land. And this always seems to happen on the winter holiday times when people want most to travel on those highways. So this is the time, if you haven’t already, to prepare your vehicle for winter driving and get in the habit of checking the road conditions before you leave on a trip. Conversion zones can happen here in the Teton Basin when the winds are right, or anywhere along your way without warning; they are often small scale events and hard to predict. It’s best to be prepared with the right tires and whatever else you need to be ready for whatever you might drive into out there.