Wintertime weather inversions are a common occurrence in Montana’s mountain valleys. As high pressure builds, the cold air sinks into the valleys and stays there, resulting in cold, foggy mornings. Usually you have to climb two or three thousand feet above the valley to get out of the inversion: we’ve often left the house on a frigid below zero morning and watched the temperature climb, degree by degree, as we drive up to the top of MacDonald Pass to go skiing. It can be zero degrees and gray in town, and 25 degrees and sunny on top of the pass.
Sometimes, though, the inversion is a shallow one, and I can look out my back door and see that the top of Mount Helena – 800 feet above me – is in the sun, while my house is surrounded by fog. This morning was one of those days, and I walked up the mountain into bright sunshine. It was 10 degrees when I left the house, and 30 degrees on the mountain. How upside down is that?
The fog in the valley, while no fun to live in, is fun to photograph:
Off the Beaten Path: Hikes, Backpacks, and Travels 
I experienced the same thing each fall where we lived in Switzerland. Inversion is called “hoch nebel” (high fog) there, and it could go on for days. Very depressing, especially when you knew just a few hundred feet higher it was sunny and warm and a perfect blue sky. Sometimes I would drive up above the fog just to escape for a while. That ocean of fog below a beautiful clear sky was always beautiful to see (but not to get stuck underneath).
We need to hear more about Switzerland! I know you’ve mentioned it before, but I don’t recall why you were there. And yes, it does get so depressing when the inversions last day after day…after day after day. But today was not a bad one.
Really good photos. I liked the one with the sun above the mountains burning the fog away and shining down on the town.
I think that’s my favorite too.
I’m feeling a little cranky about the fog this morning. Got up at 4:15 for a 6:00 a.m. departure to Phoenix — cancelled because the fog had crept in on little cat feet, as they say. Hope it creeps out before this afternoon.
Looks like it’s maybe creeping out now…I’ll keep my fingers crossed!