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: