But it was chinook cloud.
What was happening was that I was seeing a diffraction effect, like what happens when you put a stick in clear water and it seems to bend. The warmer air from the chinook was blowing over top of the cold air in the valley and the light was bending as it passed through the varying air densities making it possible for things beyond the horizon to become visible.
So I could see actually see Chief Mountain. But it was a mirage.
And it wasn’t the only one.
Off to the west I could see the land dancing below the mountains, dark lines moving side to side like a bar code as the chinook rolled in. Hills turned from round to square, power poles seemed to grow and stretch upward, cattle walked on shimmering air.
Through the compression of perspective caused by my long lens, I could actually see the varying air densities mixing as I looked toward the Porcupine Hills. The barn in the foreground stayed in focus while the air behind it looked like a mountain stream running over cobbles. I tried for a picture of Chief Mountain but it had already disappeared as the warm air flooded into a different patch of cold.