Skywatch Friday: Mountain Weather

We've had some hot daytime weather in the Northern Rockies, and the heat brings some tremendous afternoon storms.

The day begins clear and cool (view west to the Pintler Wilderness from Butte, Montana):

As the heat builds, moisture is drawn up from the valleys. As the air passes over a mountain chain, it cools and builds clouds, and then gets more heat and moisture from the next valley. On a good day, mammotocumulus clouds sweep over the upper valley (Butte sits at the base of the Continental Divide):


And hailstones pelt the earth:


The storm is brief and violent. The clouds pass, the sky clears, and to the east a rainbow appears:

Butte America, lovely weather!