Wind Makes Clouds on Mt. Rainier

The Venturi effect makes some clouds on the mountain

Video is 15x faster than real life.

I suppose this is not, strictly speaking, a perfect example of the Venturi effect, which applies to fluids flowing through a constricted area—they speed up, and the pressure goes down.

In this case, the wind speeds up to get around the mountain, so it is squeezed in some sense, and the result is the same: the air pressure goes down. Lower pressure means less ability to hold water, so the water condenses into clouds. (The clouds are not always going to form; they only occur if the pressure drop is enough to bring the water out of solution at the new temperature and pressure. This is determined by the adiabatic lapse rate, something pilots deal with regularly. It can get really interesting in mountain passes.)

The Mountain is a pretty major obstacle, so the winds swirl madly, and the sped-up video shows that very clearly.