Mountain Flying

Winds Through a Pass

A pass is a venturi. Just as air speeds up through the narrow throat of a carburetor, wind accelerates as it's squeezed through the gap between two peaks — so the breeze in the valley can become a rush of turbulent air in the pass. Narrow the gap, raise the wind, and watch it happen.

Looking straight down · wind flows left → right

valley wind accelerated flow—

Wind approaching the pass15 ktThe valley wind before it reaches the constrictionPass width2,000 ftThe narrower the gap, the more the flow has to speed up

Speed-up

×1.0

vs the valley

Wind in the pass

kt through the throat

In the pass

Flow through the throat

When the forecast winds are much above 20 knots, expect the speed in the passes to be higher still, with turbulence and drafts on the downwind side. Fly to the updraft side of the pass, keep your speed at maneuvering or below, and have a way out that doesn't depend on climbing.