How do snow fences work?

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How do snow fences work?

snow drift covers pole of stop sign

Snow fence might not have helped here (Ottawa, Canada).

Snow carried by wind can reduce visibility and cover roads. We cannot “switch off” the wind; but we can slow it with obstacles. Obstacles like trees and fences break wind into a swirl of eddies, reducing its overall speed. This is why a wooded, fenced-in suburb is generally much less windy than a lake shoreline.

Snow fences use this concept to keep snow from blowing across roadways. Snow flying on high winds past a snow fence will get caught in the turbulent eddies created by the fence. As the air slows, it will drop some of the snow just beyond. Eventually a large pile of snow can accumulate downwind of a snow fence.

If the fence is located upwind of a road, the snow collects around the fence and doesn’t drift onto the road. If the fence were too close to the road, some of that snow would drop onto the road and cause traffic problems. Optimally, the fence should be set back about 35 times its height from the road, so a two foot fence should be placed about 70 feet upwind from the road.

Snow fences work best when they are placed on a long open expanse upwind of the road, and the wind blows mostly from one direction.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.