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Check out the comparison of nylon horn covers (like that of which some freight railroads use), and the Amtrak snow cones below.

Below is a shot of my K5LA after the first good snow of 1999.  This shows a small dusting of snow in the K5LA, and my P5LAC completely clogged with snow. The snow cones kept enough snow out so that the K5LA could blow out what was in it, but the P5LAC would not blow at all.