When your girlfreind is on all fours and your doin her from behind, in the middle of it you swipe her arms out from under her so they're straight out and fuck her till she plows the covers off the bed. Thats the wisconsinsnow plow!
When you're banging a girl from behind, she's holding onto the headboard, and you knock her arms out from under her, her head plows into the headboard, just like a snowplow hits the road.