How do car dealerships clear snow off cars...

I worked at a car lot back in the early 90’s in Louisville, KY. My job was one of the “lot boys,” by which we did anything from detailing cars to running personal errands for our bosses in company cars.

When snow fell in increments higher than a dusting, we’d use brooms to push the snow off, then run them through the car wash.

The biggest problem we ran into (unrelated to the OP) was road construction. The lot was right next to a freeway on-ramp. When they were building the ramp, the blocked off the lot’s drainage system on a day when we had torrential rains. The lot FLOODED. I was out trying to move cars to ANY dry spot. The lot sloped toward one end, and, at that point, I was standing in water that came to just under my hips. My personal car was at the lowest part of the lot, and the water was just below my windows.

There exists, somewhere, photos of me SWIMMING in the parking lot.

Before a storm we would park as many cars as we could inside. We put a car on each lift and raised it all the way and park another car under it. The ones that were left outside we would clean the snow off with a snow brush and then wash them in the indoor car wash. The most important part was to get the car completely dry before taking it outside.