Car Shaking

I drive a 97 Eclipse GS coupe with automatic transmissions with about 101,000 miles on it. Last night into this morning we got about 7 inches of snow here in NY and I was driving into town about 15 minutes away, I'd let the car warm up and everything and pulled onto the main road. Got up to 55 mph and the entire car started to shake quite a bit. Let off and the shaking continued until the car was below 45. So I drove about 3 miles into town at 45 with no more shaking until I tried to exceed it. I got into town, went where I needed to and left about 4 hours later. Just to be sure it wasn't one of the wheels, I tried to tighten the bolts, but none of them moved so I'm assuming that isn't it. On the way back I got up to 60 with no problems. Any ideas as to what caused the shaking?

snow probably got caught in your wheel making it off balance

The same thing happens to people where I live, except with mud instead of snow. Go wash your car. :iceslolan