Winter Cloud Tops

This is somewhat related to the optimal altitudes question, but I
thought I would start a new thread here...

What are the typical cloud tops at for winter flying--if there is any
such thing as typical. I would venture to guess that tops are below
10,000 ft 80% of the time. I am talking here about mid-west and east
coast. I am particularlly interested in the Wisconsin-to-D.C. flight
path, if folks have direct experience with that particular one.

It sure would be nice if there was a historical weather data
(particularly on tops) that pilots could go research.

-Sami