This is the first, and probably most important, link that I can find. It is by the person who first really talked about the term Winter Christian; Richard Beck.
A blog post by Richard Beck on his personal site.
The only other substantive thing I have found about being a Winter Christian. The following qoute helps explain a lot in a little bit.
Winter Christians have been injured by their experience of feeling like you must believe in a miracle-a-minute to be a real — REAL! — believer. They recognize that there are people sniffing out the traces of deism everywhere, marking and warning that they don’t really believe in a living, active God. They get the feeling that people wish they just wouldn’t bother coming to the assembly if they aren’t joyful and confident that God is going to do something big. Big!