There's many people wondering how many riding days you can get in during the winter. I had that same question last year and marked every day for four months between November 1st, 2008 and February 28, 2009
The criteria I used was: temp above 3 degrees, main roads dry for at least 2 hours during daylight hours.
So, here you go.......
November 16 days
December 8 days
January 8 days
February 23 days
Last year Dec an Jan were the worst for snow that I can remember, so generally I would expect those months to be better. February was unreal... 23 days ... that wasn't a misprint.
So based on those numbers I can justify insuring the bike year round.