Anytime the temp is below 40 degrees in the morning, you risk seeing ice on road sufaces that the sun hasn't hit yet, especially under an overpass.
I don't believe anyone has mentioned the worst part of winter riding; salt. Unless there has been some heavy rain to wash it away, the first salting is when I usually park my bike. In the northeast, some areas still use a salt/sand/cinder mix. Makes for a scary turn if you don't see it early enough.:11: