I'm basically thinking of the range below 5C, down to maybe -20C where I give up and drive. There are quite a few mornings where I live which can be 0C, -10C, or -20C, but with no snow or ice on the ground. Plenty cold enough for snow, but none has fallen. Still, the bike lanes tend to be in a less than ideal state, with stuff kicked over there from cars, sand and grit, etc. They do clean them sometimes, but apparently less often than in the summer.