If the snow cover isn't very thick (just a couple of inches on top of road) a thin tire will cut through it better to get to the road.
There is likely ice under that snow so you need studded tires like these:
http://www.chainreactioncycles.com/ca/en/schwalbe-marathon-w...
Note they come in various widths: down to 35mm (commuting road bike size) to 2 inches (MTB).
I would take these in the 40mm width over the other sizes for commuting in the snow.
If the snow cover isn't very thick (just a couple of inches on top of road) a thin tire will cut through it better to get to the road.
There is likely ice under that snow so you need studded tires like these:
http://www.chainreactioncycles.com/ca/en/schwalbe-marathon-w...
Note they come in various widths: down to 35mm (commuting road bike size) to 2 inches (MTB).
I would take these in the 40mm width over the other sizes for commuting in the snow.