For your conditions it sounds like a tire with a relatively slick center or closely packed knobs with more spaced out knobs towards the edge should work.

Basically the center part would help with rolling while on asphalt, and when you hit snow and your tires sink a little the knobs would help with traction. This of course depends on the type of snow you get.

The WTB Pathway Comp Commuter Tire, WTB Vulpine Dna Mountain Tire, Kenda K-rad MTB Tire looks about right. Or something with an inverse tread pattern like the Continental Town & Country MTB Tire should also work (All found on the Nashbar website).