I couldn't pass up a deal on a set of extra wheels when I picked up my new forks so I think I'm gonna try a set of knobbies on them for when the snow flies. Think a set of Kenda dirtbike tires would suffice? 90/90-15 rear 70/100-19 front.

Front:
http://www.motorcycle-superstore.com/2/29/391/5073/ITEM/Kenda-K771-Millville-...

Rear:
http://www.motorcycle-superstore.com/2/29/391/5072/ITEM/Kenda-K771-Millville-...

I'd prefer it be narrow, it needs to cut down into the snow to either bite or (hopefully) reach the ground. The wider the tire, the more it floats and the less traction you get - true with any tire. When it snows here, it snows. We get what's known as "lake-effect" where the warm lake water feeds the storm cell and dumps a lot more snow than surrounding areas. Cities of Western/Upstate NY have the highest averages of snowfall in the country(including Alaska), averaging around 100" per season.

http://www.city-data.com/top2/c464.html