Believe me, there is NO SUBSTITUTE FOR STUDDED TIRES ON ICE!! I live near Snoqualmie Pass (55 miles e/o Seattle). As you know we get a lot of deep snow, snowplow after-freeze, freeze thaw, crusty ice, ice storms etc., etc. During winter the conditions are always changing from hour to hour. Studless tires are a joke. So you'll need a second set of STUDDED tires & wheels for winter.

Your next consideration is whether or not you also need CHAINS. Chains require a lot of wheel-well clearance, so you couldn't use a big diameter tire if you do. You also need to decide how often you will be driving in DEEP snow. Narrow tires work better than wide in deep snow.

All things considered, I recommend a 235x75xR15 LT. Not too tall or wide and they still leave enough room for chains. Tread pattern is a personnal choice, but STUDDED TIRES ARE IMPORTANT.