What is your commute like? West hills, or banana belt down low? Troutdale? Do you absolutely, positively have to get to work on your schedule, or can you take a personal day when the roads are at their worst?
I've found that "just cold" and summer tyres are ok. DO NOT expect much stick. It's the frozen white stuff that can do you in here.
P.S. The air temp may have been in the 40 F range lately in the early am, but the ground is still plenty warm. Don't be lulled into a false sence of security. January can be a whole different game.