Originally Posted by kbryce
I just don't want to buy tires, have them put on, then have another winter like last with one day of snow.
This is definitely the biggest misconception about winter or "snow" tires, that their only benefit is traction in snow and other frozen precipitation. Their real (and most important advantage, unless you're living in Calgary or some other place that's covered in snow for most of the winter) is cold weather traction and braking. Ambient temps under 45f will give a dedicated winter tire a decided advantage (I've found this to be closer to 50f, especially when compared to dedicated summer-only tires), and ambients around freezing or below just make summer-tire use dangerous. All-seasons are bordering on dangerous around freezing as well, and this is without any precipitation entering the equation.
In your area I'd imagine the aggregate ambient temps hover around 40f and below from late Nov-March and beyond, you'd be much safer on winter tires. Costs would be roughly similar to running an all-season with a tread-life of 300-400, as you'd be splitting duty and running each system for half a season.
I'm in Seattle and have ambients around 45f for most of the winter with a very occasional snow event, having winter tires is safer even in that environment, and when I want to go to the mountains or a snow event happens, I'm able to get about.
I just put a set of the new Dunlop Winter Sport 4Ds on the E91, I have yet to see how they perform in precipitation but they're amazing in the dry at 55f and below. Very difficult to tell that they're a winter tire, they handle amazingly well (though I do have 225/40/18s). I have the Winter Sport 3Ds on a FWD Saab 9-5 Aero wagon, and those are amazing tires as well.