[Eric A. Taylor (OP)]

Today (14 Dec) a tornado struck in a small town about 40 miles south of where I live (Near Portland, Oregon) It's been fairly cold all week. I thought tornado needed warmer weather to form.

Tornadoes require quite a lot of energy to get going and are extremely rare in Oregon. To be honest I think more about the threat from "the big one" that everybody is talking about. I've always thought that to get a tornado you need to have a super cell, and to get that you need heat. So how do you get a twister when it's cold?

[SeanB]

You do not need heat, you need a temperature difference that enables the formation of clouds, and if the topography is right you will have the possibility of a tornado forming.