Last night I went for a run outdoors, in homage to CG.
I figure that to not go outdoors because it is "cold" is just plain wimpy, I should be GLAD for the fact that I can run at all.
It was 6F at the time, I wasn't wearing much, and I sweated my bag off. I know about cold, so I piled it on my neck, head, and hands.
I roasted like you wouldn't believe.
It's been really cold here lately, around -10 or -15F, but there really isn't any snow. With that experience last night, and with temps forecast in the 20's this weekend, I'm seriously thinking of starting some outdoor sprint drills at the track...with wool socks and my larger trainers, of course.
Maybe slowly and gingerly, to avoid shin splints.
I would say that there is a step function at around -20C, below which it actually feels cold, and where wind chill (even just from running), can get nasty.