You start getting impaired thinking? I think the decision to go out in January, with temps below zero, involve impaired thinking from the get go.:) Not that I would do that solo in CA.
You need to look at the wintertrekking website
www.wintertrekking.comThose guys are out in -40C and think you're a wussy if your limit is -20C. Btw, no UL on that site.
PS. Good job Andi! Really valuable info.