Wow.
It was 23C earlier today where I'm at. I remember seeing snow once but can't for the life of me remember if it was one or two flakes... or maybe I just saw it in a movie once.
Anyway. The biggest problem with cold weather is the rate at which the different materials expand and contract. In this case you have somewhere between 3 and 5 different types of materials: glue, plastic, paint, metal and finecast. The good news is that these are relatively small figures. Which means that their total contraction is going to be relatively minor. So, I wouldn't worry about it.
However, you might have minis simply fall apart due to issues with the glue.
CA is brittle and doesn't stand up to the hot/cold temperature changes very well. But that's not saying too much.
CA tends to not hold up just over time within a controlled environment anyway.
If you used a liquid cement on the plastics, they should be just fine.
I guess I'd be more worried about getting frostbite if I decided to pull them out of the attic...
Chris.