I haven't ridden outside since Thanksgiving (and before that since the first weekend in October) and I'm totally fine with that. I don't need to suffer in the cold.

A long time ago I went on a ride with a good friend of mine - we started training/racing together in high school (and that's a long, long time ago, kind of like Fred Flintsone days). He told me during/after the ride that there are about ten days a year (here in CT) where it's just plain stupid to be riding outside, and we'd just ridden outside on one of those days.

Even if you're riding with a group it'll be sparse. I went to a Gimbles when it was 20 and blowing so strong our bikes got blown away from the car - we turned around after 5-10 minutes. There were about 20 people on the ride, it was so cold, so windy, it was just stupid. (And I relayed the 10 days a year story to the guy I drove with while we headed back to CT).

If you're riding with a really good friend/teammate/etc then it may be worth it (it's better than sitting next to each other on trainers). If riding alone I'd stay indoors.