Tips for running in cold weather?

I'm training for a 5K race on Thanksgiving Day. I ran one last June, without much of a problem. I'm still in pretty good shape, as far as leg stamina and weight and such, but my problem is my breathing. I have trouble breathing when I run in cold weather. The weather's in the 50s and will probably be in the 40's on Turkey Day, so can anyone offer any tips for running in cold weather? Thanks!