I have never run a nitro below 40 degrees F, but in the past when I ran in the 40-45 degree range I would put a sock or rubber band some paper to the heatsink head to block airflow in order to get the temps up.
Don't expect to run the engine at the same temps as a warm day. For example, when I was running at 40 F, the engine was running at about 200 F. Also, when it's cold, you run richer not leaner.
Olds97 should chime in about the snow as I've seen him post pics of his Savage with icicles on it.