The plan is to smoke 2 turkeys tomorrow morning. I will be getting up at 5am to start "Reefer Madness" and run it up to 325°. The forecast is lower 20s with a 10mph wind and snow....1 to 2 inches. These exact conditions are the reason I built an automated, insulated pellet burner. As Ron Popeil says: "Set it and forget it".
Anyways, I would suggest everything the other guys are saying, create a wind block to minimize heat losses. Also, depending on your type of pit, insulate it somehow. I have a Chargrill Pro w/SFB. I threw blankets over the cook chamber and was able to BBQ in low ambient temps. I smoked 4 butts last year for the fire dept in January (I'm in Wisconsin.............yeah, effing cold!). Stiff wind and lower teens for temps. I used a "L" shaped wind block made from 4x8 sheets of plywood to shield the pit from the brisk wind and blankets over the cook chamber and I did OK. Lots of charcoal was used that night.............and I was up every 2 hours to reload with pre-lit charcoal. Those days are gone, thank God, now that I have the reefer.
Good luck!