Ok so I did a brisket cook last night and had it today for xmas eve. So I started at 9pm and it was already very cold. It was about 15 degrees overnight. I got up at 8am to check it was good but at 9 it started going down very quickly. I used weber charcoal. My last cook was great and the coals lasted over 20 hours. I used a little less charcoal this time so I could fit the wood in it. So the temp was at 156 and I slept for another hour and the temp went down to 151 and it was dropping quickly. This is the first cook I have done in weather this cold that required more than 5 hours of cooking. So I am thinking that when the temps are that low then I need to take the whole base and top off and replenish the coals that way after say maybe 10 hours or so in the colder temps. It also started snowing pretty heavily early am so I am sure that didn't help. I hope my atc didn't break. Does anyone have any thoughts on how to keep temperature up in the extreme cold?