Any idea's on keeping the brood warm during a cold snap. My 2 hives are about 90% drawn out in first brood box. I'm ready to add second deep but I'll wait for a warmer, sunnier day before opening the hives. The hives are in a open field. I built a windbreak fence on the north and west side of hives. My wife suggested to stack a couple of hay bales to keep them warm.