We're getting a polar vortex that is bringing the coldest temperatures we've had in decades here in Pennsylvania. I'm headed to the mountains to construct a snow shelter, which is where I'll sleep during the coldest night of the year. I'm also testing my new North Face Inferno -40° sleeping bag to see how it performs. The lowest temperature I observed on my thermometer was -18°F. It stayed around 25 to 30 degrees warmer in my shelter than it was outside