Back in the 1970s, Gary Siegwarth stuck a carton of ice cream in a snowdrift. “I thought it was the perfect hiding place from my siblings,” Gary told me, “Turns out the ice cream cache quickly metamorphosized into a subnivean shake… Gary had discovered the Subnivean Zone. This week, I’ve tucked thermometers into the snow in a less sticky way of observing the same magical phenomenon.