Ice Fog

I enjoyed a lovely walk this morning with the dogs, with temperatures bottoming out at -45F below. Without booties, the dogs pathetically limp around, trying to figure out how to take care of business without actually touching all four paws to the ground. At these temperatures, Fairbanks experiences intense ice fog:

http://climate.gi.alaska.edu/

Ned Rozell, a local science writer, describes the origin of ice fog:

Ice fog is what happens when water vapor meets bitter cold air that can't hold any more water. When water vapor exits a car tailpipe when it's minus 40, for example, the water vapor temperature drops from about 250 degrees to minus 40 in less than 10 seconds. Water cooled that fast forms tiny ice particles, so small that ten of them could fit side by side on the finger-cutting edge of a piece of paper. Collectively, millions of these particles take form as ice fog, the cotton candy-like clouds that hang over our roads.

Temperature inversions, in which warm air above acts like a lid to trap cold air below, combine with hills in Fairbanks to provide a box in which ice fog forms. Inversions usually allow hilltop residents to bask in warmer temperatures than those living in low areas, but ice fog often takes away the advantage of living in the hills. Inversions usually form at the ground surface in Fairbanks, but during bouts of ice fog, inversions form at the top of the ice fog layer. The warmer air usually enjoyed by those at higher elevations forms higher in the atmosphere; those in the hills experience the same numbing temperatures as the lowlanders.