Infected with squirrel pox virus. This was one of three individuals afflicted in a group of about 10 individuals, this one the worst case. It was foraging on the ground a bit away from the others reasonably okay, but was clearly hobbled by the sores.
I watched this squirrel bring some leaves into the tree cavity of this Black cherry, for some insulation. Here is the squirrel after emerging again.
Licking the... snow?
Footage: https://youtu.be/olzjj1dFPjw