There hasn’t been much snow this winter but last month, on the day following one small snowfall, I noticed a few “positive” footprints on the sidewalk. Positive seems to me as good a way as any to describe footprint shaped patches of snow on an otherwise clear sidewalk. I unfortunately didn’t have my camera but have seen the likes of this before, although not very often.
I think what happens is that the temperature is just cold enough for snow, in this case around two inches. Someone walks on it and compresses it which lowers its temperature and freezes it. So the snow that has the footprint shape is now ice surrounded by wet sluggish snow which slowly melts because it’s just warm enough. The ice prints melt too, but not as fast.
Last Sunday while I was walking out in the country side, at a higher altitude so there were still patches of snow here and there, I found this small snow circle that was similarly made by the pole of a cross country skier. And I did have my camera!