Some of you, especially those of you who grew up in South Carolina, will recognize the significance of this image instantly.
For those of you who don't, let me explain:
We'd get snow about once a year in SC, and it usually didn't stick around. A lucky schoolchild would get a single snow day every other year. And even with the snow days that they get, the main activity for the day would be wishing that there was enough snow to go sledding. The warm blacktop just didn't often allow the snow to stick, except in the higher altitudes in the county (where the buses simply couldn't safely go if there was ice).
So approximately every three or four years, there would be enough snow for sledding.