I don't know.

Pity me; I come from a warm country where we rarely have the kuxury of snow between say, October and March...

And not a great deal more between March and October either...

Still, my spies inform me that even in more blessed climes the snow sometimes melts, forming water, whiich drains down past the rims of manhole covers, carrying residual ice particles floating in it, and that those particles get sieved out  at the edges of the covers, forming piles of ice that congeal to form impromptu sleeping policemen.

And beware of mocking my spies!  They know who you are and where you live....