How are the numbers still visible on the football field in Philadelphia?

It is snowing like crazy in Philly. Big, huge fat flakes. You can hardly see the field. They’re playing in snow drifts. I can see where they’ve brush the snow away from the lines, maybe with a blower or something, but the numbers are still perfectly visible. They don’t look at all like they’ve been cleared. You can just see them. How is that?