As long as I've been on my team, we haven't had a real school closing in NYC. There was the subway strike last year, but that technically wasn't a school closure, and even if it was, it wasn't during the robotics season.
However, we always have finals week without classes during robotics season, and half of the week after that, most students aren't allowed to come to school. Come to think of it, all of the really big snow storms have been on days when we wouldn't have had school anyway. During finals week, we have meetings every day, and I think we're the only students in the school in the half-week afterwards.
It might be because of NYC's excellent public transit system, but we come to our school no matter what. Even on during the most awful snow storms, we come to work on the robot (when it snows, we all wear Hawaiian shirts
). That way, afterwards, we can have ourselves a good snowball fight, as we try to figure out how we're getting home.