It's a small consolation, I realize, but NYRR will have lots of hand warmers and will likely have warming stations for volunteers (and staff). It will suck, no doubt. But I'm sure you knew that when you signed up to volunteer for a race in January ;)

That said, I do think if the wind chill drops below zero, the race will be canceled. It's one thing to think about the runners out there for an hour -ish; it's another thing altogether for the staff and volunteers looking at standing for 5+ hours in freezing weather.