A local radio program says wind-chill tonight is expected to be around -15F (-25C). A woman who runs a homeless shelter in the city was on the show. She said they have about 600 beds, and were about 85 over capacity last night, with people sleeping in chairs and on corridor floors.
Starting at around -19F, frostbite sets in at 30 minutes. "Frostbite" is one of those words people throw around willy-nilly, like "the flu" or "a migraine", but most of us haven't experienced it. Not really. If you've ever genuinely had the flu or a migraine, you know that they're more than just a bad cold or headache. "Frostnip" is a precursor to frostbite, where the skin turns red and hurts (it feels like it's burning, ironically). Anyone who lives in Canada, the US upper-midwest, Russia, or the Baltic countries has probably experienced frostnip, maybe every year. I've gotten frostnip myself, but never genuine frostbite. Ears and digits are the canaries in the coal mine; if the burning sensation stops and they go numb, you're on the clock. For people with light skin, frostnip turns you pink or red, frostbite turns you white (or whiter, as the case may be). I don't know what the visible indicators are for people with darker skin.
Anecdotally, a friend of mine who grew up in New England did a year of study abroad in Russia, and she said that, by far, the coldest weather she'd ever experienced was on the Baltic Sea, on a ferry out of St. Petersburg. She doesn't know what the temp or wind-chill actually was, but she wasn't able to smoke a whole cigarette before fleeing indoors. So, however cold it gets tonight, I can probably still say "well, at least I'm not in [North Dakota/Ontario/Siberia]."
Wind-chill chart from the U.S. National Weather Service:
