The blast of Arctic air that brought record-breaking cold, causing at least a dozen deaths and canceling or delaying thousands of flights in the U.S. Midwest, spread eastward on Thursday, bringing frigid misery to the Northeast.
A forecast for warmer weather by the weekend offered little comfort to those enduring icy conditions, brutal winds and temperatures as low as minus 30 degrees Fahrenheit (minus 34 Celsius).
"This morning is some of the coldest of the temperatures across the Upper Midwest, and we still have some dangerous wind chills," Andrew Orrison, a forecaster for the National Weather Service, said in a phone interview.
In Minnesota and Upper Michigan, temperatures will be at minus 20F (minus 29C) on Thursday and parts of North Dakota can expect minus 30F, forecasters warned.
The bitter cold was caused by displacement of the polar vortex, a stream of air that normally spins around the stratosphere over the North Pole but whose current was disrupted. It pushed eastward and states including Massachusetts, New York and Pennsylvania experienced bitterly cold temperatures. The overnight low in Boston was at minus 5F (minus 21C), according to the National Weather Service.
"This morning is the worst of the worst in terms of the cold," Orrison said. "It'll be the coldest outbreak of Arctic air (so far this winter) for the Mid-Atlantic and the Northeast."
It has been more than 20 years since a similar Arctic blast covered a swath of the Midwest and Northeast, according to the weather service.
The cold has caused at least 12 deaths since Saturday across the Midwest, according to officials and news media reports. Some died in weather-related traffic accidents, others from apparent exposure to the elements.
Videos this week showed boiling water freezing as it was tossed in the air in Cedar Rapids, Iowa, and transit workers in Chicago setting fire to train tracks to keep them from locking up.
Even parts of the South, such as the mountains of Kentucky, Tennessee and upper Georgia, will be in the single digits, the weather service said.