The blast of Arctic air that brought record-breaking cold and caused at least a dozen deaths in the US midwest has spread eastward, bringing sub-zero misery to the country's northeast.
A prediction of warmer weather by the weekend offered little comfort to those enduring icy conditions, brutal winds and temperatures as low as minus 34degC.
"This morning is some of the coldest of the temperatures across the upper midwest and we still have some dangerous wind chills," National Weather Service forecaster Andrew Orrison said on Thursday.
In Minnesota and upper Michigan, temperatures are forecast to be at minus 29degC on Thursday (US Time) and parts of North Dakota can expect minus 34degC, 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 were experiencing bitterly cold temperatures.
Boston was at minus 15degC, according to the National Weather Service.
"It'll be the coldest outbreak of Arctic air for the mid-Atlantic and the northeast," Mr Orrison said.
The cold has caused at least 12 deaths since Saturday across the midwest, according to officials and 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, Illinois, 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, are expected to be in the single digits.
More than 30 record lows were shattered across the midwest.
Some areas only saw a high of minus 23degC on Wednesday.
The lowest on Wednesday was minus 40degC in International Falls, Minnesota.
But the picture is set to change. By this weekend, Chicago, which had near-record cold of minus 30degC on Wednesday, will bask in snow-melting highs in the 7-11degC range. So will other parts of the midwest.
"It's going to feel quite balmy in comparison," Mr Orrison said.
More than 2500 flights were cancelled and more than 3500 delayed on Thursday morning, most of them out of Chicago's O'Hare International and Midway International airports, according to the flight tracking site FlightAware.com.