Residents of the U.S. East Coast shivered on Thursday in blustery, frigid weather brought by a swirling cold air pattern called a polar vortex that earlier swept across the Midwest, with New England states facing wind-chill advisories.
The arctic air, which has Boston facing possible record-low temperatures on Friday, began blowing south from Canada into the Midwest earlier in the week, prompting authorities to warn of the risk of frostbite and hypothermia.
Two years ago, a southward shift in the polar vortex brought the Midwest some of its coldest weather in two decades.
The chilly air spread to the East Coast on Thursday, with the National Weather Service forecasting temperatures in New York City around 25 degrees Fahrenheit (minus-4 degrees Celsius) and similar cold in other cities including Philadelphia, Washington and Boston.
Wind chill advisories and warnings were issued by the National Weather Service for much of Maine, Vermont, New Hampshire and New York state.
"The coldest of the arctic air is just now arriving onto the East Coast," meteorologist Patrick Burke of the Weather Prediction Center said in a telephone interview.
Temperatures might drop enough in Boston that on Friday it could approach a record low, Burke said. Other areas along the East Coast as far south as Norfolk, Virginia, will also be unusually cold.
Connecticut Governor Dannel Malloy said he would activate the state's severe cold weather protocol beginning on Thursday evening, directing state officials to work with shelters to bring in homeless people.
In Chicago on Thursday morning, residents faced temperatures in the single digits and a wind chill of minus-16 degrees Fahrenheit (minus-27 degrees Celsius), according to the National Weather Service.
"Chicago's cold goes beyond the physical level of coldness. It pinches your soul," Twitter user Ivan Korkes wrote.
Cold temperatures in the Midwest and Plains were expected to persist on Thursday, with areas of North Dakota, Minnesota, Ohio and Indiana under National Weather Service wind-chill advisories.
The heaviest snowfall in the nation on Thursday will be around the Great Lakes in Michigan where up to 10 inches (25 cm) of snow was expected, and in parts of the U.S. West where a storm is pushing inland from the Pacific Coast, Burke said.
The Sierra Nevada mountain range in California and the mountains around Yellowstone National Park in Wyoming could receive more than two feet (61 cm) of snow, Burke said.