Hundreds of millions of Americans spent Wednesday seeking relief from some of the coldest weather ever recorded in the continental United States.
Officials said temperatures were below the freezing mark in 85 percent of the country, excluding Alaska and Hawaii.
Chicago recorded a low temperature of about minus 23 degrees Fahrenheit (minus 30 Celsius) — not a record, but close to it. Minneapolis recorded minus 27 F (minus 32 C). In Sioux Falls, S.D., the mercury dropped to minus 25 F (minus 31 C).
Wind chills reportedly made it feel like minus 50 F (minus 45 C) or worse in several parts of the Midwest.
Downtown Chicago streets were largely deserted after most offices told employees to stay home. Trains and buses operated with few passengers; engineers set fires along tracks to keep commuter trains moving. The hardiest commuters ventured out only after covering nearly every square inch of flesh to protect against the extreme chill, which froze ice crystals on eyelashes and eyebrows in minutes.
The city used transit buses, with nurses on board, as emergency warming centers for the homeless.
Doctors in Minneapolis said they were treating cases of what they called fourth-degree frostbite, in which limbs are frostbitten down to the bone.
Mail carriers, known for making deliveries through rain, sleet and snow, draw the line at life-threatening cold. The U.S. Postal Service canceled mail service in parts of 11 states Wednesday.
With nine weather-related deaths reported so far, the cold was spreading east into New England and the mid-Atlantic states. Commuters and schoolchildren could expect to wake up to temperatures in the single or low double digits Fahrenheit in Washington, Baltimore, New York and Boston.
Meteorologists blamed the weather on a breakup of the polar vortex — cold air above the North Pole that has been pushed south across North America because of a blast of desert heat from North Africa.
Experts said it was possible that climate change was playing a part in the extreme cold. But they said it was hard to pinpoint the cause of a single weather event such as this week's cold blast.
"It is not out of bounds with the historical record," University of Miami professor Ben Kirtman said. "You get storms that are bigger than other storms. There is a big part of this that is part of the natural variability of the climate."
WATCH: Polar Vortex Sends Frigid Air Through North America
Government scientists said increased moisture in the atmosphere because of global warming might bring on a higher number of severe snowstorms in the winter and more powerful hurricanes in the summer.
This week's cold weather will be just a memory within a few days. Forecasters predicted temperatures in the mid-40s F on Sunday and low 50s F on Monday in Chicago. In Washington, the temperatures are expected to be in the mid- to upper 50s for those two days.
Some information for this report from the Associated Press.