A blast of Arctic air will plunge temperatures across the eastern United States this week — and the frigid conditions could last longer, exposing millions of people to prolonged and dangerous winter weather.

“We’re going to be stuck in a cooler trend,” said Zachary Yack, a Chicago-based meteorologist with the National Weather Service. “It will definitely start in the middle and beginning of next week.”

The Arctic outbreak has already caused temperatures to plummet in the northern Plains states. Forecasters predicted the high temperature in Minneapolis would be 20 degrees on Thursday and drop to 12 degrees on Saturday.

Temperatures in Chicago next week are expected to be in the low 20s. Forecasters in both cities expect overnight temperatures to drop into the single digits.

Yack said a low pressure system is moving south, dragging arctic air from northern Canada.

Distortions in the jet stream — patterns of strong winds in the upper atmosphere — will cause cold air to stagnate and linger over much of the eastern United States.

“The jet stream will be concentrated in the central and southern portions of the United States. There’s nothing that can move it back,” Yack said.

Temperatures are expected to remain well below average – even in January.

The system will not be limited to the Midwest and Plains states.

“The coldest air of the season so far and dangerous wind chills are likely across many areas of the Southeast,” the National Oceanic and Atmospheric Administration’s Climate Prediction Center wrote in a long-range forecast. “Below freezing temperatures are possible up to the Gulf Coast and much of the Florida Peninsula. Impacts on highly sensitive citrus fruits are possible.”

Snow is possible in the southern Plains states and the Southeast, with heavy snow possible in the Appalachian Mountains, Ohio Valley, Great Lakes and interior Northeast.

The Climate Prediction Center’s forecast eight to 14 days ahead predicts below-average temperatures for nearly all of the eastern United States, suggesting the system could persist beyond next week.

Yack said he is concerned about Chicagoans who work outside and vulnerable populations, such as those experiencing homelessness.

“You could have wind chills below zero. This could lead to frostbite in short periods of time,” he said.