CHICAGO >> A winter weather system expected to dump more than a foot of snow in some places has begun its trek east, with a separate blast of arctic air right on its heels.

Here are some things to know about this latest round of weather and its expected impact:

SNOWY COMMUTE

A storm that buried parts of the upper Plains and Midwest in snow, including 6 inches overnight in parts of central Illinois, wasn’t sparing states as it crawled across the Ohio Valley and Northeast, according to National Weather Service. Some locations will be hit hard, including by lake-effect snow, and could see accumulations up to 15 inches.

Washington, D.C., was hit by an unexpected 4 inches of snow early Tuesday after forecasts called for only an inch. Mayor Muriel Bowser said the morning commute was rougher than anticipated because of the weather, which also prompted numerous flight cancellations at Reagan National Airport, but that she expects the traffic to smooth out by the afternoon commute.

The system also brought snow to New Jersey, Pennsylvania and other eastern states on Tuesday.

COLDER TEMPERATURES COMING

Up next, the cold. A high-pressure system over Canada is expected to move toward the Plains on Wednesday and then slide east, bringing unusually frigid temperatures to the eastern two-thirds of the U.S., meteorologist Jamie Enderlen said.

Parts of Georgia could see low temperatures Wednesday in the teens, and northern Florida is expected to be at or below freezing. From the Dakotas across the Midwest and into the Ohio Valley, temperatures are likely to be below zero.

Come Thursday, New York City will “will be lucky if it hits 20” with lows near 10 degrees, according to Michael Musher with the Weather Service’s Weather Prediction Center.

Officials in the coldest areas are urging residents to bundle up to guard against hypothermia and exercise caution while driving. In Detroit and across Illinois, warming centers have opened to provide temporary relief from the cold.

TRAVEL TROUBLES LIKELY

The Weather Service warns that snow-covered roads and reduced visibility will create poor travel conditions in many areas Tuesday. Even after most snowfall has ended, increasing winds Tuesday could result in drifting snow.

At Chicago’s O’Hare International Airport on Monday night, airlines were reporting delays of 30 minutes for incoming and outbound flights and had canceled more than 230 flights, according to the city’s Aviation Department. At Midway International Airport, about three dozen flights were delayed.

In South Dakota, road conditions “are going to be deteriorating very rapidly,” said Mike Gillispie, a weather service meteorologist in Sioux Falls.

“If you don’t have to be out and about, it’s a good time to stay indoors,” he said.

RELIEF IS IN SIGHT

Temperatures are expected to be lower than normal for days but could rise a bit by the end of the week.

“We have cold temperatures, but it’s not like it never happened before,” said Bob Oravec, a meteorologist with the Weather Prediction Center. “It’s typical for an Arctic outbreak.”

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Associated Press writers Sarah Rankin in Chicago, Blake Nicholson in Bismarck, North Dakota, and Ben Nuckols in Washington, D.C., contributed to this report.