Heavier than expected snow snarled traffic in Washington on Tuesday, forcing Attorney General Eric Holder to cancel a trip to New York for the funeral of former Governor Mario Cuomo, while the U.S. Midwest prepared for brutal cold.

The Washington region got up to 5 inches of snow, well above initial forecasts. Hundreds of car crashes were reported in the morning commute and some area schools closed. Dozens of flights were delayed or canceled at local airports.

In the Midwest, residents were bracing for another round of harsh winter conditions.

Temperatures there could plunge to 25 to 30 degrees below average on Wednesday, forecast to be the coldest day of the week, a National Weather Service forecaster said.

Chicago Public Schools, the country's third largest district, canceled classes on Wednesday, saying weather conditions were too dangerous for children to travel to school. Minneapolis public school classes were also canceled on Wednesday. Many schools in central and southern Ohio were closed on Tuesday.

Chicago-area commuter rail service Metra planned to take extra precautions on Tuesday evening, including running train engines overnight and having staff on hand to oversee key switches.

"These are things we do when we have extreme winter weather," Metra spokesman Michael Gillis said.

Overnight, temperatures in the Dakotas and Upper Midwest could drop as low as minus 15 or 20, with highs on Wednesday remaining below zero.

Law enforcement agencies in Iowa and the Dakotas alerted residents to prepare for bitter cold.

The administrator of a dialysis clinic in Sioux Falls, South Dakota, pledged to keep the unit open unless there was a severe blizzard.

"We tell our patients if they're traveling, to pack a bag, have medications for three days, have blankets and let people know when they are coming and going to their appointment," said Donna Osment of the DaVita dialysis unit.

On the East Coast, the coldest day of the week will be Thursday, National Weather Service forecaster Bob Oravec said.

There will be lake-effect snow showers across the Great Lakes region, hitting parts of Michigan, Ohio, New York, Pennsylvania and Indiana, Oravec said. Over the next three days, the heaviest snow will fall across western and northern New York and northwest Pennsylvania, which could see more than 2 feet of snow.

A foot or more could fall in Michigan's Upper Peninsula and in northeast Ohio, Oravec said.