(Reuters) – A winter storm that has blanketed the U.S. Midwest with snow advanced on the U.S. Northeast on Saturday, forcing the cancellation of flights and train service during a holiday weekend when many Americans were traveling.

The Weather Service has issued winter storm warnings or advisories for a swath of the eastern United States that is home to 100 million people, said meteorologist Rich Otto of the U.S. Weather Prediction Center.

The storm system, which was moving from west to east and was strengthened by arctic air from Canada, hit many parts of the Midwest on Friday, according to the National Weather Service.

In Chicago, where some neighborhoods received 8 inches (20 cm) of snow, one third of flights were canceled at the city’s two main airports, said Mark Duell, vice president of operations for tracking firm FlightAware.

The storm was expected to dump up to 2 feet (60 cm) of snow on the Northeast starting on Saturday evening, with snowfall likely to last until Monday in upstate New York and Maine, Otto said.

New York City was expected to receive up to 2 inches (5 cm) of snow.

Gusty winds will bring the coldest air parts of the U.S. East Coast have seen all winter, according to the National Weather Service. For instance, the temperature in Boston could drop to 6 degrees Fahrenheit (-14 degrees Celsius) on Sunday.

The governors of New Jersey and Pennsylvania declared emergencies for their states ahead of the storm, warning of high snow accumulation and even potential flooding in some areas.

The storm was sweeping across the eastern United States ahead of the Martin Luther King Jr. Day on Monday, a holiday honoring the late civil rights leader.

The U.S. Transportation Security Administration had said it expected the long weekend to be a busy one for travel.

The storm has interrupted some travelers’ plans.

From Friday through Sunday, the severe weather was expected to trigger the cancellation of more than 3,000 flights in the United States, Duell said.

Meanwhile, in some parts of the Northeast, the Weather Service warned snow-covered roads could leave some people stranded on Saturday night and Sunday.

“If you don’t have to be on the roads, we recommend staying in and staying safe,” Automobile Association of America spokeswoman Jeanette Casselano said in a phone interview.

Amtrak canceled train service from Chicago to Boston, Washington, D.C., and New York on Saturday and canceled and modified several routes that originate and end on the East Coast on Sunday.