MILWAUKEE (Reuters) – A major winter storm was expected to clobber a large swath of the northern United States with heavy snow, gusty winds and frigid temperatures making travel difficult and dangerous starting on Friday and through the weekend, forecasters said.

The storm system will dump 6 to 10 inches (15 to 25 cm) of snow in the Plains and Midwest on Friday night and Saturday and as it moves east at least a foot of snow in parts of the Northeast on Saturday and Sunday, the National Weather Service (NWS) said in several advisories.

The system was expected to also bring freezing rain, wind gusts of 35 miles (56 km) per hour and quickly dropping temperatures that will to dip into the teens and even below zero Fahrenheit in several areas, the service said.

“If you don’t have to go outside, it probably is best that you don’t,” said Amy Seeley, an NWS meteorologist in Chicago. “People will have to worry about blowing and drifting snow.”

Forecasters and officials in several states warned that snow accumulation and drifts on highways and roadways will make driving difficult and dangerous.

More than 900 domestic flights had been canceled and another 3,100 delayed as of 4 p.m. EST (2100 GMT) on Friday, according to Flightaware.com, an online tracking service.

Several airlines said on Twitter they will issue waivers and told travelers to expect more delays and cancellations during the weekend.

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.

Pennsylvania Governor Tom Wolf declared a state of emergency for his state where he said two inches of snow per hour was expected. Speed limits on many Pennsylvania highways will be restricted to 45 mph, he said.