Don’t forget to check your local weather forecast before you head out: Snowfall could disrupt post-Thanksgiving travel plans in the northern Plains and Midwest, while around 9 million people in the South are under freeze warnings.

In the Great Lakes region, a heavy lake-effect snow event is expected to continue through the weekend before tapering off early next week. Six million people were under winter alert Friday from northern Minnesota to New York state, where snow totals downwind of Lakes Erie and Ontario were expected to reach 3 feet or more.

An arctic air mass is bringing the coldest air since last winter to the Plains and Midwest, as well as the South and East Coasts, according to the National Weather Service. It is forecast to extend through the weekend and into the week.

The northern Plains and upper Midwest will experience subzero wind chills Saturday morning, and parts of North Dakota could see wind chills of minus 30 to 40 degrees, the weather service said.

New York Gov. Kathy Hochul declared a state of emergency on Friday, which went into effect immediately in Allegany, Erie, Cattaraugaus, Chautauqua, Genessee, Herkimer, Jefferson, Lewis, Oswego, St. Lawrence and Wyoming counties.

Snowfall rates will be tremendous at 3 to 4 inches per hour and may be accompanied by thunderstorms, a rare weather event that combines a blizzard with thunder and lightning. The highest snow accumulations will occur east of Lake Ontario, where some isolated areas around Watertown, New York could see up to 60 inches of snow.

Traffic could be particularly difficult on Interstate 90 between Cleveland and Buffalo. The interstate in Pennsylvania was closed late Friday afternoon between Interstate 79 and the New York state line, Erie County Executive Mark Poloncarz of New York said during a news conference.

Other roads that may be affected include Interstate 81 north of Syracuse, New York. The “Sunday Night Football” matchup between the San Francisco 49ers and the Buffalo Bills could be buried under snow as Highmark Stadium is located in Orchard Park, a city where the snowpack is expected to reach between 12 and 18 inches, with higher amounts are possible.

The Buffalo Bills signed up for their die-hard fans, dubbed the “Bills Mafia,” to shovel snow at the stadium on Friday on X.

Poloncarz said during the media briefing that central and southern Erie County will most likely be the hardest hit with the bulk of the snowfall arriving Saturday and Sunday. The central regions of the county could see between 2 and 3 feet of snow, while the southern part of the county could see more than 3 feet of snow, Poloncarz said.

Police said wintry weather was likely the cause of a crash on U.S. Route 131 in Grand Rapids, Michigan, Thursday evening that left people injured. Authorities did not provide a specific number of people injured in the incident. The collision reportedly involved up to 15 vehicles, police said.

U.S. airports were crowded with travelers heading to Thanksgiving destinations between Sunday and Thursday. The Federal Aviation Administration transported more than 232,000 flights safely across the country between those days – a record number for Thanksgiving week. On Tuesday alone, more than 52,000 flights transported passengers to their destinations.

Meanwhile, about 9 million people were under freeze protections and warnings Friday across the South, from Texas to the Carolinas.

Weather forecasters say the coldest air is yet to come to the south and an arctic air mass is moving south from Canada.