Don’t forget to check local forecasts before hitting the road or check out Black Friday deals: Snowfall could disrupt post-Thanksgiving travel plans in the Northern Plains and Midwest, while an estimated 9 million of people are under freezing surveillance in the South.

In the Great Lakes region, a vigorous Lake effect snow event is expected to last through the weekend before easing early next week. Six million people were under winter alert Friday, from northern Minnesota to upstate New York, where snowfall totals downwind of Lakes Erie and Ontario were expected to reach 3 feet or more.

At times the snowfall will be blinding, 3 to 4 inches per hour, and could be accompanied by thunderstorms, a rare weather event that combines a snowstorm with thunder and lightning. The heaviest snow accumulations will be east of Lake Ontario, where some isolated areas could see up to 60 inches of snow around the Watertown, New York area.

Road travel may be particularly difficult on Interstate 90 between Cleveland and Buffalo and on Interstate 81 north of Syracuse, New York. The Sunday night showdown between the San Francisco 49ers and Buffalo Bills could be buried in snow because Highmark Stadium is in Orchard Park, a town expected to pick up between 12 and 18 inches, with higher amounts possible.

Meanwhile, some 9 million people were under frost watches and warnings Friday across the South, from Texas to the Carolinas. Cities under alert include Abilene, Texas; Shreveport, Louisiana; Jackson, Mississippi; and Charleston, South Carolina.

Meteorologists expect the coldest southern air to come, with an Arctic air mass spilling south out of Canada.