A major winter storm is delivering dangerous weather across the Upper Midwest, Great Lakes, and Northeast this weekend.

According to the National Weather Service (NWS), the storm system is expected to strengthen over the coming days, with hazardous conditions likely to last through Tuesday.

“Arctic air will spill into the Plains beginning Sunday, followed by a powerful winter storm moving from the Upper Midwest to the Great Lakes Sunday night into Monday,” the NWS said in a bulletin issued Saturday.

Heavy snowfall and near-blizzard conditions are expected in parts of the Upper Midwest and Great Lakes, creating “treacherous travel,” the agency warned. More than a foot of snow is possible across Michigan’s Upper Peninsula, while western New York and northwest Pennsylvania are forecast to see significant lake-effect snow.

The storm has already impacted the Northeast, dropping up to 8 inches of snow on New York City and surrounding areas from Friday into Saturday. The weather caused major slowdowns along the I-95 corridor and widespread flight disruptions. By Saturday evening, more than 1,000 delays were reported nationwide, and nearly 1,000 flights had been canceled into, out of, or within the United States, according to FlightAware.

The NWS is also cautioning residents in parts of the Northeast about dangerous icing, with as much as a quarter-inch of ice possible in eastern New York, as well as parts of Connecticut and Massachusetts. Wind chills could plunge to –35 degrees in portions of North Dakota and to –25 degrees in northern Minnesota.

In contrast, much warmer, almost springlike conditions are expected across parts of the South and the Tennessee Valley, where temperatures could climb into the 70s, forecasters said.