A weekend storm sent temperatures plunging well below zero in the Midwest and dumped heavy snow on parts of the Northeast on Sunday, creating many airport delays and slick roads as the Pacific Northwest braced for more rain after days of flooding and mudslides.

Approximately 63 million Americans are under a cold weather advisory, and around 11 million are under a freeze warning — mainly in the Gulf Coast states, where such low temperatures are rare.

The storm began Saturday and brought up to several inches of snow in the New York-New Jersey metro area, the region’s first significant snowfall of the season. Light snow fell over parts of New England. The storm was expected to weaken by Sunday night, followed by arctic conditions with overnight windchill temperatures at or plummeting below zero degrees (-18 Celsius).

As frigid air shifts from the Great Lakes into the East Coast, there will be dangerously low temperatures, according to forecasters. Some places could dip down to record levels.

Crews and contractors were out plowing and treating roads in New Jersey, where the state Department of Transportation advised people to avoid unnecessary travel. Salt spreaders and plows worked overnight to clear snow from roads and bike lanes, the New York City Department of Sanitation posted online. The state of Pennsylvania temporarily reduced speed limits on interstates to 45 mph (72 kph).

There were over 1,000 flights delayed and more than 100 cancellations at U.S. airports due to the weather, according the flight tracking site FlightAware.

Meanwhile, a blast of arctic air swept south from Canada and into parts of the northern U.S. The National Weather Service in Chanhassen, Minnesota, said Sunday was the coldest morning of the season so far. It was -10 degrees (-23 C) at Minneapolis-Saint Paul International Airport, with temperatures as low as -22 (-30 C) in some communities. In the Chicago area, wind chills of -20 to -25 were reported Sunday morning.

In the Pacific Northwest, which has seen catastrophic flooding that has forced thousands of people to evacuate, more rain and wind were expected in the region as early as late Sunday, forecasters said.