US air traffic snarled

Airlines canceled 1,500 US flights during the peak holiday travel period Friday, with severe winter storm warnings and heavy snow forecast across parts of the Midwest and northeast.

More than 40 million Americans were under winter storm warnings or weather advisories one day after Christmas, plus another 30 million under flood or storm advisories in California, where a so-called atmospheric river has brought a deluge of rain.

New York, the country's largest city, was bracing for up to 10 inches (25 centimeters) of snow overnight — the most in four years.

Temperatures were forecast to drop and remain chilly into the weekend, when an Arctic blast swoops down from Canada.

At least 1,490 flights had been canceled, with more than 5,900 delays, as of 4:00 pm US Eastern time (2100 GMT) Friday, the FlightAware website said.

The National Weather Service (NWS) predicted snowfall across the upper Great Lakes region would move towards the US northeast.

"Difficult travel conditions are ongoing for the area and those traveling from the holiday should exercise caution if you have to be on the road," it warned.

New York Mayor Eric Adams said a winter storm warning was in effect, and that city crews were deployed to plow roads.

Airports in New York and Chicago were near the top of FlightAware's rankings on its "Misery Map," which tracks the spread of flight delays and cancelations.