WASHINGTON — Chaotic weather, from surprising heat in California to the threat of storms rolling into the East Coast, put over half the U.S. population in the path of extreme conditions Monday.

Storms across the nation’s eastern half forced airlines to cancel roughly 4,000 flights nationwide Monday, and many schools closed early in the mid-Atlantic states, where high winds were in the forecast.

Blizzards buried parts of Michigan, Wisconsin and Minnesota while torrential rains flooded homes and washed out roads in Hawaii.

In Washington, the House and Senate postponed votes, and federal agencies told workers to go home early. But by late afternoon, the expected rough weather had failed to develop and a tornado watch expired.

Airport delays and cancellations piled up Monday in some of the nation’s largest airports — including those in New York, Chicago and Atlanta.

The private weather service AccuWeather calculated that more than 200 million people were under threat Monday of some kind of dangerous weather.

Those range from extreme heat and wildfire advisories to flood and freeze watches from the National Weather Service.

Forecasters warn about line of storms, tornadoes

The storm system that dropped snow by the foot in the Midwest barreled toward the East Coast with the potential for high winds and tornadoes, the weather service warned Monday.

“Wind is the primary threat, but within any of these areas of strong wind there could be some embedded tornadoes,” said Evan Bentley, a meteorologist with the weather service.

The biggest threat stretched from Maryland to the upper edge of South Carolina.

In New York City, four people, including a child, died Monday afternoon after a fire in a three-story apartment building spread during heavy winds.

Blizzard conditions continued in the Upper Midwest and Great Lakes on Monday after the storm walloped parts of Wisconsin and Michigan with several feet of snow.

Since Saturday, nearly 3 feet had fallen in the northern Wisconsin town of Mountain.

Another round of snow and gusts on Monday could bring another foot of snow across Michigan’s Upper Peninsula.

A heat dome over the Southwest will push temperatures well into the triple digits in Arizona most of the week, much earlier than normal.