Storm advisories were in effect Monday across a large swath of the central and eastern United States, from Texas and Oklahoma up through Ohio and Virginia, as meteorologists warned of flash floods, large hail and possible tornadoes.

Some 16 million people were placed under an "enhanced risk of severe thunderstorms," according to the National Weather Service, with major cities such as Dallas, Oklahoma City, Tulsa and Arlington facing the largest threat of tornadoes and "large to potentially giant hail." More than 30 millions others, from Arizona to Pennsylvania, were under marginal and slight risk of intense storm conditions.

“The severe threat will peak afternoon/evening in the southern Plains with the greatest threat for the Ohio Valley vicinity being the evening/overnight period,” the Storm Prediction Center said.

Over the weekend, the storm dropped tennis ball-sized hail over parts of Illinois and flooded low-lying areas throughout the Midwest, according to AccuWeather.

Meantime, showers and thunderstorms were expected Monday over parts of the mid-Atlantic region, hitting mainly Maryland, Virginia and West Virginia, the weather service said. Several inches of rain could cause localized areas of flash flooding, with urban areas, roadways and small streams being most vulnerable.

The large system "will be quasi-stationary through Tuesday morning," causing the weather service to extend an enhanced risk of severe thunderstorms over parts of the Plains and Midwest regions. As the storm heads East, it will threaten parts of Tennessee up through Ohio and across the Appalachians. Severe weather could be felt as far south as Florida later this week.

Storm bringing snow, cold weather to Northeast this later this week

The large storm system making its way across the country is threatening the Midwest and Northeast with an "all-out winter storm," according to AccuWeather.

Beginning on Tuesday, snow is expected to drop across parts of Wisconsin and Illinois before conditions intensify, with several inches of snow expected in parts of Vermont, New Hampshire and Maine, AccuWeather said.

Powerful wind gusts may snarl traffic and disrupt travel across the Atlantic Coast, AccuWeather said, adding that the combination of snow and wind is expected to last through Friday.

Rain damages section of vital California highway, prompting closure

A section of Highway 1 in California remains closed due to a partial collapse of the road that occurred Saturday amid a storm that drenched a large area of Southern California in several inches of rain, according to the state's Department of Transportation.

The collapse was reported Saturday as heavy rain fell in the area. By noon on Sunday, Caltrans crews were able to lead drivers through a single lane in the area, around the damaged section. The agency said on X on Sunday evening the highway remained closed on the Big Sur Coast due to a slip out just south of the Rocky Creek Bridge.

Though it didn't qualify as an atmospheric river because it lacks a strong link to tropical moisture, the area of low pressure that moved through Southern California represented a powerful final charge from the rainy season before the full-fledged transition to spring and the state’s dry months.

Contributing: Jorge L. Ortiz and Gabe Hauari, USA TODAY