Severe weather stretching across the Midwest and East Coast on Monday disrupted plans for millions of Americans trying to make it home after a busy weekend that was expected to break records for Memorial Day travel. The disruptions followed storms and tornadoes that killed at least 23 people in the South and left hundreds of thousands without power.

Flights at airports from Atlanta to Boston experienced ground delays and stops as severe weather, including heavy rain and potentially damaging wind and hail, moved into much of the Eastern United States on Monday afternoon and evening.

Parts of New York, New Jersey and Pennsylvania were under severe storm watches through late Monday, and a tornado watch was issued for an area from northern Maryland through eastern North Carolina, including Washington, D.C. Heat and more thunderstorms were forecast for Texas and the Southern Plains on Tuesday, including possible hail and strong winds.

Officials with the Federal Aviation Administration said that they had worked with the airlines to plan for the expected weather disruptions over the Memorial Day weekend. On Friday, 2.9 million people were screened at U.S. airports, the Transportation Security Administration said — a single-day record.

By midday on Monday, La Guardia Airport in New York City had reported average ground delays of 100 minutes. Flights were also delayed at Hartsfield-Jackson Atlanta International Airport, the busiest in the world. And ground stops and major delays were reported or expected at airports in Chicago, Virginia, Baltimore, Washington, Philadelphia and Cleveland because of the storms, according to the F.A.A.

In Kentucky, Gov. Andy Beshear declared a state of emergency on Monday morning after four people were killed over the weekend. On Monday afternoon, Gov. Beshear announced a fifth storm-related death in the state, a person who died from a heart attack while cutting fallen trees. More than 150,000 customers in the state were without power at midday after damaging winds.

Elsewhere, a tornado left at least seven people dead in North Texas, including two children ages 2 and 5. Eight people were killed in Arkansas, and two died in Oklahoma as severe storms swept through the region, flattening hundreds of buildings and blowing away homes. And severe thunderstorms in Virginia resulted in at least one fatality, officials said.

Thousands of others in the South and the Midwest were without power on Monday, according to the tracking site poweroutage.us.

Later on Monday, severe thunderstorms were expected from Texas to New York, the National Weather Service’s Storm Prediction Center said. Flash flooding was possible from Maryland to the Catskill Mountains in New York, the Weather Service said, and tornadoes were possible in the Mid-Atlantic region.

The system was the latest to pummel the region over the past few days. Five people were killed and part of a city was obliterated in Iowa last week after a powerful tornado hit.

President Biden issued a statement of condolence to those affected by the storms, and he thanked emergency responders for their work.

“Jill and I are praying for those who tragically lost their lives as a result of devastating tornadoes that tore through Texas, Arkansas and Oklahoma, leveling entire communities and leaving a path of destruction in their wake,” Mr. Biden said.

Mr. Biden said that the federal government was “ready to provide support as needed.” He noted that the Memorial Day holiday storms came just weeks after counties in the Midwest and South were recovering from severe weather.

On Sunday, severe thunderstorms in Howell County, Mo., produced hail the size of baseballs and tornadoes that downed trees and damaged homes near the town of Mountain View, said Kelsey Angle, a meteorologist with the National Weather Service in Springfield.

In Kentucky, Governor Beshear deployed the National Guard to help state forestry workers clear downed trees and dangerous debris. He activated the state’s price-gouging statute to prevent price increases on necessary supplies, and said he believed that the state would qualify for public assistance from the Federal Emergency Management Agency.

Emergency workers have reported high water, fallen trees and other dangerous conditions in about a third of Kentucky’s 120 counties, mostly in the western part of the state, Jim Gray, the Kentucky transportation secretary, said at a news conference. The storms also impacted nearly 100 state highways.

In Texas, Governor Greg Abbott signed a severe weather disaster declaration that covered 106 counties. Officials estimate that nearly 100 people were injured over the weekend, more than 200 homes were destroyed and over 220 buildings were damaged.

Johnny Diaz and Mike Ives contributed reporting.