A series of destructive storms across parts of the south and central United States could wash out Memorial Day plans and snarl millions of Americans’ return trek home.

As of Monday afternoon, hundreds of flights had been delayed in the United States, with dozens of others canceled, according to data on FlightAware.com. The Dallas-Fort Worth area, which has seen several rounds of thunderstorms and gusting winds over the weekend and into Monday, has been the most affected by those delays, the flight tracking site said.

Dallas-Fort Worth International Airport, American Airlines’ largest hub, said it was expecting to serve about 1.4 million travelers over the holiday. Over the weekend, lines of hundreds of people deep snaked around the airport’s terminals.

Delays also continued into Monday at Denver International Airport after thunderstorms caused a temporary ground stop Sunday. Officials said a Southwest Airlines flight originating from Tampa, Florida, that landed in Denver on Sunday night may have been struck by lightning; no injuries were immediately reported.

It was also the first Memorial Day and major holiday travel weekend since the requirement that passengers have either REAL IDs or passports for domestic flights went into effect this month.

The storms Sunday produced more than 180 severe weather reports, including six preliminary tornadoes in New Mexico and Texas. Extremely large hail, some up to 6 inches, was also reported near Afton, Texas, east of Lubbock.

Isolated severe weather threats are expected to continue from Texas through the Deep South and parts of Florida into Tuesday, according to forecasts.

Through Memorial Day, a severe thunderstorm watch was in effect for parts of Louisiana and Mississippi. Eleven million people were at risk for damaging winds and large hail across parts of Texas, including Abilene, Austin and San Antonio; Louisiana; and Alabama. There’s also a continued chance of isolated tornadoes.

In addition, 12 million people remain under flood threats across the South into Tuesday morning, with the alerts stretching across the Texas, Arkansas and Louisiana regions.

NBC affiliate WESH reported that the potential for pop-up storms Monday across Florida, a popular holiday destination, could lead to ground stops late in the day at Orlando International Airport.

Officials said about a million people were expected to pass through the airport over the weekend, and the high volume could potentially lead to delays.

AAA expects a record 45.1 million people to travel at least 50 miles from home over the long holiday weekend. But most people — an estimated 38 million people, according to the association — are doing so by car.

And they’re benefiting from gas averaging $3.18 per gallon — the lowest Memorial Day price in more than four years, AAA reported.

For the majority of the United States, outdoor cookouts and travel plans home should remain on track.

Seasonal temperatures were anticipated across the Northeast with sun and clouds, while conditions were dry in the western third of the country.

HOUSTON – Rounds of severe weather barreled across communities from the Plains to the Southeast on Monday, slowing travel back home after the busy Memorial Day holiday weekend.

The powerful storms in Texas reportedly produced baseball-sized hail in some areas while hurricane-force wind gusts snapped trees like twigs, damaged property and knocked out power to hundreds of thousands of utility customers.

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In Harris County, a tree fell onto a home, causing significant damage after storms swept over the area.

As of Tuesday morning, FindEnergy.com reported more than 200,000 power outages in the Lone Star State, but those numbers were slowly dropping as crews worked to make repairs and restore electricity to those who were plunged into darkness.

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A dramatic video recorded in Austin on Monday night showed torrential rain falling as lightning illuminated the sky and wind roared as a severe thunderstorm moved over the area.

Another video showed more vivid lightning and loud thunder as a storm moved over the Marble Falls area.

SEE IT: FATHER-SON STORM-CHASING DUO CAPTURE PAIR OF TORNADOES IN TEXAS FIELD

NOAA’s Storm Prediction Center (SPC) received numerous reports of large hail falling across Texas on Monday.

Hail the size of a hen egg was reported near Saint Lawrence, while 3.5-inch hail, which is as large as a baseball, was reported in Menard.

Also in Menard, the SPC received a report of 5-inch hail, which is larger than a grapefruit.

GRAPEFRUIT-SIZED HAIL PELTS TEXAS AS MEMORIAL DAY WEEKEND STORMS BLAST SOUTH

The SPC said a trained spotter also saw a tornado to the southwest of Menard at the time, and there were numerous reports of funnel clouds across the area.

Wind also caused damage in Texas, and the SPC received a report of an 80-mph wind gust, which is as strong as a Category 1 hurricane, near Holland.

Thursday’s nor’easter is expected to bring heavy rain, strong winds and possible coastal flooding to New England.

Here’s a closer look at the timing and potential impacts, by region:

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Timing:

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An incoming nor’easter is raising travel concern as AAA predicts over 1 million drivers will be on the road during the holiday weekend in Massachusetts.

Wind gusts forecast:

Total rainfall numbers:

Impacts, by region: