Millions of Americans are gearing up to head to the airport or hit the highway for the first long weekend of the summer.

Thunderstorms that could pack high winds, large hail, flash flooding and a few tornadoes will extend from parts of Texas through Nebraska.

Americans are set to experience sharply different weather conditions across the country on Memorial Day weekend, according to forecasters at AccuWeather. While the Southwest is expected to experience heat, much of the eastern and central United States will contend with cooler temperatures, rain, and even thunderstorms.

SIOUX CITY (KTIV) - Thursday was a bit warmer with highs in the upper 50s and low 60s. While we saw some sunshine in Siouxland, there was a preponderance of cloud cover at times. More clouds roll in with rain that will stick around for the holiday weekend.

The weather data shows slight tweakings to the expected weather this weekend. The weather scene is still somewhat dismal for Saturday, but Sunday and Memorial Day are looking a little better.

Temperatures were expected to hover around 100 degrees through the Memorial Day weekend, with no chance of rain in the forecast.

“While some travelers embark on dream vacations and fly hundreds of miles across the country, many families just pack up the car and drive to the beach or take a road trip to visit friends,” said Stacey Barber, vice president of AAA Travel. Worst time: 1 p.m. to 9 p.m.

Long Island's weather has gone from summerlike back to spring, and forecasters say the cooler temperatures and rain are in store all week and into the holiday weekend. The National Weather Service says Memorial Day weekend, with the opening of summer beach season, could be hampered by cool temperatures and rain.