(The Hill) — More than 20 million people face a threat of severe thunderstorms, and some areas are bracing for tornadoes ahead of what could be the busiest holiday travel week ever.

According to the National Oceanic and Atmospheric Administration’s (NOAA) Storm Prediction Center, there are expected to be some strong tornadoes and “damaging thunderstorm winds” and large hail in parts of east Texas and Louisiana.

Experts said the storm will move then into the Delta region and parts of Mississippi and Alabama. The storm is expected to move northeast and spread rain in Washington, D.C., Maryland and Virginia by Tuesday morning, with snow farther north.

Parts of eastern Texas, northern Louisiana and central Mississippi have been issued between a level 3 and 5 storm risk level. Some areas could see tornado speeds of 111 mph or more.

Residents who live in Shreveport, Monroe and Bossier City, La., and Jackson and Hattiesburg, Miss., are in the areas that NOAA classified as “enhanced risk.”

The storm may bring relief to areas that have been drought-stricken through its expected “excessive rainfall.”

The storm is striking the country during one of the busiest holiday travel weeks of the year. The Transportation Security Administration (TSA) said airlines are preparing for what is expected to be the busiest holiday travel season.

More than 30 million people are expected to travel by air during a period that began last Friday and goes until the Sunday after Thanksgiving.