(NewsNation) — Thunderstorms, flash flooding and possible tornadoes could impact millions in the central and Southern Plains this week.

The National Weather Service’s Storm Prediction Center estimates 28 million are at a severe weather risk Wednesday, while 37 million will be under one Thursday.

Tornadoes, along with very large hail and severe wind gusts, are likely in the Southern Plains, the National Weather Service tweeted Wednesday afternoon. The Storm Prediction Center said these storms are likely to be severe.

NewsNation meteorologist Gerard Jebaily said the risk for a tornado is particularly high in Oklahoma and Texas where the threat is rated a 4 of 5.

Portions of the southeast Texas panhandle, as well as southwest Oklahoma and north Texas, could experience a few strong tornadoes and giant hail, according to the Storm Prediction Center. The outlook for the area was upgraded to a moderate risk by the Storm Prediction Center Wednesday afternoon.

Some areas could see three to five inches of rainfall, with isolated higher amounts, the National Weather Service said.

Forecasters said the greatest severe weather danger will shift farther to the west Wednesday night, according to AccuWeather.

Similar severe weather is expected this weekend, with 12 million at risk for possible tornadoes, damaging winds with gusts up to 70 mph, and large, golf-ball-sized hail.

“Review your severe weather safety procedures for the possibility of dangerous weather today,” the National Weather Service said. “If a tornado warning is issued for your area, move to a place of safety, ideally in a basement or interior room on the lowest floor of a sturdy building.”