Firefighter Killed as Flooding Wreaks Havoc in Texas, Oklahoma Firefighter swept away while attempting water rescue in Oklahoma.

 -- An Oklahoma firefighter was killed attempting a water rescue and about 350 homes were under water in a small Texas town as a large part of the central and southern Plains states remained under a flash flood watch throughout much of Sunday.

In Claremore, Oklahoma, about 30 miles northeast of Tulsa, firefighter Jason Farley died when he was swept away while attempting a water rescue, said Deputy Chief Matt Wilson of the Claremore Fire Department.

The storms also forced the evacuation of the Rocklahoma music festival in Pryor, about 50 miles west of Tulsa.

Three to six inches of rain fell in the Oklahoma City metro area, which has had the rainiest 40 days and 40 nights in that city's history as more than 20 inches have fallen.

The National Weather Service in Norman, Oklahoma, also reported that 70 flash flood warnings have been issued in that area so far this year. That is more than were inssured over the previous four years combined.

The National Weather Service said major flooding continued along the Blanco River near Wimberley, Texas, about 40 miles southwest of Austin and 63 miles northeast of San Antonio. Rescues were ongoing in the area, where more than 9 inches of rain was reported as the Blanco River rose 35 feet within a few hours Saturday.

After a brief break from any heavy rain Sunday night, more rain is forecast to develop throughout the day on Monday. A new round of flash flood watches have been issued across a majority of eastern Texas to account for the next round of heavy rain and are in effect throughout Monday.

To the east, a tornado watch remained in effect across much of the Mississippi River Valley from Louisiana to western Illinois throughout Sunday evening, and even into part of the overnight period in some locations.

The threat for severe weather will encompass a large swath of Texas and the southern part of Oklahoma yet again on Memorial Day with large hail, damaging winds, and an isolated tornado possible across the region.

Throughout the day on Monday, areas of heavy rain will once again develop and bring the threat for more flash flooding to an already extremely saturated region.

While the flash flood threat will be more isolated than over the past 48 hours in this area on Monday, another round of potentially dangerous weather will affect millions across a stretch of the country that can't seem to catch a break.

The Associated Press contributed to this report.