CNN
 — 

A strong storm on Friday brings the threat of torrential rain across a large swath of the US stretching from Oklahoma to West Virginia while some areas in the South may see tornadoes, hail potentially damaging winds.

More than 20 million people are under flood watches across at least eight states in the mid-South and central regions.

“A dangerous, flash-flooding and severe weather event is expected tomorrow (Friday), as heavy rainfall focuses along a slow-moving cold front across the Ohio Valley, while tornadoes, damaging winds, and hail develop south of the boundary in the Lower MS Valley and Mid-South,” the Weather Prediction Center warned Thursday afternoon.

The storm’s worst impacts were over the Oklahoma-Missouri border late Thursday, drenching parts of the states with 1 to 3 inches of rain in areas where a flash flood warnings is in effect. Those same areas can expect another 1 to 3 inches of rain overnight.

In addition to the heavy rain, large hail is also a primary threat along with damaging winds and the possibility of tornadoes.

Flood watches extend for more than 1,000 miles from Oklahoma and northern Arkansas eastward to southern Missouri, southern Illinois, southern and central Indiana, Ohio and West Virginia. A flood watch means conditions are favorable for possible flooding, and it’s not a strong indication flooding will occur, the National Weather Service explained.

The significant flood threat is expected to shift from northwestern Arkansas to western Ohio on Friday. Storm totals between 2 and 4 inches of rain are expected, with the heaviest rainfall potentially exceeding 5 inches in total.

Meanwhile, northeast Louisiana, southeast Arkansas and western Mississippi are also at a moderate risk for severe thunderstorms that could bring strong and long-tracked tornadoes, large hail, and damaging wind gusts of more than 70 mph. Cities in the storm’s path include Jackson, Mississippi; Pine Bluff, Arkansas; and Monroe, Louisiana.

Additionally, the Storm Prediction Center has extended its slight risk for severe thunderstorms, a Level 2 of 5, from central Texas to southern Indiana through the overnight hours into Friday morning.

Cities including Fort Worth in Texas and Tulsa in Oklahoma are in the threat for strongest storms, while Dallas, Oklahoma City, St. Louis, Cincinnati and Louisville could potentially see storms overnight.