ATLANTA (NewsNation Now) — Storms dumped as much as 6 inches of rain on Mississippi and Alabama on Tuesday ahead of threatening weather that forecasters said could include tornadoes across a large part of the South from Texas to Georgia.

With isolated flooding already being reported in western Alabama, the Storm Prediction Center said hail as large as tennis balls and intense twisters were possible across the region Wednesday. More than 6 million people live in an area stretching from eastern Arkansas to eastern Alabama that forecasters said was most at risk.

Forecasters issued tornado warnings in southwest Alabama as storms moved through early Tuesday, but no damage was reported immediately. Schools in Cullman County, north of Birmingham, delayed opening because of downpours. Rainfall was particularly intense around the Mississippi-Alabama state line, where as much as 6 inches fell.

On Wednesday, several tornadoes will be possible in a region that includes large parts of Arkansas, Mississippi, Alabama and parts of Louisiana and Tennessee, forecasters said.

The area at enhanced risk for severe storms Wednesday is home to more than 9 million people and includes the cities of Memphis, Tennessee; Birmingham, Alabama; and Jackson, Mississippi.

“Some of the tornadoes could become strong,” the National Weather Service in Jackson, Mississippi warned in its outlook for Wednesday’s storms.

In Alabama, strong tornadoes, golf ball-sized hail and winds of up to 60 mph will be possible on Wednesday, the weather service’s Birmingham office said.

Some Tuscaloosa residents and emergency responders are preparing for the potentially severe weather, NewsNation affiliate WIAT reported.

Tuscaloosa Fire Chief Randy Smith said the city is readying extra crews who will put up barricades or clear roads if needed.

In Alabama’s Clarke County, emergency officials are worried about the potential for toppling trees, NewsNation affiliate WKRG reported.

“We’re a large timber industry in this county there’s a large number of trees that are leaning. We’ve cleaned up a lot of those, cutting ‘leaners’ and hangers but there are still some out there,” said Clarke County EMA Director Roy Waite. 

More than a dozen Alabama school systems canceled classes, planned online sessions or announced early dismissals because of the threat. More could be added to the list. Storms likely will intensify in waves during the afternoon, forecasters said, and the worst wasn’t expected until overnight.

County officials are urging residents who live in mobile homes or RVs to make plans to stay in more secure locations if a tornado warning is issued.

Large, outdoor sites for administering COVID-19 vaccinations around Birmingham and Memphis canceled appointments because of the threat of severe weather. With people getting shots in their cars, officials were concerned that strong winds, rain, hail and the threat of tornadoes could make the operations unsafe.

The Associated Press and NewsNation affiliates WIAT and WKRG contributed to this report.