BIRMINGHAM, Ala.—A wave of storms pounded the Deep South on Wednesday, leaving a trail of splintered trees and damaged buildings, and forecasters said still stronger ones were on the way with the potential for massive tornadoes, downpours and hail the size of baseballs. While nearly 16 million people in the Southeast could see powerful storms, the Storm Prediction Center said, a region of about 3 million stretching from southeastern Arkansas and northeastern Louisiana across Mississippi into Alabama was at high risk for big twisters that stay on the ground for miles, straight winds up to 80 mph and destructive hail. Possible tornadoes knocked down trees, toppled power lines and damaged homes in rural Chilton County and the Alabama communities of Burnsville and Moundville, where power was out and trees blocked a main highway. “Downtown Moundville got it. Some roofs and stuff got taken off houses,” said Michael Brown, whose family …