Powerful storms cause damage across several states (AP) - Apparent tornadoes destroyed houses, sent people to hospitals and tore up the roof of a maximum security prison in northern Alabama as bad weather threatened more twisters across the region Friday, two days after storms killed 13 people in the Midwest and South. Anxiety mounted from Georgia to southern Ohio across a wide swath where forecasters said strong storms could hit later in the day. Thousands of schoolchildren in several states were sent home as a precaution. Meanwhile, residents in parts of Illinois hit hard by the twisters earlier in the week were salvaging what they could from splintered homes. Storm damage was reported Friday in several states including Alabama, Indiana and Tennessee. In the Huntsville area, five people were taken to hospitals, and several houses were leveled by what authorities believed were tornadoes Friday morning. The extent of the people's injuries wasn't immediately known, and emergency crews were continuing to survey damage. No deaths were reported. At least 10 homes were damaged in a subdivision in Athens. Homeowner Bill Adams watched as two men ripped shingles off the roof of a house he rents out, and he fretted about predictions that more storms would pass through. "Hopefully they can at least get a tarp on it before it starts again," he said. Not far away, the damage was much worse for retired high school band director Stanley Nelson. Winds peeled off his garage door and about a third of his roof, making rafters and boxes in his attic visible from the street. "It's like it just exploded," he said. An apparent tornado also damaged a state maximum security prison about 10 miles from Huntsville, but none of the facility's approximately 2,100 inmates escaped. Part of the perimeter fence was knocked down, but the prison was secure. "It was reported you could see the sky through the roof of one of them," Corbett said. Authorities are confident that storms that hit Limestone and Madison counties were tornadoes, but it will be up to the National Weather Service to confirm the twisters, said Alabama State Emergency Management Agency spokeswoman Yasamie August. "We're still getting reports of damage pretty much as we speak," she said at midday. For residents and emergency officials across the state, tornado precautions and cleanup are part of a sadly familiar routine. A tornado outbreak last April killed about 250 people around the state, with the worst damage in Tuscaloosa to the south. Forecasters warned of severe thunderstorms with the threat of tornadoes crossing a region from southern Ohio through much of Kentucky and Tennessee. By early Friday afternoon, tornado watches covered parts of those states along with Missouri, Illinois and Indiana. In Norman, Okla., forecasters at the Storm Prediction Center said they were bracing for what could be a potent tornado outbreak. "Maybe five times a year we issue what is kind of the highest risk level for us at the Storm Prediction Center," forecaster Corey Mead said. This is one of those days. Mead said a powerful storm system was interacting with humid, unstable air that was streaming north from the Gulf of Mexico. "The environment just becomes more unstable and provides the fuel for the thunderstorms," Mead said. Schools sent students home early or cancelled classes entirely in states including Alabama, Tennessee, Mississippi, Kentucky and Indiana. In Alabama alone, more than 20 school systems dismissed classes early Friday. The University of Kentucky, the University of Louisville and several other colleges in the state also canceled classes. Residents were picking through debris in parts of Illinois that were devastated by the previous round of severe weather. The 9,000-resident town of Harrisburg was sacked by a twister about 5 a.m. Wednesday that killed six people. Forecasters weren't expecting the area to be hit hard by the newest storms, though. That forecast didn't much matter to Amanda Patrick, who lost her home Wednesday in the same twister that killed neighbors. Associated Press writers Jim Suhr in Harrisburg, Ill., and Jeff Martin in Atlanta contributed to this report.