Authorities are investigating the damage left behind by spring storms carrying more than a dozen suspected tornadoes that swept across the southern Plains, bringing floods, forcing the evacuation of an international airport and destroying homes near Oklahoma City.At least 12 people were injured, but no deaths were immediately reported from the twisters that also hit rural parts of Texas, Kansas and Nebraska on Wednesday night. The Oklahoma City area seemed to be the hardest hit. A twister destroyed homes in Grady County, southwest of the city, and it appeared another tornado touched down in the area later Wednesday evening when a second storm came through.