WAUSAU, Wis. (AP) – Strong thunderstorms have destroyed several barns and caused power outages in central Wisconsin.  Marathon County emergency management director Steve Hagman says the severe weather has damaged about a half-dozen rural properties near Colby, including several barns which were leveled. He says there are no reports of any injuries.  The National Weather Service reported wind gusts of up to 50 mph with heavy downpours and hail.        Wisconsin Public Service Corp. says nearly 4,700 customers lost power because of the storms.  Severe thunderstorm warnings were posted for Marathon, Lincoln, Langlade and Oneida counties Thursday morning.