POLK COUNTY—Severe thunderstorms that moved through Polk County Thursday evening and continued into early Friday morning left more than 1,400 customers without power. The National Weather Service issued severe thunderstorm warnings late Thursday, forecasting wind gusts of up to 60 mph and possible damage to trees and power lines. As of Friday morning, 993 Duke Energy customers and 431 Rutherford Electric Membership Corp. customers were without p…