A weather warning sign hangs near the 13th hole during the first round of the U.S. Open golf tournament at Merion Golf Club, Thursday, June 13, 2013, in Ardmore, Pa.

A weather warning sign hangs near the 13th hole during the first round of the U.S. Open golf tournament at Merion Golf Club, Thursday, June 13, 2013, in Ardmore, Pa.