Between the first downpour and the second, there was a brief and shining moment of optimism, and Ex Hex were the band who brought it to life. When the monsoon turned into a sprinkle, they took the stage and had time to pound out four quick songs of immaculate, revved-up power-pop. Then the stage director gave the cut-it-off-now sign, and everyone had to leave the park. It was fun while it lasted.