Heat dome brings extreme temps and humidity to the East, prompting early school dismissals  NBC NewsIowa school closings: Iowa districts closing early due to sweltering heat  KCCI Des MoinesTriple-digit heat strikes again: Late summer heat to scorch millions  USA TODAYHeat wave roasts more than 50 million from Ohio Valley to Washington D.C.  AxiosTens of millions bake under extreme heat in eastern United States  Yahoo! Voices