High humidity along with hot temperatures is making this week's heat wave in the central and eastern U.S. especially unhealthy. The dew point temperature is a measure of how much moisture is in the air. With dew points in the 60s, the air may be considered uncomfortable and in the 70s it becomes oppressive by diminishing a body's ability to sweat. In only rare cases will the dew points reach the 80s in the U.S. This movie shows average daily dew point data from the NAM model from July 18 through July 24, 2011.