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How low did the relative humidity get during the recent excessive heat episode in the Southwest?
-Paul Kubecka Berwyn
During the recent Southwest heat wave, Needles, California logged a temperature of 119 degrees in conjunction with a dew point of minus 11 yielding a desiccating relative humidity of 0.8 percent. As low as that is, even lower values have been observed. Meteorologist Dr. Jeff Masters cites two incredibly low relative humidities that vie for the world record. Earlier this month on June 20 at Safi-Abad Dezful, Iran with a temperature of 116 and a dew point of minus 28 the humidity dropped to 0.36 percent, virtually the same as a 0.33 percent value recorded at Needles on May 4, 2014 with temperature of 102 and a minus 36 dew point. Chicago’s lowest humidity is 13 percent, logged on several occasions, most recently April 14, 2015.