2011 U.S. annual relative humidities (Percent). Our humidity data were relative (and not absolute) humidities. Relative humidity is not measured directly, but can be estimated from temperature and dew point (dew point is measured) via
RH = exp 17.27 ( D - 32 ) 5 / 9  ( D - 32 ) 5 / 9 + 237.3      exp 17.27 ( T - 32 ) 5 / 9  ( T - 32 ) 5 / 9 + 237.3       100 % ,
where T is annual temperature, D is annual dew point, and exp is the exponential function [9]. As expected, the Southeast is the most humid region in the United States.