Mean Monthly and Annual Average Relative Humidity
Conterminous United States

Statistic: 30-year average daily mean relative humidity
Time period: 1961-1990 
Time period: 1961-1990
Time interval: monthly
Spatial format: grid
Data format: ARC/Info ASCII GRID

Projection: Geographic
Spatial resolution: 1.25 arc-minutes (~2 km)
Spatial Extent: Conterminous United States
Units: Percent

Date created: August 2000
Methods: Calculated from mean ambient temperature and mean dew point temperature, and Gaussian filter resolution enhancement. See FGDC-compliant metadata for details. 


Mean daily relative humidity,
November, entire region
Mean daily relative humidity, July, southern California
  • Reviewed and approved by the US National Climatic Data Center 
  • Incorporates topographic effects on relative humidity 
  • Includes coastal and lake effects on relative humidity 
  • Accounts for inversions on coasts and in inland valleys 
  • Consistent treatment and spatial quality control of station data 
  • Consistent coverage across all state boundaries 
  • "Universal" geographic (latitude/longitude) projection allows conversion to any other coordinate system 
  • Data format allows for easy import into ESRI's GIS products, as well as MAPINFO and Intergraph's GeoMedia 

Data used in analysis

  • 220 National Weather Service stations for relative humidity 
  • 6,420 stations for temperature 
  • 560 stations for dew point
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