The product is produced by meteorological models that incorporate all available surface observations. Such information may be important for drought stress on crops, highway conditions, and heat stress on people. The product will be most accurate in areas with relatively uniform terrain. Relative humidity is a quantity that is sometimes misused by the media. As temperature increases, so does the amount of moisture the air is capable of holding.
Relative humidity tends to increase at night and decrease during the day.
The greatest limitation will occur when surface observations are sparse or missing. The meteorological models will attempt to fill in time or space gaps, but error may be introduced, especially in complex terrain or rapidly changing weather patterns. In particular, localized high relative humidity can occur in the rain-cooled area around thunderstorms, or during the nighttime in river valleys. Overlays such as winds and lightning strikes may be useful for assessing fire danger. A second window with topography or radar imagery may help determine areas that may be experiencing localized changes in relative humidity.