Degree Days:  A calculation used by utility companies to determine how much energy is used for heating or cooling.  They count one heating or cooling degree day, respectively, for each degree Fahrenheit below or exceeding 65: the temperature at which people are unlikely to run either heaters or conditioners.  Any day can have more than one cooling or heating degree day.

Dew Point:  The temperature at which air becomes saturated and moisture condenses into dew.

Dry Line:  A boundary separating warm, dry air from warm, humid air.

Relative Humidity:  An indicator of moisture in the air.  A 50 percent relative humidity means the air is half-saturated.