Source: National Oceanic and Atmospheric Administration (NOAA). Updated Monthly and Annual. http://www.noaa.gov
Definitions: Precipitation: Average annual precipitation is the average of the annual amount of precipitation for a location over a year. The precipitation for each month at a location is added and divided by 12 to get the average annual precipitation for a given location.
Degree days: A degree day gauges the amount of heating or cooling needed for a building using 65 degrees as a baseline. To compute heating/cooling degree-days, take the average temperature for a day and subtract the reference temperature of 65 degrees. If the difference is positive, it is called a "Cooling Degree Days". If the difference is negative, it is called a "Heating Degree Days". The magnitude of the difference is the number of days. For example, if your average temperature is 50 degrees for a day in September, the difference of the average temperature for that day and the reference temperature of 65 degrees would yield a minus 15. Therefore, you know that you are going to have Heating Degree Days that day. Since the magnitude of the difference is 15, you know that you are going to have 15 Heating Degree Days. Electrical, natural gas, power, and heating, and air conditioning industries utilize heating and cooling degree information to calculate their needs.
Temperature: A measure of the warmth of the ambient air measured by a suitable instrument such as as a thermometer.
Scope and Methodology: The climatological normals are based on monthly maximum, minimum, and mean temperature and monthly total precipitation records for each year in the 30-year period. A climate normal is defined, by convention, as the arithmetic mean of a climatological element computed over three consecutive decates.