What is “Normal” Weather?

As seasons change, months end, and years come to a close, we often hear about how that particular period’s weather compares to normal. You may wonder, what is “normal”?

“Normal”  refers to the 30-year average of a particular meteorolgical variable, such as temperature or precipitation, in a specific location.  This average is a statistical number that gives us an idea of what to expect as well as a point of reference for historical comparisons.  These figures are useful to scientists who study climate change and to industries, such as power and construction, who utilize the data for planning purposes.

The “normals” are calculated every decade for the previous 30-year period by the National Climatic Data Center (NCDC),  a division of the National Oceanic and Atmospheric Administration.  They have a mandate from Congress dating back to 1890 to “… to establish and record the climatic conditions of the United States.”   In addition, the United States is a member of the U.N.’s World Meteorological Organization (WMO).  As a member nation, we follow their guidelines for computing 30-year averages.

The NCDC recently released their new “normals” based on the years 1981 to 2010.