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Normal Weather
Wed Aug 06, 2003
Listen in RealAudio 
You've probably heard the term "normal" used by your local weathercaster to refer to the
benchmarks meteorologists and climatologists use to compare daily temperature and
precipitation values. You may hear phrases such as: "Today's high temperature was 10 degrees
above normal" or "Because of the drought we're experiencing, our total rainfall this month was
three inches below normal," but what exactly is "normal" weather?
Hi, I'm Bryan Yeaton and this is The Weather Notebook.
A "normal" is defined as a 30-year average of any meteorological element and can be useful in
describing the average weather for a particular location. Climate normals are computed on both
a daily and monthly basis for several thousand locations across the United States. The
National Climatic Data Center, or NCDC, in Asheville, NC is the nation's official keeper of
weather and climate records and has the responsibility of updating the official climate
normals every 10 years.
NCDC is currently in the process of releasing newly calculated normals for the period from
1971-2000. The previously used set of normals spanned the period from 1961-1990. The new
normals will determine 30-year averages of such weather elements as minimum and maximum
temperature and precipitation for nearly 8,000 locations across the United States.
Supplemental normals scheduled for release later this year will include such statistics as
freeze date probabilities, monthly precipitation probabilities, and temperature,
precipitation, and snowfall extremes.
Contrary to popular belief, "normal" weather is not necessarily what you should expect. It's
simply a statistical measure that helps put climate trends, such as drought or heat waves, in
a historical context.
Thanks today go to writer and meteorologist, Sean Potter. The Weather Notebook is a production
of the Mount Washington Observatory and is sponsored generously by Subaru of America and The
National Science Foundation.
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