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Normal Weather
Thu Aug 11, 2005
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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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