Weather Resources - Glossary

Wondering what “graupel” is? Or how about “virga”? You have come to the right place. This section contains the definitions of several hundred weather related terms.

Please contact us if you have a suggestion for additional terms.

We have also developed a special glossary section with winter weather terms only.

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National Center for Atmospheric Research (NCAR) - A division of the University Corporation for Atmospheric Research, the Center plans, organizes, and conducts atmospheric and related research programs in collaboration with universities. For more information, contact NCAR, located in Boulder.

National Centers for Environmental Prediction (NCEP) - As part of the National Weather Service, the centers provide timely, accurate, and continually improving worldwide forecast guidance products. Some of the centers include the Aviation Weather Center, the Climate Prediction Center, the Storm Prediction Center, and the Tropical Prediction Center. Formerly known as NMC. For more information, contact the NCEP, with central offices located in Silver Spring, Maryland.

National Climatic Data Center (NCDC) - The agency that archives climatic data from the National Oceanic and Atmospheric Administration as well as other climatological organizations. For more information, contact the NCDC, located in Asheville, North Carolina.

National Hurricane Center (NHC) - A branch of the Tropical Prediction Center, it is the office of the National Weather Service that is responsible for tracking and forecasting tropical cyclones over the North Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific. For more information, contact the NHC, located in Miami, Florida.

National Oceanic and Atmospheric Administration (NOAA) - A branch of the U.S. Department of Commerce, it is the parent organization of the National Weather Service. It promotes global environmental stewardship, emphasizing atmospheric and marine resources. For further information, contact NOAA, headquartered in Silver Spring, Maryland.

National Severe Storms Laboratory (NSSL) - A branch of the National Oceanic and Atmospheric Administration, it provides accurate and timely forecasts and warnings of hazardous weather events, especially flash floods, hail, lightning, tornadoes, and other severe wind storms. For more information, contact the NSSL, headquartered in Norman, Oklahoma.

National Weather Association (NWA) - An organization whose membership promotes excellence in operational meteorology and related activities, recognizing the professional as well as the volunteer. For more information, contact the NWA

National Weather Service (NWS) - A primary branch of the National Oceanic and Atmospheric Administration, it is responsible for all aspects of observing and forecasting atmospheric conditions and their consequences, including severe weather and flood warnings. For more information, contact the NWS office in Boulder

Nautical Mile - A unit of length used in marine navigation that is equal to a minute of arc of a great circle on a sphere. One international nautical mile is equivalent to 1,852 meters or 1.151 statue miles.

Negative Vorticity Advection (NVA) - The advection of lower values of vorticity into an area.

NEXRAD - Acronym for NEXt Generation Weather RADar. A network of advanced Doppler radars implemented in the United States between 1992 and 1996, it detects the location and intensity of precipitation out to a range of 143 miles from the radar site. NEXRAD Doppler radar is highly sensitive and can detect precipitation from very light rain and snow up to the strongest thunderstorms with accuracy and detail. However, sometimes the radar's extreme sensitivity will cause ground clutter and other non-precipitation echoes to be displayed in the vicinity of the radar site.

Noctilucent Clouds - Rarely seen clouds of tiny ice particles that form approximately 75 to 90 kilometers above the earth's surface. They have been seen only during twilight (dusk and dawn) during the summer months in the higher latitudes. They may appear bright against a dark night sky, with a blue-silver color or orange-red.

Nocturnal Thunderstorms - Thunderstorms which develop after sunset. They are often associated with the strengthening of the low level jet and are most common over the Plains states. They also occur over warm water and may be associated with the seaward extent of the overnight land breeze.

Normal (or "average") - The recognized standard value of a meteorological element as it has been averaged in a given location over a fixed number of years. Normals are concerned with the distribution of data within limits of common occurrence. The parameters may include temperatures (high, low, and deviation), pressure, precipitation (rain, snow, etc.), winds (speed and direction), thunderstorms, amount of clouds, percent relative humidity, etc.

Nowcast - A short-term weather forecast for expected conditions in the next few hours.

Numerical Weather Prediction - The use of numerical models, such as the fundamental equations of hydrodynamics subjected to observed initial conditions, to forecast the weather. These models are run on high-speed computers at the National Centers for Environmental Prediction.

Portions of the 9NEWS Weather Glossary were taken from the second edition of the Glossary of Meteorology published by the American Meteorological Society (AMS). © 2009 American Meteorological Society