NAM - see North American Mesoscale Model

Narrowband Data - the collection of data products transmitted from the WSR-88D Radar Product Generator to a Principal User Processor or to a NIDS vendor for external distribution

National Center for Atmospheric Research (NCAR) - part of the University Corporation for Atmospheric Research (UCAR). It is comprised of university scientists that work together on weather research. The main areas of research and tools include atmospheric chemistry, climate, cloud physics and storms, weather hazards to aviation, and interactions between the sun and earth.

National Centers for Environmental Prediction (NCEP) - the modernized version of the National Meteorological Center, located near Washington, D.C. It is a part of the National Weather Service and prepares national forecasts and outlooks of weather and climate, mainly as guidance to NWS forecasters. It is made up of nine national centers: Aviation Weather Center, Climate Prediction Center, Environmental Modeling Center, Hydrometeorological Prediction Center, NCEP Central Operations, Ocean Prediction Center, Space Weather Prediction Center, Storm Prediction Center, and Tropical Prediction Center.

National Climatic Data Center (NCDC) - the agency that archives climate data from the National Oceanic and Atmospheric Administration (NOAA), as well as other climatological organizations

National Hurricane Center (NHC) - one of three branches of the Tropical Prediction Center (TPC). This center prepares and distributes hurricane watches and warnings for the general public for tropical cyclones over the Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific from May 15 through November 30. The group also provides training for emergency managers and does research on improving hurricane forecasting techniques.

National Meteorological Center (NMC) - the old version of the National Centers for Environmental Prediction (NCEP)

National Oceanic and Atmospheric Administration (NOAA) - a Federal Government agency under the Department of Commerce that covers both ocean and atmospheric domains.

National Severe Storms Forecast Center (NSSFC) - was in Kansas City, MO; now the Storm Prediction Center in Norman, OK

National Severe Storms Laboratory (NSSL) - a NOAA lab that leads the way in investigations of all aspects of severe weather. The main headquarters are in Norman, OK, with staff in Colorado, Nevada, Washington, Utah, and Wisconsin. They are dedicated to improving severe weather warnings and forecasts in order to save lives and reduce property damage.

National Weather Center (NWC) - a collection of Federal, State, and university meteorology groups located in one building in Norman, OK.

National Weather Service (NWS) - an agency of the Federal Government within the Department of Commerce, National Oceanic and Atmospheric Administration, which is responsible for providing observations, forecasts and warnings of meteorological and hydrological events in the interest of national safety and economy.

NBND - northbound

NC - no change

NC - North Carolina

NCAR - see National Center for Atmospheric Research

NCDC - see National Climatic Data Center

NCEP - see National Centers for Environmental Prediction

NCEP Central Operations (NCO) - one of nine NCEP centers. This center works on numerical weather models and prepares products for dissemination. It is located in Camp Springs, Maryland.

NCO - see NCEP Central Operations

ND - North Dakota

NDVI - see Normalized Difference Vegetation Index

NE - Nebraska

NE - northeast

Near-Infrared Radiation - a type of electromagnetic radiation having a slightly higher wavelength than visible radiation

NEC - necessary

NEG - negative

Negative-Tilt Trough - an upper level low pressure system that is tilted to the west with increasing latitude (i.e., with an axis from southeast to northwest); often it is a sign of a developing or intensifying system

Negative Area - the area on a sounding representing the layer in which a lifted parcel would be cooler than the environment; thus, the area between the path of the lifted parcel and the environmental temperature profile. See Convective Inhibition.

Negative Vorticity Advection (NVA) - the advection of lower values of vorticity into an area. NVA is usually associated with sinking air. Also referred to as Anticyclonic Vorticity Advection (AVA), the opposite of Cyclonic Vorticity Advection (CVA).

NELY - northeasterly

NERN - northeastern

Nested Grid Model (NGM) - one of the operational forecast models run at NCEP; the NGM is run twice daily, with forecast output out to 48 hours

Net Solar Radiation - the difference between the downward and upward fluxes of solar radiation

Net Terrestrial Radiation - the difference between the downward and upward fluxes of terrestrial radiation

NEWD - northeastward

Newton’s First Law of Motion - an object will stay at rest or continue at a constant speed and direction (constant velocity means no acceleration) unless an external force acts on it. This is also known as the Law of Inertia. For an object to accelerate or change direction, an unbalanced force [also known as a net force (the sum of the forces is non-zero)] must be applied. A balanced force means that you have forces that are of equal magnitude and in opposite directions (see Newton’s Third Law). An unbalanced force is one that does not have a corresponding force that acts in an opposite direction or with an equal magnitude.

Newton’s Second Law of Motion - the net force (total force) on an object is equal to the mass of the object multiplied by its acceleration (F=ma). The acceleration of an object depends directly upon the net force acting upon the object and inversely upon the mass of the object. For example, if a force acting upon an object is increased, the acceleration is increased. If the mass is increased, the acceleration of the object is decreased.

Newton’s Third Law of Motion - for every action there is an equal, but opposite reaction. In every interaction, there is a pair of forces acting on the two interacting objects. These two forces are equal in size (magnitude) and opposite in direction.

NEXRAD - see NEXt-Generation Weather RADar

NEXRAD Information Dissemination Service (NIDS) - a system whereby four commercial vendors have the exclusive right to distribute a certain subset of NEXRAD products to agencies outside the DoD, NWS, and FAA. OK-First has moved away from NIDS and now gets radar data directly from a NOAAport feed.

Next-Generation Weather Radar (NEXRAD) - a network of high-resolution Doppler radars operated by the NWS; NEXRAD units are known as WSR-88D

NGM - see Nested Grid Model

NGT - night

NH - New Hampshire

NHC - see National Hurricane Center

NIDS - see NEXRAD Information Dissemination Service

NIL - none

Nimbostratus (NS) - a gray colored and often dark cloud accompanied by more or less continuously falling rain, snow, sleet, etc. This cloud usually does not contain lightning, thunder, or hail

Nitrogen - a colorless, tasteless, odorless gas that constitutes 78% of the atmosphere by volume and occurs as a constituent of all living tissues in combined form

NJ - New Jersey

NLY - northerly

NM - New Mexico

NMBR - number

NMC - see National Meteorological Center

NML - normal

NMRS - numerous

NOAA - see National Oceanographic and Atmospheric Administration

Noctilucent Clouds - wavy, thin, bluish-white clouds that are best seen at twilight in polar latitudes. They form at altitudes about 80 to 90 km (50 to 56 mi) above the Earth’s surface.

Nocturnal (or Radiational) Inversion - a temperature inversion that develops during the night as a result of radiational cooling of the surface. Because the immediate surface (lower Boundary Layer) cools much more rapidly during radiational cooling conditions than the air just above (upper Boundary Layer), a temperature inversion can be created overnight, but typically erodes quickly after sunrise (due to rising thermals and the resultant turbulence).

Nocturnal Radiation - see Effective Terrestrial Radiation

Non-Coherent Radar - a conventional radar in which the phase of the transmitted radiation is not known

Normal - a 30-year average of values that gives scientists a "best guess" of weather conditions for an area.

Normalized Difference Vegetation Index (NDVI) - an index produced using AVHRR data from NOAA polar orbiting satellites. The index is used for monitoring vegetation changes over large areas with a resolution up to 1 km.

Normal Temperature - a 30-year average of temperatures. It is not what is "expected" or what "should" happen.

North American Mesoscale Model (NAM) - a model that runs four times a day (00, 06, 12, 18 UTC) and goes out 84 hours with each run. This model used to be known as the Eta Model.

Northern Lights - see Aurora Borealis

Nowcasting - short-term weather forecasting for the near future, generally from minutes up to a few hours in the future

NR - near

NRN - northern

NRW - narrow

NS - see Nimbostratus

NSSFC - see the National Severe Storms Forecast Center

NSSL - see National Severe Storms Laboratory

Numerical Model - a mathematical representation of a process, system, or object developed to understand its behavior or to make predictions, created by computers. The representation always involves certain simplifications and assumptions.

Numerical Weather Prediction (NWP) - the forecasting of the evolution of atmospheric disturbances by computational methods on a computer

NV - Nevada

NVA - see Negative Vorticity Advection

NW - northwest

NWC - see National Weather Center

NWD - northward

NWLY - northwesterly

NWP -see Numerical Weather Prediction

NWRD - northwestward

NWRN - northwestern

NWS - see National Weather Service

NXT - next

NY - New York

Nyquist Velocity - see Maximum Unambiguous Velocity