Nautical DuskThe time at which the sun is 12 degrees below the horizon in the evening. At this time, objects are no longer distinguishable.
Nautical MileA unit of distance used in marine navigation and marine forecasts. It is equal to 1.15 statue miles or 1852 meters.
Nautical TwilightThe time after civil twilight, when the brighter stars used for celestial navigation have appeared and the horizon may still be seen.
Navigation MethodsThree basic methods of providing and managing inland waterways - 1) Run-of-the-River: no provision of upstream storage; 2) Slack-Water: locks and dams…
NAVTEXAn international automated medium frequency (518 kHz) direct-printing service for delivery of navigational and meteorological warnings and forecasts, as…
NAVTEX Forecast(NAV) - A National Weather Service marine forecast combining various Coastal Waters and Offshore forecasts, optimized to accommodate transmission via…
NCEPNational Centers for Environmental Prediction. A part of the National Weather Service which provides nationwide computerized and manual guidance to…
Neap TideA minimum tide occurring at the first and third quarters of the moon.
Near Real TimeWhen referred to in textual references, the ARM conception of "near-real time" is "with a few hours delay."
near-surface soil heat fluxA quantity measured near the surface of the soil, according to the formula B = λ(dT/dz), where λ is the conductivity of the soil that the heat or…
near-surface soil moisture fluxA quantity measured near the surface of the soil, according to the formula B = λ(dq/dz), where λ is the conductivity of the soil that the heat or…
Nearshore Forecast(NSH) - National Weather Service seasonal marine forecasts for an areas of the Great Lakes extending from a line approximating mean low water datum along…
NESDISNational Environmental Satellite, Data, and Information Service. NESDIS collects, processes, stores, analyzes, and disseminates various types of…
Net All-Wave RadiationThe net or resultant value of the upward and downward longwave and shortwave radiative fluxes through a plane at the earth-atmosphere interface; a…
net radiationThe difference between upwelling and downwelling, covering longwave and shortwave radiation.
Net RainfallThe portion of rainfall which reaches a stream channel or the concentration point as direct surface flow.
Net terrestrial radiationNet terrestrial radiation Difference between the downward and upward terrestrial radiation fluxes; net flux of terrestrial radiation.
Neutral LineThe line that separates longitudinal magnetic fields of opposite polarity.
Neutral StabilityAn atmospheric condition that exists in unsaturated air when the environmental lapse rate equals the dry adiabatic rate, or in saturated air when the…
Nimbostratus(abbrev. NS)- A cloud of the class characterized by a formless layer that is almost uniformly dark gray; a rain cloud of the layer type, of low altitude…
nitrogenA colorless, tasteless element that comprises four-fifths of the atmosphere by volume, denoted by N2.
Nitrogen cycleCyclic movement of nitrogen in different chemical forms from the environment, to organisms, and then back to the environment.
Nitrogen fixationThe conversion of atmospheric nitrogen to biologically usable nitrates.
Nitrogen Oxides (NOx)(NOx)The products of all combustion processes formed by the combination of nitrogen and oxygen.
Nitrous Oxide (N2O)A powerful greenhouse gas with a global warming potential of 296 times that of carbon dioxide (CO2).
NOAANational Oceanic and Atmospheric Administration
NOAA Weather Radio"The voice of the National Weather Service" - NOAA Weather Radio broadcasts National Weather Service warnings, watches, forecasts and other hazard…
NOAA Weather WireMass dissemination via satellite of National Weather Service products to the media and public.
Noctilucent CloudsWavy, thin, bluish-white clouds that are best seen at twilight in polar latitudes. They form at altitudes about 80 to 90 km above the Earth's surface.
NocturnalRelated to nighttime; occurring at night.
Nocturnal InversionUsed interchangably with Radiational Inversion; a temperature inversion that develops during the night as a result of radiational cooling of the surface.
Nocturnal JetThis wind speed maximum occurs just above the nocturnal inversion at night. It is typically found in the south central United States during the late…
Nocturnal ThunderstormsThunderstorms which develop after sunset. They are often associated with the strengthening of the low level jet and are most common over the Plains states.
NOGAPSNavy Operational Global Atmospheric Prediction System; a 144-hour numerical model of the atmosphere run by the U.S. Navy twice daily.
NOHRSCIn hydrologic terms, the National Operational Hydrologic Remote Sensing Center.
non-lineara system that is not describable as the sum of its parts and, as a result, is difficult to predict.
Non-point sourceLarge land area such as crop fields and urban areas that discharge pollutant into surface and underground water over a large area. See point source.
Non-Uniform Sky ConditionA localized sky condition which varies from that reported in the body of the report.
Non-Uniform VisibilityA localized visibility which varies from that reported in the body of the report.
Nonattainment AreaThe EPA's designation for an air quality control region (or portion thereof) in which ambient air concentrations of one or more criteria pollutants exceed…
NonbiodegradableSubstance that cannot be broken down in the environment by natural processess. See biodegradable.
NonlinearitiesOccur when changes in one variable cause a more than proportionate impact on another variable.
Nor\'easterA strong low pressure system that affects the Mid Atlantic and New England States. It can form over land or over the coastal waters.
NormalThe long-term average value of a meteorological paramater (i.e., temperature, humidity, etc.) for a certain area.
Normal Water Surface ElevationIn hydrologic terms, the lowest crest level of overflow on a reservoir with a fixed overflow level (spillway crest elevation).
Normal YearA year during which the precipitation or stream flow approximates the average for a long period of record.
North American HighNorth American High The relatively weak general area of high pressure which, as shown on mean charts of sea-level pressure, covers most of North America…
North Atlantic Oscillation(Abbrev. NAO) - the NAO is a large-scale fluctuation in atmospheric pressure between the subtropical high pressure system located near the Azores in the…
North Pacific HighA semi-permanent, subtropical area of high pressure in the North Pacific Ocean.
North Slope of Alaska (NSA) site(NSA)The third ARM research site, the NSA locale has is located in Barrow, Alaska. Its polar regions are predicted to undergo the largest warming in response…
North WallThe north side boundary of the Gulf Stream generally extending northeast from Cape Hatteras where the Gulf Stream turns northeast.
Northern LightsCommon name for Aurora Borealis; the luminous, radiant emission from the upper atmosphere over middle and high latitudes, and centred around the earth's…
NowcastA short-term weather forecast, generally out to six hours or less. This is also called a Short Term Forecast.
NSNimbostratus- A cloud of the class characterized by a formless layer that is almost uniformly dark gray; a rain cloud of the layer type, of low altitude…
NSSLNational Severe Storms Laboratory - this is one of NOAA's internationally known Environmental Research Laboratories, leading the way in investigations of…
Nuclear electric powerElectricity generated by an electric power plant whose turbines are driven by steam generated in a reactor by heat from the fissioning of nuclear fuel.
Nuclear EnergyEnergy that comes from splitting atoms of radioactive materials, such as uranium, and which produces radioactive wastes.
Numerical ForecastingA computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids.
Numerical Weather PredictionSame as Numerical Forecasting; a computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids.
NumerousA National Weather Service convective precipitation descriptor for a 60 or 70 percent chance of measurable precipitation (0.01 inch).
NVANegative Vorticity Advection - the advection of lower values of vorticity into an area.