• Weather Glossary (N)

    From Daryl Stout@618:250/33 to All on Fri Apr 16 00:04:27 2021
    This weather glossary contains information on more than 2000 terms,
    phrases and abbreviations used by the National Weather Service (NWS)...
    the government agency who makes weather forecasts, and issues weather advisories, watches, and warnings, for the United States, and its
    territories.

    Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and
    before many NWS products were directly available to the public. It is the purpose of this glossary to aid you in better understanding NWS products.

    ***

    N
    North

    Nacreous Clouds
    Clouds of unknown composition that have a soft, pearly luster and that
    form at altitudes about 25 to 30 km above the Earth's surface. They are
    also called "mother-of-the-pearl clouds."

    Nadir
    The point on any given observer's celestial sphere diametrically opposite
    of one's zenith.

    NAM
    The operational North Amercian Meso (NAM, formerly Eta) is run four times
    per day (00,06,12,18Z), all cycles run to 84-h.

    Nanotesla (nT)
    A unit of magnetism equal to 10-9 tesla, equivalent to a gamma
    (10-5 gauss).

    NAO
    North Atlantic Oscillation - the NAO is a large-scale fluctuation in atmospheric pressure between the subtropical high pressure system located
    near the Azores in the Atlantic Ocean and the sub-polar low pressure
    system near Iceland and is quantified in the NAO Index. The surface
    pressure drives surface winds and wintertime storms from west to east
    across the North Atlantic affecting climate from New England to western
    Europe as far eastward as central Siberia and eastern Mediterranean and southward to West Africa.

    NAO Index
    This index measures the anomalies in sea level pressure between the
    Icelandic low pressure system and the Azores high pressure system in the
    North Atlantic Ocean.

    When the NAO is in its is positive phase (+NAO), the northeastern United
    States sees an increase in temperature and a decrease in snow days; the
    central US has increased precipitation, the North Sea has an increase in storms; and Norway along with Northern Europe has warmer temperatures and increased precipitation.

    When the NAO is in its negative phase (-NAO), the Tropical Atlantic and
    Gulf coast have increased number of strong hurricanes; northern Europe is drier, and Turkey along with other Mediterranean countries has increased precipitation.

    National Ambient Air Quality Standards
    In the United States, national standards for the ambient concentrations
    in air of different air pollutants designed to protect human health and welfare.

    National Climatic Data Center
    The agency that archives climatic data from the National Oceanic and Atmospheric Administration, as well as other climatological organizations.

    National Digital Forecast Database
    (NDFD)- The National Weather Service's NDFD provides access to gridded forecasts of sensible weather elements (e.g., wind, wave height) through
    the National Digital Forecast Database (NDFD). NDFD contains a seamless
    mosaic of digital forecasts from NWS field offices working in
    collaboration with the National Centers for Environmental Prediction
    (NCEP). The database is made available to all customers and partners from
    the public, private and academic sectors. Those customers and partners
    may use this data to create a wide range of text, graphic, gridded and
    image products of their own.

    National Fire Danger Rating System
    A uniform fire danger rating system used in the United States that
    focuses on the environmental factors that impact the moisture content
    of fuels. Fire danger is rated daily over large administrative areas,
    such as national forests.

    National Flood Summary
    This NWS daily product (abbreviated FLN) contains nationwide information
    on current flood conditions. It is issued by the Hydrometeorological Information Center of the Office of Hydrology.

    National Hurricane Center
    One of three branches of the Tropical Prediction Center (TPC). This
    center maintains a continuous watch on tropical cyclones over the
    Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific from 15 May through November 30. The Center prepares and distributes hurricane
    watches and warnings for the general public, and also prepares and
    distributes marine and military advisories for other users. During the "off-season" NHC provides training for U.S. emergency managers and representatives from many other countries that are affected by
    tropical cyclones. NHC also conducts applied research to evaluate and
    improve hurricane forecasting techniques, and is involved in public
    awareness programs.

    National Hurricane Operations Plan
    (NHOP) - The NHOP is issued annually by the Federal Coordinator for Meteorological Services and Supporting Research. It documents
    interdepartmental agreements relating to tropical cyclone observing,
    warning, and forecasting services. National Hurricane Center (NHC),
    Central Pacific Hurricane Center (CPHC), and the JTWC serve as the
    principal offices in coordinating the day-to-day activities of the NWS
    in support of the Plan in their region of responsibility.

    National Severe Storms Laboratory
    This is one of NOAA's internationally known Environmental Research Laboratories, leading the way in investigations of all aspects of
    severe weather. Headquartered in Norman OK with staff in Colorado,
    Nevada, Washington, Utah, and Wisconsin, the people of NSSL, in
    partnership with the National Weather Service, are dedicated to
    improving severe weather warnings and forecasts in order to save
    lives and reduce property damage.

    National Weather and Crop Summary
    A product of the National Agricultural Statistics Service,
    Agricultural Statistics Board, and U.S. Department of Agriculture.
    It contains weekly national agricultural weather summaries,
    including the weather's effect on crops; summaries and farm progress
    for 44 states and New England area.

    Natural Control
    In hydrologic terms, a stream gaging control which is natural to the
    stream channel, in contrast to an artificial control structure by man.

    Nautical Dawn
    The time at which the sun is 12 degrees below the horizon in the
    morning. Nautical dawn is defined as that time at which there is just
    enough sunlight for objects to be distiguishable.

    Nautical Dusk
    The time at which the sun is 12 degrees below the horizon in the
    evening. At this time, objects are no longer distinguishable.

    Nautical Mile
    A unit of distance used in marine navigation and marine forecasts. It
    is equal to 1.15 statue miles or 1852 meters. It is also the length of
    1 minute of latitude.

    Nautical Twilight
    The time after civil twilight, when the brighter stars used for
    celestial navigation have appeared and the horizon may still be seen.
    It ends when the center of the sun is 12 degrees below the horizon,
    and it is too difficult to perceive the horizon, preventing accurate
    sighting of stars.

    Navigation Methods
    In hydrologic terms, there are three basic methods of providing and
    managing inland waterways -

    1) Run-of-the-River: no provision of upstream storage;

    2) Slack-Water: locks and dams provide slack water or pools with
    adequate depth for the draft of heavy barges and area to prevent
    excessive velocities;

    3) Canalization: in lieu of a series of dams on the river a canal with
    locks adjoins the river.

    NAVTEX
    An international automated medium frequency (518 kHz) direct-printing
    service for delivery of navigational and meteorological warnings and
    forecasts, as well as urgent marine safety information to ships. It
    was developed to provide a low-cost, simple, and automated means of
    receiving this information aboard ships at sea within approximately
    200 nautical miles of shore and is an element of the Global Maritime
    Distress and Safety System (GMDSS). NAVTEX stations in the U.S. are
    operated by the U.S. Coast Guard. There are no user fees associated
    with receiving NAVTEX broadcasts. The International System uses the
    frequency of 518 kHz worldwide and optional National Systems use
    frequencies of 490 and 4205.5 kHz. Safety messages on 518 kHz have
    to be in the English language worldwide but broadcasts on the 490 and
    4209.5 kHz frequency can be in the local language.

    NAVTEX Forecast
    (NAV) - A National Weather Service marine forecast combining various
    Coastal Waters and Offshore forecasts, optimized to accommodate
    transmission via NAVTEX.

    NBND
    Northbound

    NC
    1. No change

    2. North Carolina

    NCAR
    National Center for Atmospheric Research

    NCCF
    NOAA Central Computer Facility

    NCDC
    National Climatic Data Center

    NCEP
    National Centers for Environmental Prediction. A part of the National
    Weather Service which provides nationwide computerized and manual
    guidance to Warning and Forecast Offices concerning the forecast of
    basic weather elements.

    NDBC
    National Data Buoy Center

    NDFD
    (National Digital Forecast Database) - The National Weather Service's
    NDFD provides access to gridded forecasts of sensible weather elements
    (e.g., wind, wave height) through the National Digital Forecast
    Database (NDFD). NDFD contains a seamless mosaic of digital forecasts
    from NWS field offices working in collaboration with the National
    Centers for Environmental Prediction (NCEP). The database is made
    available to all customers and partners from the public, private and
    academic sectors. Those customers and partners may use this data to
    create a wide range of text, graphic, gridded and image products of
    their own.

    NE
    Northeast

    Neap Tide
    A minimum tide occurring at the first and third quarters of the moon.

    Nearshore Forecast
    (NSH) - National Weather Service seasonal marine forecasts for an area
    of the Great Lakes extending from a line approximating mean low water
    datum along the coast or an island, including bays, harbors, and sounds,
    out to 5 nm. These forecasts are normally issued from Daylight Savings
    Time approximately April 7 through December 31, though the dates may be shortened or extended based on local/regional requirements.

    NEC
    Necessary

    NEG
    Negative

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

    Negative-tilt Trough
    An upper level system which is tilted to the west with increasing
    latitude (i.e., with an axis from southeast to northwest). A
    negative-tilt trough often is a sign of a developing or intensifying
    system.

    NELY
    Northeasterly

    NERN
    Northeastern

    NESDIS
    National Environmental Satellite, Data, and Information Service. NESDIS collects, processes, stores, analyzes, and disseminates various types
    of hydrologic, meteorologic, and oceanic data. NESDIS is also
    responsible for the development of analytical and descriptive products
    so as to meet the needs of its users.

    Net All-Wave Radiation
    The net or resultant value of the upward and downward longwave and
    shortwave radiative fluxes through a plane at the earth-atmosphere
    interface; a component of the surface energy budget.

    Net Rainfall
    In hydrologic terms, the portion of rainfall which reaches a stream
    channel or the concentration point as direct surface flow.

    Neutral Line
    The line that separates longitudinal magnetic fields of opposite
    polarity.

    Neutral Stability
    An atmospheric condition that exists in unsaturated air when the
    environmental lapse rate equals the dry adiabatic rate, or in saturated
    air when the environmental lapse rate equals the moist adiabatic rate.

    NEWD
    Northeastward

    NEXRAD
    NEXt Generation RADar. A NWS network of about 140 Doppler radars
    operating nationwide.

    NGM
    The Nested Grid Model, a 48-hour numerical model of the atmosphere run
    twice daily by NCEP.

    NGT
    Night

    NHC
    National Hurricane Center - one of three branches of the Tropical
    Prediction Center (TPC). This center maintains a continuous watch on
    tropical cyclones over the Atlantic, Caribbean, Gulf of Mexico, and the
    Eastern Pacific from 15 May through November 30. The Center prepares
    and distributes hurricane watches and warnings for the general public,
    and also prepares and distributes marine and military advisories for
    other users. During the "off-season" NHC provides training for U.S.
    emergency managers and representatives from many other countries that
    are affected by tropical cyclones. NHC also conducts applied research
    to evaluate and improve hurricane forecasting techniques, and is
    involved in public awareness programs.

    NHOP
    (National Hurricane Operations Plan) - The NHOP is issued annually by
    the Federal Coordinator for Meteorological Services and Supporting
    Research. It documents interdepartmental agreements relating to
    tropical cyclone observing, warning, and forecasting services. National Hurricane Center (NHC), Central Pacific Hurricane Center (CPHC), and
    the JTWC serve as the principal offices in coordinating the day-to-day activities of the NWS in support of the Plan in their region of
    responsibility.

    Nieve Penitente
    A spike or pillar of compacted snow, firn or glacier ice, caused by differential melting and evaporation. The pillars form most frequently
    on low-latitude mountains where air temperatures are near freezing,
    dew points are much below freezing and insolation is strong. Penitents
    are oriented individually toward the noon-day sun, and usually occur
    in east-west lines.

    Night
    The period of the day between dusk and dawn.

    NIL
    None

    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, usually below 8000 ft (2400 m).

    NLY
    Northerly

    NM
    Nautical Miles

    NMBR
    Number

    NMC
    National Meteorological Center

    NML
    Normal

    NMRS
    Numerous

    NOAA
    National 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 information 24 hours a day. It is provided as a
    public service by NOAA. The NOAA Weather Radio network has more
    than 480 stations in the 50 states and near adjacent coastal waters,
    Puerto Rico, the U.S. Virgin Islands and U.S. Pacific Territories.
    It operates between 162.40 and 162.55 Megahertz on the Public Service
    Band.

    NOAA Weather Wire
    Mass dissemination via satellite of National Weather Service products
    to the media and public.

    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 above the
    Earth's surface.

    Nocturnal
    Related to nighttime; occurring at night.

    Nocturnal Inversion
    Used interchangably with 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.

    Nocturnal Jet
    This wind speed maximum occurs just above the nocturnal inversion at
    night. It is typically found in the south central United States during
    the late spring and summer months. It is important in the development
    of Mesoscale Convective Complexes (MCC) or Mesoscale Convective Systems
    (MCS).

    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.

    NOGAPS
    Navy Operational Global Atmospheric Prediction System; a 144-hour
    numerical model of the atmosphere run by the U.S. Navy twice daily.

    NOHRSC
    In hydrologic terms, the National Operational Hydrologic Remote Sensing
    Center. An organization under the National Weather Service Office of
    Hydrology (OH) that mainly deals with snow mapping.

    Non-Uniform Sky Condition
    A localized sky condition which varies from that reported in the body
    of the report.

    Non-Uniform Visibility
    A localized visibility which varies from that reported in the body of
    the report.

    Nonattainment Area
    An area that does not meet ambient air quality standards.

    Normal
    The long-term average value of a meteorological paramater (i.e.,
    temperature, humidity, etc.) for a certain area. For example,
    "temperatures are normal for this time of year" means that temperatures
    are at or near the average climatological value for the given date.
    Normals are usually taken from data averaged over a 30-year period
    (e.g., 1971-2000 average), and are concerned with the distribution of
    data within limits of common occurrence.

    Normal Water Surface Elevation
    In hydrologic terms, the lowest crest level of overflow on a reservoir
    with a fixed overflow level (spillway crest elevation). For a reservoir
    whose outflow is controlled wholly or partly by movable gates, siphons,
    or other means, it is the maximum level to which water may rise under
    normal operating conditions, exclusive of any provision for flood
    surcharge.

    Normal Year
    A year during which the precipitation or stream flow approximates the
    average for a long period of record.

    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 Atlantic Ocean and the sub-polar low pressure system near
    Iceland and is quantified in the NAO Index. The surface pressure drives
    surface winds and wintertime storms from west to east across the North
    Atlantic affecting climate from New England to western Europe as far
    eastward as central Siberia and eastern Mediterranean and southward to
    West Africa.

    North Pacific High
    A semi-permanent, subtropical area of high pressure in the North Pacific
    Ocean. It is strongest in the Northern Hemispheric summer and is
    displaced towards the equator during the winter when the Aleutian Low
    becomes more dominate. Comparable systems are the Azores High and the
    Bermuda High.

    North Wall
    The north side boundary of the Gulf Stream generally extending northeast
    from Cape Hatteras where the Gulf Stream turns northeast.

    Northern Lights
    Common name for Aurora Borealis; the luminous, radiant emission from the
    upper atmosphere over middle and high latitudes, and centred around the
    earth's magnetic poles. These silent fireworks are often seen on clear
    winter nights in a variety of shapes and colours.

    Nor'easter
    A strong low pressure system that affects the Mid Atlantic and New
    England States. It can form over land or over the coastal waters. These
    winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach
    erosion and structural damage. Wind gusts associated with these storms
    can exceed hurricane force in intensity. A nor'easter gets its name from
    the continuously strong northeasterly winds blowing in from the ocean
    ahead of the storm and over the coastal areas.

    Nowcast
    A short-term weather forecast, generally out to six hours or less. This
    is also called a Short Term Forecast.

    NR
    Near

    NRN
    Northern

    NRW
    Narrow

    NS
    Nimbostratus- 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, usually below 8000 ft (2400 m).

    NSSFC
    National Severe Storm Forecast Center

    NSSL
    National Severe Storms Laboratory - this is one of NOAA's internationally
    known Environmental Research Laboratories, leading the way in
    investigations of all aspects of severe weather. Headquartered in Norman
    OK with staff in Colorado, Nevada, Washington, Utah, and Wisconsin, the
    people of NSSL, in partnership with the National Weather Service, are
    dedicated to improving severe weather warnings and forecasts in order to
    save lives and reduce property damage.

    Numerical Forecasting
    A computer forecast or prediction based on equations governing the
    motions and the forces affecting motion of fluids. The equations are
    based, or initialized, on specified weather or climate conditions at a
    certain place and time.

    Numerical Weather Prediction
    Same as Numerical Forecasting; a computer forecast or prediction based
    on equations governing the motions and the forces affecting motion of
    fluids. The equations are based, or initialized, on specified weather
    or climate conditions at a certain place and time.

    Numerous
    A National Weather Service convective precipitation descriptor for a
    60 or 70 percent chance of measurable precipitation (0.01 inch).

    NVA
    Negative Vorticity Advection - the advection of lower values of vorticity
    into an area.

    NW
    Northwest

    NWD
    Northward

    NWLY
    Northwesterly

    NWP
    Numerical Weather Prediction

    NWR
    NOAA Weather Radio - "the voice of the National Weather Service" - NOAA
    Weather Radio broadcasts National Weather Service warnings, watches,
    forecasts and other hazard information 24 hours a day. It is provided as
    a public service by NOAA. The NOAA Weather Radio network has more than
    480 stations in the 50 states and near adjacent coastal waters, Puerto
    Rico, the U.S. Virgin Islands and U.S. Pacific Territories. It is found
    from 162.40 to 162.55 Megahertz on the Public Service Band.

    NWRD
    Northwestward

    NWRN
    Northwestern

    NWS
    National Weather Service. 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.

    NWSH
    National Weather Service Headquarters

    NWSO
    National Weather Service Office

    NXT
    Next
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