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 American 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 Blend of Models (NBM)

The National Blend of Models (NBM) is a nationally consistent and skillful suite of calibrated forecast guidance based on a blend of both NWS and non-NWS numerical weather prediction model data and post-processed model guidance.

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 Hydrologic Discussion (NHD)

A discussion of the current and forecast hydrologic conditions across the nation, including a variety of short and medium range (Days 1-10) observed and modeled hydrologic guidance.

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 Water Model (NWM)

A hydrologic modelling framework that simulates observed and forecast streamflow over the entire continental United States and Hawaii.

National Water Model Medium-Range Forecast (NWM MRF)

A 10-day streamflow forecast for the over 3.6 million waterway miles across the Nation, forced by the GFS and updated every 6 hours.

National Water Model Short-Range Forecast (NWM SRF)

An 18-hour streamflow forecast for the over 3.4 million waterway miles across the Nation, forced by the HRRR and updated hourly.

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 areas 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 ~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 it’s 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.

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 American Ensemble Forecast System (NAEFS)

An atmospheric ensemble of 20 members each from the NCEP GEFS and CMC EPS ensemble systems.

North American Mesoscale Forecast System (NAM)

One of the major weather models run by the National Centers for Environmental Prediction (NCEP) for producing weather forecasts.

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.

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

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