NADIR
The point on any given observer's celestial sphere diametrically opposite of one's zenith.
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.
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.
NCMRWF
National Council of Medium Rage Weather Forecast- an institution set up under the Department of Science & Technology of Government of India. It provides weather forecasts through deterministic methods and to render Agro Advisory Services (AAS) to the farmers. The centre offers challenging research opportunities in Numerical Weather Prediction, Diagnostic studies, Crop Weather Modeling and Computer Science.
Web Site :- http://www.ncmrwf.gov.in
NEAP TIDE
A tide of decreased range, which occurs about every two weeks when the moon is at one quarter or three-quarters full.
NEGATIVE VORTICITY ADVECTION
The advection of lower values of vorticity into an area.
NEPHELOCOCCYGIA
A term applied when people find familiar objects within the shape of a cloud.
NEWTON
The unit of force giving a mass of about one kilogram (2.205 pounds) an acceleration of about one meter (1 yard) per second per second.
NIGHT
The period of the day between dusk and dawn.
NIMBOSTRATUS
This cloud exhibits a combination of rain or snow, and sometimes the base of the cloud cannot be seen because of the heaviness of precipitation. They are generally associated with fall and winter conditions, but can occur during any season.
NITROGEN (N2)
A colorless, tasteless, odorless gas that is the most abundant constituent of dry air. It comprises 78.09%.
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.
NOR'EASTER
A cyclonic storm occurring off the east coast of North America. 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.
NORMAL
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.
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.
NOWCAST
A short-term weather forecast for expected conditions in the next few hours.
NUMERICAL FORECASTING
The use of numerical models, such as the fundamental equations of hydrodynamics subjected to observed initial conditions, to forecast the weather.