Subj : Wx Terms (N)(1) To : All From : Daryl Stout Date : Sat Jul 15 2017 12:06 am 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 --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .