Along-slope Wind System
A closed, thermally driven diurnal mountain wind circulation whose lower branch blows up or down the sloping sidewalls of a valley or mountain. The upper branch blows in the opposite direction, thereby closing the circulation.
Arch Filament System (AFS)
In solar-terrestrial terms, a bright, compact plage crossed by a system of small, arched filaments, which is often a sign of rapid or continued growth in an Active Region.
Area Wide Hydrologic Prediction System
(Abbrev. AWHPS) - A computer system which automatically ingests areal flash flood guidance values and WSR-88D products and displays this data and other hydrologic information on a map background.
Automated Surface Observing System
The ASOS program is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DOD). Completed in the mid-1990s, the ASOS systems serve as the nation's primary surface weather observing network. ASOS is designed to support weather forecast activities and aviation operations and, at the same time, support the needs of the meteorological, hydrological, and climatological research communities.
Barotropic System
A weather system in which temperature and pressure surfaces are coincident, i.e., temperature is uniform (no temperature gradient) on a constant pressure surface. Barotropic systems are characterized by a lack of wind shear, and thus are generally unfavorable areas for severe thunderstorm development. See baroclinic zone.

Usually, in operational meteorology, references to barotropic systems refer to equivalent barotropic systems - systems in which temperature gradients exist, but are parallel to height gradients on a constant pressure surface. In such systems, height contours and isotherms are parallel everywhere, and winds do not change direction with height.

As a rule, a true equivalent barotropic system can never be achieved in the real atmosphere. While some systems (such as closed lows or cutoff lows) may reach a state that is close to equivalent barotropic, the term barotropic system usually is used in a relative sense to describe systems that are really only close to being equivalent barotropic, i.e., isotherms and height contours are nearly parallel everywhere and directional wind shear is weak.
Climate System
The system consisting of the atmosphere (gases), hydrosphere (water), lithosphere (solid rocky part of the Earth), and biosphere (living) that determine the Earth's climate.
Cross-Valley Wind System
A thermally driven wind that blows during daytime across the axis of a valley toward the heated sidewall.
Global Ensemble Forecast System (GEFS)
A weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which are used to initialize weather forecast models.
Global Forecast System
(GFS)- One of the operational forecast models run at NCEP. The GFS is run four times daily, with forecast output out to 384 hours.
Hydrologic Ensemble Forecast System (HEFS)
A probabilistic forecast tool with the goals to provide hydrologic forecasts including an analysis of “probable outcomes” and to minimize biases in the atmospheric models and in the hydrologic models.
Lentic System
In hydrologic terms, a nonflowing or standing body of fresh water, such as a lake or pond
Loop Prominence System
(abbrev. LPS) In solar-terrestrial terms, a system of loop prominences associated with major flares.
Lotic System
In hydrologic terms, a flowing body of fresh water, such as a river or stream.
Low Pressure System
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone.
Mesoscale Convective System
(MCS): A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others). MCS often is used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC.
Mountain Wind System
The system of diurnal winds that forms in a complex terrain area, consisting of mountain-plain, along-valley, cross-valley and slope wind systems.
Mountain-Plain Wind System
A closed, large-scale, thermally driven circulation between the mountains and the surrounding plain. The mountain-to-plain flow making up the lower branch of the closed circulation usually occurs during nighttime, while the plain-to-mountain flow occurs during daytime.
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.
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.
Precipitation Processing System
The WSR-88D system that generates 1-hour running, 3-hourly, and running storm total precipitation accumulations. Five functional steps are performed to calculate the best estimate of precipitation: 1) development of a sectorized hybrid scan, 2) conversion to precipitation rate, 3) precipitation accumulation, 4) adjustment using rain gages, 5) product update.
Remote Observing System Automation
A type of automated data transmitter used by NWS Cooperative Program observers.
River System
In hydrologic terms, all of the streams and channels draining a river basin.
Short-Term Prediction Research and Transition Center - Land Information System (SPoRT-LIS)
Provides high-resolution (~3 km) gridded soil moisture products in real-time to support regional and local modeling and improve situational awareness.
Snow Data Assimilation System (SNODAS)
A physically based, mass conserving snow water equivalent (SWE) model.
Upper Level System
A general term for any large-scale or mesoscale disturbance capable of producing upward motion (lift) in the middle or upper parts of the atmosphere. This term sometimes is used interchangeably with impulse or shortwave.
Vertically Stacked System
A low-pressure system, usually a closed low or cutoff low, which is not tilted with height, i.e., located similarly at all levels of the atmosphere. Such systems typically are weakening and are slow-moving, and are less likely to produce severe weather than tilted systems. However, cold pools aloft associated with vertically-stacked systems may enhance instability enough to produce severe weather.
WSR-88D System
The summation of all hardware, software, facilities, communications, logistics, staffing, training, operations, and procedures specifically associated with the collection, processing, analysis, dissemination and application of data from the WSR-88D unit.

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