Subj : Wx Terms (G)(2) To : All From : Daryl Stout Date : Sun Oct 08 2017 12:05 am GFS (Global Forecast System) One of the operational forecast models run at NCEP. The GFS is run four times daily, with forecast output out to 384 hours. GIS Geographic Information System. A computer-based graphics program that allows the superposition of plan-maps of thematic elements, such as roads, rivers, land use patterns, and the like to aid in local or regional planning activities. Glaciation The transformation of cloud particles from water drops to ice crystals. Thus, a cumulonimbus cloud is said to have a "glaciated" upper portion. Glacier In hydrologic terms, bodies of land ice that consist of recrystallized snow accumulated on the surface of the ground, and that move slowly downslope. Glacier Dammed Lake In hydrologic terms, the lake formed when a glacier flows across the mouth of an adjoining valley and forms an ice dam. Glacier Wind A shallow downslope wind above the surface of a glacier, caused by the temperature difference between the air in contact with the glacier and the free air at the same altitude. The glacier wind does not reverse diurnally like slope and along-valley wind systems. Glaze Ice formed by freezing precipitation covering the ground or exposed objects. GLF (Open Lakes Forecast) - A National Weather Service marine forecast product for the U.S. waters within a Great Lake not including the waters covered by an existing Nearshore Waters Forecast (NSH). When the seasonal Nearshore forecast is not issued, the Open Lake forecast includes a forecast of nearshore waters. 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. Global Temperature Change The net result of four primary factors including the greenhouse effect, changes in incoming solar radiation, altered patterns of ocean circulations, and changes in continental position, topography and/or vegetation. Three feedback mechanisms which affect global temperature change include cloud height and amount, snow and ice distribution, and atmospheric water vapor levels. Global Warming An overall increase in world temperatures which may be caused by additional heat being trapped by greenhouse gases. Glory An optical effect characterized by concentric rings of color (red outermost and violet innermost) surrounding the shadow of an observer's head when the shadow is cast onto a cloud deck below the observer's elevation (see Brocken specter). GLS (Great Lakes Storm Summary) A National Weather Service forecast product providing updated information whenever a storm warning is in effect on any of the Great Lakes. GMDSS (Global Maritime Distress and Safety System)- The Global Maritime Distress and Safety System (GMDSS) is intended to provide more effective and efficient emergency and safety communications and disseminate Maritime Safety Information (MSI) to all ships on the world's oceans regardless of location or atmospheric conditions. MSI includes navigational warnings, meteorological warnings and forecasts, and other urgent safety related information. GMDSS goals are defined in the International Convention for The Safety Of Life At Sea (SOLAS). The National Weather Service participates directly in the GMDSS by preparing meteorological forecasts and warnings for broadcast via NAVTEX and SafetyNET. GMN On a buoy report, the minute of the hour that the GSP occurred, reported at the last hourly 10-minute segment. GMT Greenwich Mean Time (now known as Universal Coordinated Time). GND Ground GNRL General GOES Geostationary Operational Environmental Satellite- Satellites orbiting at 22,370 miles above the Earth's surface with the same rotational velocity as the Earth; therefore, the satellite remains over the same location on the Earth 24 hours a day. Besides sending back satellite pictures to earth, it also relays the DCPs river and rainfall data back to the ground. GoMoos Gulf Of Maine Ocean Observing System GPS An acronym for Global Positioning System. A network of satellites which provide extremely accurate position and time information. Useful in remote locations or for moving platforms. GRAD Gradient- A rate of change with respect to distance of a variable quantity, as temperature or pressure, in the direction of maximum change. Gradient (abbrev. GRAD) A rate of change with respect to distance of a variable quantity, as temperature or pressure, in the direction of maximum change. Gradient High Winds These high winds usually cover a large area and are due to synoptic-scale, extra-tropical low pressure systems. Gradual Commencement In solar-terrestrial terms, the commencement of a geomagnetic storm that has no well-defined onset. Granulation In solar-terrestrial terms, the cellular structure of the photosphere visible at high spatial resolution. Graupel Same as snow pellets or small hail. Gravity Dam In hydrologic terms, a concrete structure proportioned so that its own weight provides the major resistance to the forces exerted on it. Gravity Wave A wave created by the action of gravity on density variations in the stratified atmosphere. A generic classification for lee waves, mountains waves, and many other waves that form in the atmosphere. Graybody A hypothetical "body" that absorbs some constant fraction of all electromagnetic radiation incident upon it. GRDL Gradual Great Circle Track A great-circle track is the shortest distance between two points on a sphere, and when viewed on a 2-dimensional map the track will appear curved. Swell waves travel along routes that mark out great circles. Great Lakes Faxback Dissemination systems housed at Weather Forecast Office (WFO) Cleveland by which Great Lakes customers request and receive hard copies of selected marine products. Great Lakes Freeze-Up/Break-Up Outlook (FBO) - A National Weather Service product to keep mariners informed of the projected freeze-up date or break-up date of ice on the Great Lakes. Great Lakes Marine Forecast (MAFOR) A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts. Great Lakes Storm Summary (GLS) - A National Weather Service forecast product providing updated information whenever a storm warning is in effect on any of the Great Lakes. Great Lakes Weather Broadcast (LAWEB) - A National Weather Service product containing an observation summary prepared to provide Great Lakes mariners with a listing of weather observations along or on the Lakes. Green Line The green line is one of the strongest (and first-recognized) visible coronal lines. It identifies moderate temperature regions of the CORONA. Greenhouse Effect Atmospheric heating caused by solar radiation being readily transmitted inward through the earth's atmosphere but longwave radiation less readily transmitted outward, due to absorption by certain gases in the atmosphere. Greenhouse Gases The gases that absorb terrestrial radiation and contribute to the greenhouse effect; the main greenhouse gasses are water vapor, methane, carbon dioxide, and ozone. GRIB (Gridded Binary Format) - A format used for meteorological data. Typically used in the past for computer generated model data but will be used increasingly in the future for forecaster generated data. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .