Weather Glossary


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G Gusts- A rapid fluctuation of wind speed with variations of 10 knots or more between peaks and lulls.
Gage In hydrologic terms,
1) A device for indicating the magnitude or position of a thing in specific units, when such magnitude or position undergoes change, for example: The elevation of a water surface, the velocity of flowing water, the pressure of water, the amount or intensity of precipitation, the depth of snowfall, etc.
(2) The act or operation of registering or measuring the magnitude or position of a thing when these characteristics are undergoing change.
(3) The operation, including both field and office work, of measuring the discharge of a stream of water in a waterway.
Gage Datum In hydrologic terms, the arbitrary zero datum elevation which all stage measurements are made from
Gaging Station In hydrologic terms, a particular site on a watercourse where systematic observations of stage/ and or flow are measured.
Gale Wind speeds from 39 to 54 mph (34 to 47 knots).
Gale Warning The National Weather Service will issue these marine warnings for 1-minute sustained winds between 34 (39 mph or 63 kph) and 47 knots (54 mph or 87 kph) are expected at end of downwind fetch (nearshore or open waters).
Gallery In hydrologic terms, a passageway within the body of a dam or abutment.
Gamma A unit of magnetic field intensity equal to 1 x 10.0-5 Gauss; also equal to 1 nanotelsa (nT).
Gamma Ray A type of electromagnetic radiation with a very short wavelength and high energy level. Generally, emitted during radioactive decay of a substance.
Gap Winds Strong winds channeled through gaps in the Pacific coastal ranges, blowing out into the Pacific Ocean or into the waterways of the Inside Passage. The winds blow through low passes where major river valleys issue onto the seaways when strong east-west pressure gradients exist between the coast and the inland areas, with low pressure over the ocean.
Gas Laws The thermodynamic laws pertaining to perfect gases, including Boyle's law, Charles' law, Dalton's law and the equation of state.
Gate In hydrologic terms, a device in which a leaf or member is moved across the waterway from an external position to control or stop flow. There are many different kinds of gates used on a dam
Gauss The unit of magnetic induction in the cgs (centimeter-gram- second) system
Gaussian Plume Model A computer model used to calculate air pollution concentrations. The model assumes that a pollutant plume is carried downwind from its emission source by a mean wind and that concentrations in the plume can be approximated by assuming that the highest concentrations occur on the horizontal and vertical midlines of the plume, with the distribution about these mid-lines characterized by Gaussian- or bell-shaped concentration profiles.
Gaussian Puff Model A model used to calculate air pollution concentrations. The model assumes that a continuously emitted plume or instantaneous cloud of pollutants can be simulated by the release of a series of puffs that will be carried in a time- and space-varying wind field. The puffs are assumed to have Gaussian or bell-shaped concentration profiles in their vertical and horizontal planes.
GDR On a buoy report, direction, in degrees clockwise from true North, of the GSP, reported at the last hourly 10-minute segment.
GEMPAK General Environmental Meteorological Package (programming language)
GEN General
General Circulation The totality of large-scale organized motion for the entire global atmosphere.
General Circulation Models (GCMs) - These computer simulations reproduce the Earth's weather patterns and can be used to predict change in the weather and climate.
General Wind Land management agency term for winds produced by synoptic-scale pressure systems on which smaller-scale or local convective winds are superimposed.
Geohydrology In hydrologic terms, the branch of hydrology relating to subsurface, or subterranean waters.
Geomagnetic Elements In solar-terrestrial terms, the components of the geomagnetic field at the surface of the earth. In SESC use, the northward and eastward components are often called the H and D components, where the D component is expressed in gammas and is derived from D (the declination angle) using the small angle approximation.
Geomagnetic Field The magnetic field observed in and around the earth. The intensity of the magnetic field at the earth's surface is approximately 0.32 gauss at the equator and 0.62 gauss at the north pole
Geomagnetic Storm In solar-terrestraial terms, a worldwide disturbance of the earth's magnetic field, distinct from regular diurnal variations.
Minor Geomagnetic Storm: A storm for which the Ap index was greater than 29 and less than 50.
Major Geomagnetic Storm: A storm for which the Ap index was greater than 49 and less than 100.
Severe Geomagnetic Storm: A storm for which the Ap index was 100 or more.
Initial Phase: Of a geomagnetic storm, that period when there may be an increase of the middle-latitude horizontal intensity (H).
Main Phase: Of a geomagnetic storm, that period when the hori- zontal magnetic field at middle latitudes is generally decreasing.
Recovery Phase: Of a geomagnetic storm, that period when the depressed northward field component returns to normal levels.
Geophysical Events In solar-terrestrial terms, flares (Importance two or larger) with Centimetric Outbursts (maximum of the flux higher than the Quiet Sun flux, duration longer 10 minutes) and/or strong SID. Sometimes these flares are followed by Geomagnetic Storms or small PCA. (Class M Flares)
Geophysics In hydrologic terms, the study of the physical characteristics and properties of the earth; including geodesy, seismology, meteorology, oceanography, atmospheric electricity, terrestrial magnetism, and tidal phenomena.
Geopotential Height The height above sea level of a pressure level. For example, if a station reports that the 500 mb height at its location is 5600 m, it means that the level of the atmosphere over that station at which the atmospheric pressure is 500 mb is 5600 meters above sea level. This is an estimated height based on temperature and pressure data.
Geostationary Satellite A satellite that rotates at the same rate as the earth, remaining over the same spot above the equator.
Geostrophic Wind A wind that is affected by coriolis force, blows parallel to isobars and whose strength is related to the pressure gradient (i.e., spacing of the isobars).
Geosynchronous Term applied to any equatorial satellite with an orbital velocity equal to the rotational velocity of the earth. The net effect is that the satellite is virtually motionless with respect to an observer on the ground
GF Ground Fog- Fog produced over the land by the cooling of the lower atmosphere as it comes in contact with the ground. Also known as radiation fog, and in parts of California as tule fog.
GFS The Global Forecast System (360-hour numerical model of the atmosphere). Previously known as the AVN and MRF.
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.
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).
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
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
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.
Ground Blizzard Warning When blizzard conditions are solely caused by blowing and drifting snow.
Ground Clutter A pattern of radar echoes from fixed ground targets (buildings, hills, etc.) near the radar. Ground clutter may hide or confuse precipitation echoes near the radar antenna.
Ground Fog (abbrev. GF) Fog produced over the land by the cooling of the lower atmosphere as it comes in contact with the ground. Also known as radiation fog, and in parts of California as tule fog.
Ground Heat Flux The flux of heat from the ground to the earth's surface; a component of the surface energy budget.
Ground receive sites In hydrologic terms, a satellite dish and associated computer which receives signals from the GOES satellite, decodes the information, and transmits it to a another site for further processing. The GOES satellite ground-receive site is located at Wallops Island, VA; and the information is relayed to a mainframe computer at NWSH for processing.
Ground Stroke The current that propagates along the ground from the point where a direct stroke of lightning hits the ground.
Ground Water In hydrologic terms, water within the earth that supplies wells and springs; water in the zone of saturation where all openings in rocks and soil are filled, the upper surface of which forms the water table. Also termed Phreatic water.
Ground Water Divide In hydrologic terms, A line on a water table where on either side of which the water table slopes downward. It is analogous to a drainage divide between two drainage basins on a land surface
Ground Water Flow In hydrologic terms, streamflow which results from precipitation that infiltrates into the soil and eventually moves through the soil to the stream channel. This is also referred to as baseflow, or dry-weather flow
Ground Water Hydrology The branch of hydrology that specializes in ground water; its occurrence and movements; its replenishment and depletion; the properties of rocks that control ground water movement and storage; and the methods of investigation and utilization of ground water
Ground Water Outflow In hydrologic terms, the part of the discharge from a drainage basin that occurs through the ground water. The term "underflow" is often used to describe the ground water outflow that takes place in valley alluvium (instead of the surface channel) and thus is not measure at a gaging station.
Ground Water Overdraft Pumpage of ground water in excess of safe yield.
Ground Water Runoff That part of the runoff which has passed into the ground, has become ground water, and has been discharged into a stream channel as spring, or seepage water.
Grounded ice In hydrologic terms, ice that has run aground or is contact with the ground underneath it
Group Velocity The speed at which a particular wave front or swell train advances.
Grout Curtain A barrier produced by injecting grout into a vertical zone, usually narrow (horizontally), and in the foundation to reduce seepage under a dam
Growing Degree Day The number of degrees that the average temperature is above a baseline value. For example, 40 degrees for canning purposes; 45 degree for potatoes; and 50 degrees for sweet corn, snap beans, lima beans, tomatoes, grapes, and field corn. Every degree that the average temperature is above the baseline value becomes a growing degree day. Agricultural related interests use growing degree days to determine planting times.
Growing Season the period of time between the last killing frost of spring and the first killing frost of autumn.
GRT great
GSP On a buoy report, maximum 5-second peak gust during the measurement hour, reported at the last hourly 10-minute segment.
GST On a buoy report, peak 5 or 8 second gust speed (m/s) measured during the eight-minute or two-minute period. The 5 or 8 second period can be determined by payload.
GSTY Gusty
GTR Greater
Gulf Stream A warm, swift, relatively narrow ocean current that flows along the east coast of the United States.
Gunge Slang for anything in the atmosphere that restricts visibility for storm spotting, such as fog, haze, precipitation (steady rain or drizzle), widespread low clouds (stratus), etc.
Gust (Abbrev. G) - A rapid fluctuation of wind speed with variations of 10 knots or more between peaks and lulls.
Gust Front The leading edge of gusty surface winds from thunderstorm downdrafts; sometimes associated with a shelf cloud or roll cloud. See also gustnado or outflow boundary.
Gustnado (or Gustinado) - [Slang], gust front tornado. A small tornado, usually weak and short-lived, that occurs along the gust front of a thunderstorm. Often it is visible only as a debris cloud or dust whirl near the ground. Gustnadoes are not associated with storm-scale rotation (i.e. mesocyclones); they are more likely to be associated visually with a shelf cloud than with a wall cloud.