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G

Gage:  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 The arbitrary zero datum elevation which all stage measurements are made from.
 
Gage Height:  The water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term stage, although gage height is more appropriate when used with a reading on a gage.
 
Gage Zero:  The elevation of zero stage. (Same as gage datum.)
 
Gaging Station: A particular site on a river, stream, canal, or body of water where systematic observations of stage and/or flow are measured.

Gain:  A change in signal power, voltage or current. Usually applied to a change greater than one and frequently expressed in decibels.

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).  This warning will be headlined in the Open Great Lakes Forecast (Product Header CCCGLFXX) and the Nearshore Marine Forecast (Product Header CCCNSHXXX) when conditions are expected to occur within 24 hours following the forecast issuance time.  The headline will be "...GALE WARNING IN EFFECT...".  When the hazard has ended, the last forecast will indicate this in the headline by replacing the "IN EFFECT" phrase with "DISCONTINUED".

Gallery:  A passageway within the body of a dam or abutment.

Gate:  1) 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. Some include:   Bulkhead, Crest (or Spillway), Emergency, Fixed Wheel, Flap, Flood, Guard, Outlet, Radial, Regulating, and Slide Gates. 2) A radar term see Range Gate.

Gating (Range Gating):  The use of electric circuits in radar to eliminate or discard the target signals from all targets falling outside certain desired range limits.

GaussianRefers to the normal distribution; phenomena whose events are "normally" distributed are "Gaussian" distributed. This is the most common distribution encountered in physical processes.

Geohydrology:  That branch of hydrology relating to subsurface, or subterranean waters.
 
Geophysics:  The study of the physical characteristics and properties of the earth; including geodesy, seismology, meteorology, oceanography, atmospheric electricity, terrestrial magnetism, and tidal phenomena.
 
Geostrophic Wind: The horizontal wind for which the coriolis acceleration (caused by the Earth's rotation) exactly balances the horizontal pressure force. In practice it is assumed that this marks the upper limit of frictional influence of the Earth's surface. The geostrophic wind blows along the contours on a constant pressure surface. The speed of the geostrophic wind is dependent upon how close your pressure contour are together. Thus, when your pressure contours are close together, you will see a strong geostrophic wind. The opposite occurs when your pressure contours are far apart.

Glacier:  Bodies of land ice that consist of recrystallized snow accumulated on the surface of the ground, and that move slowly downslope.
 
Glacier Dammed Lake:  The lake formed when a glacier flows across the mouth of an adjoining valley and forms an ice dam.
 
Glaze: Ice formed by freezing precipitation covering the ground or exposed objects.

Global Maritime Distress and Safety System (GMDSS):  An internationally agreed upon communication system for distributing safety information, including weather warnings and forecasts, to mariners.

Global Ocean Model:  Another global model used by NCEP is the Global Ocean Model. The ocean model forecasts seasonal changes in oceanic variables, such as sea surface temperature and ocean currents. The ocean model is coupled with an atmospheric model to help determine how forecasted changes in oceanic variables, such as sea surface temperature, will affect the atmosphere. This model tandem is not used to give detailed daily forecasts for the ocean or the atmosphere like some of the other models.  Instead it is mainly used to help forecast seasonal or yearly variations of the ocean and the atmosphere. The ocean model coupled with the atmospheric model is used to forecast events such as an El Nino warming event in the Pacific Ocean and in long range seasonal outlooks.

Global Warming: An overall increase in world temperatures which may be caused by additional heat being trapped by greenhouse gases.

GOES (Geostationary Orbiting 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 receiving located at Wallops Island, Virginia.

GOES DCS (Data Collection System):  A data collection system under NESDIS which is comprised of the DCPs, and the NESDIS Command and Data Acquisition (CDA) System components. This satellite-based system collects a variety of environmental data from locations in the Western Hemisphere. The system is a data relay network for more than 10,000 DCPs which transmits data to one of two GOES satellites (East and West). These data are relayed to the NESDIS CDA ground station located at Wallops Island, VA. The data are then relayed over to Silver Springs, MD, where the data is then distributed to the appropriate recipients.

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.

Graupel:  A lightly rimed ice aggregate often found in vigorous storms. Formed when an ice aggregate collects supercooled liquid water droplets.

Gravity Dam:  A concrete structure proportioned so that its own weight provides the major resistance to the forces exerted on it.

Great Lakes 5-Day Ice Outlook (Product Header CLEICELIO):  This ice outlook is issued by NWFO Cleveland, Ohio daily at about 3:30 PM local time.  It includes sections on expected synoptic weather patterns and temperatures for 5 days, expected winds for 3 periods (about 36 hours) and effect of those parameters on ice formation or decay, and other changes affecting navigation.  Additional information, such as normal temperatures, the accumulated freezing degree days, and observed ice thicknesses will be included in this product.

Great Lakes Freeze-Up Outlook (Product Header CLEICEFBO):  The freeze-up outlook is issued by NWFO Cleveland, Ohio in the fall around November 1st.  It indicates whether ice conditions will occur earlier, later, or about the normal times over the lakes.  Supporting data, such as selected water temperatures from water intakes and NOAA data buoys, will also be provided in this product.

Great Lakes Ice Outlook for the Opening of Navigation (Product Header CLEICEFBO):  This outlook is issued by NWFO Cleveland, Ohio in the spring around March 1st.  It gives a summary of current ice thickness and a listing of dates when shipping is expected to be able to navigate an area without icebreaker assistance.

Great Lakes Marine Synopsis (Product Header CLEGLFGLS):  This product is prepared by NWFO Cleveland, Ohio.  It summarizes the forecast positions and movements of highs, lows, and fronts affecting the Great Lakes for the 24-hour period beginning at the synoptic time after its issuance.  The synopsis will also give the strength of high and low pressure systems in inches of mercury.  At the end of the synopsis, there will be a 12-hour outlook.  All references to time in the product will be given in Eastern Standard Time (EST) throughout the year.

Great Lakes Storm Outlook (Product Header CLEGLOCLE):  This unscheduled product is issued by NWFO Cleveland, Ohio to alert users to potentially dangerous conditions from continuous storm force winds (greater than 48 knots) over one or more of the Great Lakes within a 36- to 48-hour periods after its issuance.  The outlook is based on NMC guidance and does not replace any other product.
The outlook will describe where and when the storm force winds may occur, give a brief description of the synoptic weather patterns that would cause such winds, and provide a brief call-to-action statements regarding further information.

Great Lakes Storm Summary (Product Header CLEGLSCLE) These summaries will be issued by NWFO Cleveland, Ohio as soon as sustained winds of 50 knots or more are produced by any synoptic scale storm when such winds are expected to continue on any of the Great Lakes for 12 hours or more.  Summaries are numbered consecutively following the media header.  The summary will include the following information: 1) storm location, 2) storm movement, 3) highest reported winds, 4) storm intensity trend, 5) current marine warnings in effect, 6) additional information will be included in the Remark Section of the summary, and 7) when the next advisory will be issued by NWFO Cleveland, Ohio.  These summaries will normally be issued every 3 hours after the first issuance.

Greenhouse Effect: The heating effect caused by gases in the atmosphere absorbing heat (solar radiation) instead of letting it escape back into space. There are 2 types: 1) Natural: It is what keeps the Earth's average temperature at 59oF instead of 0oF. In this case, the most abundant greenhouse gas is water vapor. 2) Anthropogenic: Additional warming caused by having too much carbon dioxide (CO2). In the first case, the Greenhouse Effect is good; however, if the second case is occurring it will be bad.

Ground Blizzard Warning:  When blizzard conditions are solely caused by blowing and drifting snow.

Ground ClutterA 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.  It is usually more noticeable at night when the radar beam is encountering superrefractive conditions.

Ground Fog: Fog of little vertical extent (usually 20 feet or less).

Grounded Ice:  Ice that has run aground or is contact with the ground underneath it.

Ground Receiver Site:  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 Water:  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:  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 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 Mining:  Pumping ground water from a basin where the safe yield is very small, thereby extracting ground water which had accumulated over a long period of time.
 
Ground Water Outflow:  That 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:  The part of runoff, caused by precipitation and/or snowmelt, that passes into the ground, becomes ground water, and gets discharged into a stream or river as spring or seepage water.

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 Days: 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.

Gulf Stream: A warm, swift, narrow ocean current flowing 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:  A rapid fluctuation of wind speed with variations of 10 knots or more between peaks and lulls.

Gust Front: Formed when the down draft and rain-cooled air of a thunderstorm reach the ground, and then spread out along the ground. Usually marked by a sudden wind shift, sharply falling temperatures, and possibly heavy downpours and/or hail. If two or more of these gust fronts intersect each other, a new thunderstorm could possibly develop.  Sometimes it is associated with a shelf cloud or roll cloud.  Also, see downburst, gustnado, and outflow boundary

GustnadoSlang for a 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.

Gyre:  A circular or spiral motion, primarily referring to water currents.

GyroA device used for measuring changes in direction. Often used in antenna stabilization.  


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