Subj : Weather Glossary (G)
To : All
From : Daryl Stout
Date : Fri Mar 08 2019 10:55 am
This weather glossary contains information on more than 2000 terms,
phrases and abbreviations used by the National Weather Service (NWS)...
the government agency who makes weather forecasts, and issues weather
advisories, watches, and warnings, for the United States, and its
territories.
Many of these terms and abbreviations are used by NWS forecasters to
communicate between each other and have been in use for many years and
before many NWS products were directly available to the public. It is the
purpose of this glossary to aid you in better understanding NWS products.
***
G
Gusts- A rapid fluctuation of wind speed with variations of 10 knots or
more between peaks and lulls.
G/KG
Grams per Kilogram
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
A horizontal surface used as a zero point for measurement of stage or
gage height. This surface usually is located slightly below the lowest
point of the stream bottom such that the gage height is usually slightly
greater than the maximum depth of water. Because the gage datum is not
an actual physical object, the datum is usually defined by specifying
the elevations of permanent reference marks such as bridge abutments
and survey monuments, and the gage is set to agree with the reference
marks. Gage datum is a local datum that is maintained independently of
any national geodetic datum. However, if the elevation of the gage datum
relative to the national datum (North American Vertical Datum of 1988
or National Geodetic Vertical Datum of 1929) has been determined, then
the gage readings can be converted to elevations above the national
datum by adding the elevation of the gage datum to the gage reading.
Gaging Station
In hydrologic terms, a particular site on a watercourse where systematic
observations of stage/ and or flow are measured.
Gale
An extratropical low or an area of sustained surface winds of 34 (39 mph)
to 47 knots (54 mph).
Gale Warning
A warning of sustained surface winds, or frequent gusts, in the range of
34 knots (39 mph) to 47 knots (54 mph) inclusive, either predicted or
occurring, and not directly associated with a tropical cyclone.
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 horizontal
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
(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.
Grids
1) Squared off areas across the terrain used to define forecast areas.
Often 5x5 or 2.5x2.5 kilometer in size.
2) Digitial forecast databases for meteorological elements, including
temperature, wind direction, wind speed and others. Computer programs
read these databases to create worded and graphical forecast products
used by the public and others.
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. Also known as "anomalous propagation".
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.
Growler
Similar to a bergy bit, but smaller, extending less than 1 meter above
the sea surface and occupying an area of 20 square meters or less.
GRT
great
GRTST
Greatest
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
Warm water current extending from the Gulf of Mexico and Florida up the
U.S. east coast then east northeast to Iceland and Norway.
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.
Gyres
Oceanic current systems of planetary scale driven by the global wind
system.
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