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NOAA - Meteorology glossary
Category: Sciences > Meteorology
Date & country: 14/10/2013, US
Words: 358


Ablation
The process of being removed. Snow ablation usually refers to removal by melting

Absolute Humidity
The density of water vapor. It is the mass of the water vapor divided by the volume that it occupies.

Accretion
Growth of precipitation particles by collision of ice crystals with supercooled liquid droplets which freeze on impact

Adiabatic
changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or descends in the atmosphere.

Advection Fog
a type of fog that results from the advection of moist air over a cold surface and the cooling of the air to its dew point that follows; this type of fog is most common in coastal regions.

Aerovane
Aerovanes are commonly used at many weather stations and airports to measure both wind direction and speed. They are similar to wind vanes and cup anemometers except have three-bladed propellers attached to the end of the vane.

AGL
above ground level.

Air
the mixture of gases that make-up the earth's atmosphere.

Air Mass
A large body of air that has similar horizontal temperature and moisture characteristics.

Air Pressure
(atmospheric pressure) air pressure is the force exerted on a surface by the weight of the air above it. The internationally recognized unit for measuring this pressure is the kilopascal.

Airstream
A significant body of air flowing in the same general circulation.

Albedo
The percentage of light reflected by an object. Snow covered areas have a high albedo (0.9 or 90%) due to their white color.

Altimeter
An active instrument (see active system) used to measure the altitude of an object above a fixed level.

Altimeter setting
That pressure value to which an aircraft altimeter scale is set so that it will indicate the altitude above mean sea-level of an aircraft on the ground at the location for which the value was determined.

Altocumulus
Mid-altitude clouds with a cumuliform shape.

Altostratus
Mid-altitude clouds with a flat sheet-like shape.

Anafront
A front at which the warm is ascending the frontal surface up to high altitudes.

Anemometer
An instrument that measures wind speed.

Aneroid barometer
An instrument built around a metal structure that bends with changing air pressure. These changes are recorded on a pointer that moves back and forth across a printed scale.

Angular Momentum
the energy of motion of a spinning body or mass of air or water.

Angular Velocity
the rate at which a spinning body rotates.

Anomaly
The deviation of (usually) temperature or precipitation in a given region over a specified period from the normal value for the same region.

Anticyclone
A large body of air in which the atmospheric pressure is higher than the pressure in the surrounding air. The winds blow clockwise around an anticyclone in in the Northern Hemisphere.

Anvil Dome
A large overshooting top or penetrating top.

Arctic High
a very cold high pressure that originates over the Arctic Ocean.

Atmosphere
The mass of air surrounding the earth and bound to it more or less permanently by the earth's gravitational attraction.

Atmospheric Pressure
(also called air pressure or barometric pressure) The pressure asserted by the mass of the column of air directly above any specific point.

Atmospheric Stability
An indication of how easily a parcel of air is lifted. If the air is very stable it is difficult to make the parcel rise. If the air is very unstable the parcel may rise on its own once started.

Aurora Borealis
Also known as the northern lights

Automated Weather Station
An unmanned station with various sensors that measure weather elements such as temperature/wind/pressure and transmit these readings for use by meteorologists.

Avalanche
a large mass of rapidly moving snow down a steep mountain slope.

AVN
Aviation Model generated every 12 hours by NCEP.

Baroclinic Zone
A region in which a temperature gradient exists on a constant pressure surface. Baroclinic zones are favored areas for strengthening and weakening systems.

Barogram
The graphic record of pressure produced by a barograph.

Barograph
An instrument that provides a continuous record of atmospheric pressure.

Barometer
An instrument for measuring atmospheric pressure.

Barometric pressure
The actual pressure value indicated by a pressure sensor.

Barometric Tendency
The amount and direction of change in barometer readings over a three-hour period.

Beaufort Scale
A scale that indicates the wind speed using the effect wind has on certain familiar objects.

Blizzard warning
Issued when blizzard condition are expected or are occurring.

Blowing Dust
dust that is raised by the wind to moderate heights above the ground to a degree that horizontal visibility decreases to less than seven miles. Visibilities of 1/8 mile or less over a widespread area are criteria for a Blowing Dust Advisory.

Blowing Snow
Wind driven snow that reduces visibility to six miles or less causing significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind.

Blustery
Descriptive term for gusty winds that accompany cold weather.

Bomb Cyclone
An extratropical area of low pressure in which the central pressure drops at least 24 millibars in 24 hours.

Box (or Watch Box)
A severe thunderstorm or tornado watch.

Breezy
Wind in the range of 15 mph to 25 mph with mild or warm temperatures.

Brisk
Wind in the range of 15 to 25 mph when the temperature is cold.

Broken Clouds
Clouds which cover between 5/8ths and 7/8ths of the sky.

CAA
Cold Air Advection

Calm
the absence of apparent motion in the air.

Cb
Cumulonimbus cloud

Ceiling
The height of the lowest layer of broken or overcast clouds.

Ceilometer
A device used to evaluate the height of clouds or the vertical visibility into a surface-based obscuration.

Celsius
a temperature scale in which zero is the freezing point of water and one hundred is the boiling point.

Chinook Wind
A strong downslope wind that causes the air to warm rapidly as a result of compressive heating; called a foehn wind in Europe.

Cirriform
High altitude ice clouds with a very thin wispy appearance.

Cirrocumulus
Cirrus clouds with vertical development.

Cirrostratus
Cirrus clouds with a flat sheetlike appearance.

Clear
Sky condition of less than 1/10 cloud coverage.

Climatology
the scientific study of climate.

Cloud
A visible cluster of tiny water and/or ice particles in the atmosphere.

Cloud Condensation Nuclei
small particles in the air on which water vapor condenses and forms cloud droplets.

Cloudy
the state of the sky when 7/10ths or more of the sky is covered by clouds.

Coastal Flooding
The inundation of land areas along the coast caused by sea water above normal tidal actions. This is often caused by prolonged strong onshore flow of wind and/or high astronomical tides.

Cold Advection
(CAA) Transport of cold air into a region by horizontal winds.

Cold Air Damming
Cold air damming occurs when a cold dome of high pressure settles over northeastern New England. The clockwise circulation around the high pressure center brings northeasterly winds to the mid Atlantic region. The northeasterly winds bank cold air against the eastern slopes of the Appalachian Mountains. Warmer air from the west or southwest is lifted above the cold air as it moves instead of warming the surface.

Cold Front
A narrow transition zone separating advancing colder air from retreating warmer air. The air behind a cold front is cooler and typically drier than the air it is replacing.

Cold Low
a low pressure system with cold air mass from near the surface to all vertical levels (also called a cold core low).

Combined Seas
The combined height of swell and wind waves.

Condensation Nuclei
Small particles in the air around which water vapor condenses.

Conduction
The transfer of heat by molecular action between bodies that are in contact.

Continental Air Mass
A dry air mass originating over a large land area.

Cooling Degree Day
A form of degree day used to estimate the required energy for cooling. one cooling degree day occurs for each degree the daily mean temperature is above 65 degrees Fahrenheit.

Coordinated Universal Time (UTC)
The time in the zero degree meridian time zone.

Corona
a disk of light surrounding the sun or moon; this is a result of the diffraction of light by small water droplets.

CRS
Console Replacement System. This consists of a computer system and computer voice that is used to automate NOAA Weather Radio.

Cut Off Low
An upper level low pressure system that is no longer in the normal west to east upper air flow. Usually a cut-off low will lie to the South of the established upper air flow.

Cyclogenesis
Development or intensification of a low-pressure center

Cyclone
An area of low pressure around which winds blow counterclockwise in the Northern Hemisphere. Also the term used for a hurricane in the Indian Ocean and in the Western Pacific Ocean.

Decouple
The tendency for the surface wind to become much lighter than wind above it at night when the surface temperature cools.

Degree Day
a measure of the departure of the daily mean temperature from the normal daily temperature; heating and cooling Degree Days are the departure of the daily mean temperature from sixty-five degrees Fahrenheit.

Dendrite
hexagonal ice crystals with complex and often fernlike branches.

Dense Fog
a fog in which the visibility is less than one-quarter mile.

Dense Fog Advisory
Issued when fog is expected to reduce visibility to 1/4 mile or less over a widespread are for at least 3 hours.

Density Altitude
The pressure altitude corrected for temperature deviations from the standard atmosphere. It is used by pilots when setting aircraft performance.

Depression
a region of low atmospheric pressure that is usually accompanied by low clouds and precipitation.

Dew Point
The temperature to which the air must be cooled for water vapor to condense and form fog or clouds.

Divergence
The expansion or spreading out of a vector field; usually said of horizontal winds. It is the opposite of convergence.

Doldrums
the regions on either side of the equator where air pressure is low and winds are light.

Doppler Radar
A type of weather radar that determines whether atmospheric motion is toward or away from the radar. It determines the intensity of rainfall and uses the Doppler effect to measure the velocity of droplets in the atmosphere.

Downburst
A strong downdraft resulting in an outward burst of damaging winds on or near the ground. Downburst winds can produce damage similar to a strong tornado.

Downslope wind
Air that descends an elevated plain and consequently warms and dries. Occurs when prevailing wind direction is from the same direction as the elevated terrain and often produces fair weather conditions.

Drifting snow
Uneven distribution of snowfall caused by strong surface winds. Drifting snow does not reduce visibility.

Drought
Abnormally dry weather in a region over an extended period sufficient to cause a serious hydrological (water cycle) imbalance in the affected area. This can cause such problems as crop damage and water-supply shortage.

Dry Adiabat
A line of constant potential temperature on a thermodynamic chart.

Dry Punch
A surge of drier air; normally a synoptic-scale or mesoscale process. A dry punch at the surface results in a dry line bulge.

Dry Slot
A zone of dry (and relatively cloud-free) air which wraps east

Dust Whirl
A rotating column of air rendered visible by dust.

Easterly Wave
A wavelike disturbance in the tropical easterly winds that usually moves from east to west. Such waves can grow into tropical depressions.

ECMF
European Center for Meteorology Forecast model.