AHOS-SAutomatic Hydrologic Observing System - Satellite
AHOS-TAutomatic Hydrologic Observing System - Telephone
AirThe mixture of gases that surrounds the earth and forms its atmosphere, composed of, by volume, 21 percent oxygen, 78 percent nitrogen.
Air carrierAn operator (e.g., airline) in the commercial system of air transportation consisting of aircraft that hold certificates of, Public Convenience and…
air densityThe mass per unit volume of air; about 1.275 kilometer per cubic meter at 0° C and 1000 millibars.
Air MassA body of air covering a relatively wide area and exhibiting horizontally uniform properties.
Air Mass ThunderstormGenerally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism.
Air pollutantAny substance in the air which could, if in high enough concentration, harm humans, other animals, vegetation, or material.
Air PollutionThe presence of contaminants in the air in concentrations that prevent the normal dispersive ability of the air, and that interfere with biological…
Air Pollution PotentialThe meteorological potential for air pollution problems, considered without regard to the presence or absence of actual pollution sources.
Air PressureSpecifically the air pressure of the tires. Changing the air pressure in the tires is a way to alter the setup and handling of a NASCAR race car.
Air Quality ModelMathematical or conceptual model used to estimate present or future air quality.
Air StagnationA meteorological situation in which there is a major buildup of air pollution in the atmosphere.
Air Stagnation AdvisoryThis National Weather Service product is issued when major buildups of air pollution, smoke, dust, or industrial gases are expected near the ground for a…
Air temperatureAir temperature (Also termed surface temperature in meteorology). The ambient temperature indicated by a thermometer exposed to the air but sheltered from…
Air Transportable Mobile UnitA modularized transportable unit containing communications and observational equipment necessary to support a meteorologist preparing on-site forecasts at…
Airborne Snow Survey ProgramCenter (NOHRSC) program that makes airborne snow water equivalent and soil moisture measurements over large areas of the country that are subject to…
Alaska CurrentA North Pacific Ocean current flowing counterclockwise in the Gulf of Alaska. It is the northward flowing (warm) division of the Aleutian Current
AlbedoThe ratio of light reflected by a surface to the light falling on it.
Alberta ClipperA fast moving low pressure system that moves southeast out of Canadian Province of Alberta (southwest Canada) through the Plains, Midwest, and Great Lakes…
Alberta LowAlberta Low A low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada.
ALERTAutomated Local Event Reporting in Real Time. Network of automatic raingauges that transmit via VHF radio link when precipitation occurs.
Alert StageThe elevation, or stage, of a stream at which need-to-know officials (e.g., county sheriff, civil defense officials, bypass gate operators) are notified…
Aleutian CurrentAn eastward flowing North Pacific Ocean current which lies north of the North Pacific Current.
Aleutian LowA semi-permanent, subpolar area of low pressure located in the Gulf of Alaska near the Aleutian Islands.
AlgorithmA detailed formula or set of steps for solving a particular problem. To be an algorithm, a set of rules must be unambiguous and have a clear stopping…
ALIASINGWhen computer graphics output has jagged edges or a stair-stepped, rather than a smooth, appearance when magnified.
AlkalinityThe total concentration of bases in water.
Alliance of Small Island States (AOSIS)The group of Pacific and Caribbean nations who call for relatively fast action by developed nations to reduce greenhouse gas emissions.
AlluviumDeposits of clay, silt, sand, gravel, or other particulate materials that have been deposited by a stream or other body of running water in a streambed…
Along-slope Wind SystemA closed, thermally driven diurnal mountain wind circulation whose lower branch blows up or down the sloping sidewalls of a valley or mountain.
AltimeterAn instrument that indicates the altitude of an object above a fixed level. Pressure altimeters use an aneroid barometer with a scale graduated in…
Altimeter SettingA correction of the station pressure to sea level used by aviation. This correction takes into account the standard variation of pressure with height and…
AltocumulusA cloud of a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of…
AltostratusA cloud of a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus.
AmbientSurrounding natural conditions or environment at a given place and time. Environmental or surrounding conditions.
Ambient AirThe air external to a building or device.
AMVERAutomated Mutual Assistance Vessel Rescue System. A system operated by the U.S.
AMVER/SEASA software program created by the National Weather Service intended to efficiently generate AMVER and VOS reports as part of a cooperative effort.
AnabranchA diverging branch of a river which re-enters the main stream.
AnaerobicAn environment or condition in which molecular oxygen is not available for chemical, physical or biological processes.
Anaerobic decompositionThe breakdown of molecules into simpler molecules or atoms by microorganisms that can survive in the partial or complete absence of oxygen.
Anaerobic LagoonA holding pond for livestock manure that is designed to anaerobically stabilize manure, and may be designed to capture biogas, with the use of an…
Anaerobic organismAn organism that does not need oxygen to stay alive. See anaerobic.
analogIn chemistry, a substance that is similar, but not identical, to another.
analog signalA signal, such as voice, that varies in a continuous manner.
AnalysisA process in which anything complex is separated into simple or less complex parts.
Anchor IceSubmerged Frazil ice attached or anchored to the river bottom, irrespective of its formation.
Anchor Ice DamAn accumulation of anchor ice which acts as a dam and raises the water level.
AnemometerAn instrument for measuring the force or velocity of wind; a wind gauge.
AnemorumbographAnemorumbograph Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed.
AnemorumbometerAnemorumbometer Russian anemometer combined with a vane to determine the wind direction.
Aneroid BarometerAn instrument for measuring atmospheric pressure in which a needle, attached to the top of an evacuated box, is deflected as changes in atmospheric…
AngelsRadar echoes caused by birds, insects, and localized refractive index discontinuities.
Angle of ReflectionThe angle at which a reflected ray of energy leaves a reflecting surface. It is measured between the outgoing ray and a perpendicular to the surface at…
Annex I Countries/PartiesGroup of countries included in Annex I (as amended in 1998) to the United Nations Framework Convention on Climate Change, including all the developed…
Annex I PartiesIndustrialized countries that, as parties to the Framework Convention on Climate Change, have pledged to reduce their greenhouse gas emissions by the year…
Annual FloodThe maximum discharge peak during a given water year (October 1 - September 30).
anomaliesThe departures of temperature, precipitation, or other weather elements from long-term averages.
ANOMALOUS PROPAGATION (AP)Non-standard atmospheric temperature or moisture gradients will cause all or part of the radar beam to propagate along a non-normal path.
AnomalySomething that is out of the ordinary. For example if in a set of 1000 two winged, two legged, one headed, (essentially normal) chickens, one of them had…
Antarctic "Ozone Hole"Refers to the seasonal depletion of stratospheric ozone in a large area over Antarctica. See ozone, ozone layer.
ANTENNA GAINThe measure of effectiveness of a directional antenna as compared to an isotropic radiator, maximum value is called antenna gain by convention.
AnthelionA luminous white spot that appears on the parhelic circle at the same altitude as the sun and 180 degrees from it in azimuth.
AnthraciteA hard, black, lustrous coal containing a high percentage of fixed carbon and a low percentage of volatile matter. Often referred to as hard coal.
AnthropogenicReferring to alterations in the environment due to the presence or activities of humans.
Anti-windThe upper or return branch of an along-valley wind system, as confined within a valley, and blowing in a direction opposite to the winds in the lower…
AnticyclogenesisThe formation or intensification of an anticyclone or high pressure center.
AnticycloneA large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the…
Anticyclonic circulationAnticyclonic circulation System of air movements (atmospheric circulation) associated with an anticyclone, which is clockwise in the Northern Hemisphere…
Anticyclonic RotationRotation in the opposite sense as the Earth's rotation, i.e., clockwise in the Northern Hemisphere as would be seen from above.
Antilles CurrentA current which originates in the vicinity of the Leeward Islands as part of the Atlantic North Equatorial Current.
AnvilThe flat, spreading top of a cumulonimbus cloud, often shaped like an anvil. Thunderstorm anvils may spread hundreds of miles downwind from the…
Anvil Crawler[Slang], a lightning discharge occurring within the anvil of a thunderstorm, characterized by one or more channels that appear to crawl along the…
Anvil DomeA large overshooting top or penetrating top.
Anvil RolloverSlang for a circular or semicircular lip of clouds along the underside of the upwind part of a back-sheared anvil, indicating rapid expansion of the anvil.
Anvil ZitsSlang for frequent (often continuous or nearly continuous), localized lightning discharges occurring from within a thunderstorm anvil.