abrupt climate changea change in the climate (for example, temperature or precipitation) that takes place over a few decades or less, persists for at least a few decades, and…
absolute datingthe process of determining a specific, numerical age for an old material. This may be accomplished using one of a variety of methods, including…
Absolute HumidityThe ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air.
Absolutely Stable AirAn atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic lapse rate.
Absolutely Unstable AirAn atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic lapse rate.
Absorption(ub-SORP-shun) The process of taking nutrients from the digestive system into the blood so they can be used in the body.
Absorption of radiationThe uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted. See radiation.
absorptivityIn a solar thermal system, the ratio of solar energy striking the absorber that is absorbed by the absorber to that of solar energy striking a black body…
ACCAS(usually pronounced ACK-kis) - A lto C umulus CAS tellanus; mid-level clouds (bases generally 8 to 15 thousand feet), of which at least a fraction of…
Accessory CloudA cloud which is dependent on a larger cloud system for development and continuance.
AccretionProcess of growth whereby material is added to the outside of nonliving matter.
accumulationused in paleoclimatology to describe the deposition of sediment or other material over time.
AccuracyDepartment of Defense parlance for the notion that information has been maintained and transferred in such a way as to be inviolate (the information has…
Acid depositionA comprehensive term for the various ways acidic compounds precipitate from the atmosphere and deposit onto surfaces.
Acid PrecipitationPrecipitation, such as rain, snow or sleet, containing relatively high concentrations of acid-forming chemicals that have been released into the…
Acid RainA term used to describe precipitation that has become acidic (low pH) due to the emission of sulfur oxides from fossil fuel burning power plants.
Acid SolutionAny water solution that has more hydrogen ions (H+) than hydroxide ions (OH-); any water solution with a pH less than 7. See basic solution.
AcidicThe condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.
Acre-footOne surface acre of water 1 foot deep or 43,560 cubic feet of water. The total acre-feet of water in a pond is determined by multiplying the number of…
Action StageThe stage which, when reached by a rising stream, represents the level where the NWS or a partner/user needs to take some type of mitigation action in…
Active(abbrev. ACTV). In solar-terrestrial terms, solar activity levels with at least one geophysical event or several larger radio events (10cm) per day (Class…
Active Conservation StorageThe portion of water stored in a reservoir that can be released for all useful purposes such as municipal water supply, power, irrigation, recreation…
Active LongitudeIn solar-terrestrial terms, the approximate center of a range of heliographic longitudes in which Active Regions are more numerous and more flare-active…
Active ProminenceIn solar-terrestrial terms, a prominence displaying material motion and changes in appearance over a few minutes of time.
Active Region (AR)In solar-terrestrial terms, a localized, transient volume of the solar atmosphere in which plages, sunspots, faculae, flares, etc. may be observed.
Active Storage CapacityIn hydrologic terms, the total amount of reservoir capacity normally available for release from a reservoir below the maximum storage level.
Active Surge Region (ASR)In solar-terrestrial terms, an Active Region that exhibits a group or series of spike-like surges that rise above the limb.
actual evapotranspirationThe rate of water lost from vegetation and soil, ordinarily at a slower rate than the potential rate.
ACTVActive. In solar-terrestrial terms, solar activity levels with at least one geophysical event or several larger radio events (10cm) per day (Class M…
ACYCAnticyclone - A large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere…
AdaptationAdjustment of a population to changes in environment over generations, associated (at least in part) with genetic changes resulting from selection imposed…
ADAPTATION (ADAPTABLE) PARAMETERGenerally, data related to a specific WSR-88D unit. These data may consist of meteorological or hydrological parameters or of geographic boundaries…
Additive DataA group of coded remarks that includes pressure tendency, amount of precipitation, and maximum/minimum temperature during specified periods of time
AdiabatA line on a thermodynamic chart relating the pressure and temperature of a substance (such as air) that is undergoing a transformation in which no heat is…
AdiabaticWithout loss or gain of heat to a system. An adiabatic change is a change in volume and pressure of a parcel of gas without an exchange of heat between…
Adiabatic Lapse RateThe rate of decrease of temperature experienced by a parcel of air when it is lifted in the atmosphere under the restriction that it cannot exchange heat…
Adiabatic ProcessA process which occurs with no exchange of heat between a system and its environment.
Adirondack Type Snow Sampling SetA snow sampler consisting of a 5-foot fiberglass tube, 3 inches in diameter, with a serrated-edge steel cutter at one end and a twisting handle at the…
ADVCTNAdvection- Transport of an atmospheric property by the wind.
Advection(Abbrev. ADVCTN)- Transport of an atmospheric property by the wind.
Advection FogA fog that forms when warm air flows over a cold surface and cools from below until saturation is reached.
advective tendencyThe large-scale advective tendency of temperature and moisture used to force SCMs and CSRMs, derived from constrained variational analysis.
ADVISA program which combines the Antecedent Precipitation Index (API) method of estimating runoff with unit hydrograph theory to estimate streamflow for a…
Advisory(Abbrev. ADVY)- Highlights special weather conditions that are less serious than a warning.
ADVYAdvisory - Highlights special weather conditions that are less serious than a warning.
Aeration ZoneA portion of the lithosphere in which the functional interstices of permeable rock or earth are not filled with water under hydrostatic pressure.
AeroallergensAny of a variety of allergens such as pollens, grasses, or dust carried by winds.
AerobicIn biochemistry, reactions that need oxygen to happen or happen when oxygen is present.
AerosolA system of colloidal particles dispersed in a gas, such as smoke or fog.
aerosol absorptionThe process in which radiation energy is retained by aerosols.
aerosol Angstrom coefficientOften incorrectly used synonymously with "aerosol Angstrom exponent", but should instead refer to the aerosol optical depth at the reference wavelength (1…
aerosol Angstrom exponentThe exponent of the inverse power-law that approximates the wavelength dependence of aerosol optical depth.
AFDArea Forecast Discussion - This National Weather Service product is intended to provide a well-reasoned discussion of the meteorological thinking which…
AfforestationPlanting of new forests on lands that historically have not contained forests.
AfforestationsPlanting of new forests on lands that have not been recently forested.
AFOSAutomation of Field Operations and Services. Computer system linking NWS offices for the transmission of weather data.
AFREDAbbreviation for the A Index for Fredericksburg.
AfterbayThe tail race of a hydroelectric power plant at the outlet of the turbines. The term may be applied to a short stretch of stream or conduit, or to a pond…