Active Prominence Region (APR)In solar-terrestrial terms, a portion of the solar limb displaying active prominences.Active Storage CapacityIn hydrologic terms, the total amount of reservoir capacity normally available for release from a reservoir below the maximum storage level. It is total or reservoir capacity minus inactive storage capacity. More specifically, it is the volume of water between the outlet works and the spillway crest. ADAPTATION (ADAPTABLE) PARAMETERGenerally, data related to a specific WSR-88D unit. These data may consist of meteorological or hydrological parameters or of geographic boundaries, political boundaries, system configuration, telephone numbers (auto dial), or other like data. Such data may be generated at either a centralized location or locally at the WSR-88D unit. 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 with its environment. For parcels that remain unsaturated during lifting, the (dry adiabatic) lapse rate is 9.8°C per kilometer.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. When non-standard index-of-refraction distributions prevail, "abnormal" or "anomalous" propagation occurs. When abnormal downward bending occurs, it is called "superrefraction." If the beam is refracted downward sufficiently, it will illuminate the ground and return signals to the radar from distances further than is normally associated with ground targets. The term "subrefraction" is applied when there is abnormal upward bending of the radar beam.APAnomalous Propagation. Radar term for false (non-precipitation) echoes resulting from nonstandard
propagation of the radar beam under certain atmospheric conditions.AP IndexIn solar-terrestrial terms, an averaged planetary A Index based on data from a set of specific
stations.APDOn a buoy report, the average wave period (seconds) of all waves during the 20-minute period.AphelionThe point on the annual orbit of a body (about the sun) that is farthest from the sun; at present, the earth reaches this point (152 million kilometer from the sun) on about 5 July. Opposite of perihelion.API MethodIn hydrologic terms, a statistical method to estimate the amount of surface runoff which will occur from a basin from a given rainstorm based on the antecedent precipitation index, physical characteristics of the basin, time of year, storm duration, rainfall amount, and rainfall intensity. ApogeeThe farthest distance between the moon and earth or the earth and sun.Apparent TemperatureA measure of human discomfort due to combined heat and humidity (e.g., heat index).Apparent WindThe speed and true direction from which the wind appears to blow with reference to a moving point. Sometimes called RELATIVE WIND.APRCHApproachAPRCHGapproachingAPRNTapparentAPSTAviation Products and Services TeamArea-Capacity CurveIn hydrologic terms, a graph showing the relation between the surface area of the water in a reservoir, the corresponding volume, and elevation. ASAP1. AHOS SHEF Automatic Processing System
2. As soon as possible (may be used in Area Forecast Discussions)ASAPTRANThe software component of ASAP.BAPSUBay Area Public Service Unit. Public Service section of the San Francisco Bay Area Weather Service Forecast Office.BarographA barometer that records its observations continuously.Cap(also called "Lid") A layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development.Cap CloudA stationary cloud directly above an isolated mountain peak, with cloud base below the elevation of the peak.CAPEConvective Available Potential Energy. A measure of the amount of energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg.
However, as with other indices or indicators, there are no threshold values above which severe weather becomes imminent. CAPE is represented on an upper air sounding by the area enclosed between the environmental temperature profile and the path of a rising air parcel, over the layer within which the latter is warmer than the former. (This area often is called positive area.) See also CIN.CapillarityIn hydrologic terms,
1.The degree to which a material or object containing minute openings or passages, when immersed in a liquid, will draw the surface of the liquid above the hydrostatic level. Unless otherwise defined, the liquid is generally assumed to be water.
2. The phenomenon by which water is held in interstices above the normal hydrostatic level, due to attraction between water molecules. Capillary FringeIn hydrologic terms, the soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches, to a few feet, and it depends on the pore sizes of the materials. The capillary fringe is also called the capillary zone.Capillary WavesWaves caused by the initial wind stress on the water surface causes what are known as capillary waves. These have a wavelength of less than 1.73 cm, and the force that tries to restore them to equilibrium is the cohesion of the individual molecules. Capillary waves are important in starting the process of energy transfer from the air to the water. Capillary ZoneUsed interchangably with Capillary Fringe; the soil area just above the water table where water can rise up slightly through the cohesive force of capillary action. This layer ranges in depth from a couple of inches, to a few feet, and it depends on the pore sizes of the materials.CappingA region of negative buoyancy below an existing level of free convection (LFC) where energy must be supplied to the parcel to maintain its ascent.
This tends to inhibit the development of convection until some physical mechanism can lift a parcel to its LFC. The intensity of the cap is measured by its convective inhibition. The term capping inversion is sometimes used, but an inversion is not necessary for the conditions producing convective inhibition to exist.Capping InversionAlternate term for Cap; a layer of relatively warm air aloft, usually several thousand feet above the ground, which suppresses or delays the development of thunderstorms. Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further and produce thunderstorms. As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. However, if the cap is removed or weakened, then explosive thunderstorm development can occur.
The cap is an important ingredient in most severe thunderstorm episodes, as it serves to separate warm, moist air below and cooler, drier air above. With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability. But without a cap, either process (warming/moistening at low levels or cooling aloft) results in a faster release of available instability - often before instability levels become large enough to support severe weather development.CAPSCenter for Analysis and Prediction of StormsComposite HydrographA stream discharge hydrograph which includes base flow, or one which corresponds to a net rain storm of duration longer than one unit period.DAPM In hydrologic terms, the Data Acquisition Program Manager.Disappearing Solar Filament (DSF)In solar-terrestrial terms, the sudden (timescale of minutes to hours) disappearance of a solar filament (prominence).Distribution (Hydro)GraphIn hydrologic terms, a unit hydrograph of direct runoff modified to show the proportions of the volume of runoff that occur during successive equal units
of time.Dry Adiabatic Lapse RateThe rate at which the temperature of a parcel of dry air decreases as the parcel is lifted in the atmosphere. The dry adiabatic lapse rate (abbreviated DALR) is 5.5°F per 1000 ft or 9.8°C per km.Effective TopographyThe topography as seen by an approaching flow, which may include not only the actual terrain but also cold air masses trapped within or adjacent to the actual topography.Environmental Lapse RateThe rate of decrease of air temperature with height, usually measured with a radiosonde.EvaporationThe process of a liquid changing into a vapor or gas, usually water in meteorology.Evaporation PanIn hydrologic terms, a pan used to hold water during observations for the determination of the quantity of evaporation at a given location. Such pans are
of varying sizes and shapes, the most commonly used being circular or square.Evaporation RateIn hydrologic terms, the quantity of water, expressed in terms of depth of liquid water, which is evaporated from a given surface per unit of time. It is
usually expressed in inches depth, per day, month, or year.Evaporation-mixing FogFog that forms when the evaporation of water raises the dew point of the adjacent air.Evaporative Demand Drought Index (EDDI)An experimental drought monitoring and early warning guidance tool. It examines how anomalous the atmospheric evaporative demand is for a given location and across a time period of interest.EvaporimeterIn hydrologic terms, an instrument which measures the evaporation rate of water into the atmosphere.EvapotranspirationCombination of evaporation from free water surfaces and transpiration of
water from plant surfaces to the atmosphere.Exclusive Flood Control Storage CapacityIn hydrologic terms, the space in a reservoir reserved for the sole purpose of regulating flood inflows to abate flood damageField (Moisture) CapacityThe amount of water held in soil against the pull of gravityFlood Inundation Mapping (FIM)In the context of the National Water Model (NWM) FIM, the expected maximum inundation extent over a particular period of time derived using the Height Above Nearest Drainage (HAND) method. Stage heights are interpolated from the NWM discharge values using synthetic rating curves, and are rounded to the nearest foot.Gap WindsStrong 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.High Resolution Rapid Refresh (HRRR)A real-time 3-km resolution, hourly updated, cloud-resolving, convection-allowing atmospheric model, initialized by 3km grids with 3km radar assimilation.HodographA polar coordinate graph which shows the vertical wind profile of the lowest 7000 meters of the atmosphere. These plots are used to determine the advection patterns aloft, whether a thunderstorm will rotate, and the type of thunderstorms that you will likely see that day. HydrographIn hydrologic terms, a graph showing the water level (stage), discharge, or other property of a river volume with respect to time. Hydrograph SeparationIn hydrologic terms, the process where the storm hydrograph is separated into baseflow components and surface runoff components. Hydrographic SurveyIn hydrologic terms, an instrumental survey to measure and determine characteristics of streams and other bodies of water within an area, including such
things as location, areal extent, and depth of water in lakes or the ocean; the width, depth, and course of streams; position and
elevation of high water marks; location and depth of wells, etc.HyetographA graphical representation of rainfall intensity with respect to time.Inactive Storage CapacityIn hydrologic terms, the portion of capacity below which the reservoir is not normally drawn, and which is provided for
sedimentation, recreation, fish and wildlife, aesthetic reasons, or for the creation of a minimum controlled operational or power head in
compliance with operating agreements or restrictions.Infiltration CapacityIn hydrologic terms, the maximum rate at which water can enter the soil at a particular point under a given set of conditions.Lapse RateThe rate of change of an atmospheric variable, usually temperature, with height. A steep lapse rate implies a rapid decrease in temperature with height (a sign of instability) and a steepening lapse rate implies that destabilization is occurring.Live CapacityIn hydrologic terms, the total amount of storage capacity available in a reservoir for all purposes, from the dead storage level to the normal water or
normal pool level surface level. Does not include surcharge, or dead storage, but does include inactive storage, active conservation
storage and exclusive flood control storage.MAPMean Areal Precipitation- The average rainfall over a given area, generally expressed as an average depth over the area.MicrobarographA instrument designed to continuously record a barometer's reading of very small changes in atmospheric pressure. MLCAPEMean Layer CAPE - CAPE calculated using a parcel consisting of Mean Layer values of temperature and moisture from the lowest 100 mb above ground level. See Convective Available Potential Energy (CAPE).Moist Adiabatic Lapse Rate(abbrev. MALR)- The rate at which the temperature of a parcel of saturated air decreases as the parcel is lifted in the atmosphere. The moist adiabatic lapse rate (abbreviated MALR) is not a constant like the dry adiabatic lapse rate but is dependent on parcel temperature and pressure.Neap TideA minimum tide occurring at the first and third quarters of the moon.NOGAPSNavy Operational Global Atmospheric Prediction System; a 144-hour numerical model of the atmosphere run by the U.S. Navy twice daily.OceanographyThe study of the ocean, embracing and integrating all knowledge pertaining to the ocean's physical boundaries, the chemistry and physics of sea water, and marine biology.OrographicRelated to, or caused by, physical geography (such as mountains or sloping terrain).Orographic LiftingSame as Upslope Flow; occurs when air is forced to rise and cool due to terrain features such as hills or mountains. If the cooling is sufficient, water vapor condenses into clouds. Additional cooling results in rain or snow. It can cause extensive cloudiness and increased amounts of precipitation in higher terrain.Orographic PrecipitationPrecipitation which is caused by hills or mountain ranges deflecting the moisture-laden air masses upward, causing them to cool and precipitate their moisture.Orographic UpliftSame as Orographic Lifting; occurs when air is forced to rise and cool due to terrain features such as hills or mountains. If the cooling is sufficient, water vapor condenses into clouds. Additional cooling results in rain or snow. It can cause extensive cloudiness and increased amounts of precipitation in higher terrain. Orographic WavesA wavelike airflow produced over and in the lee of a mountain barrier.Parapet WallIn hydrologic terms, a solid wall built along the top of the dam for ornament, safety, or to prevent overtoppingPolar Cap Absorption (PCA)In solar-terrestrial terms, an anomalous condition of the polar ionosphere whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 - 300 kHz) radiowaves are reflected at lower altitudes than normal. In practice, the absorption is inferred from the proton flux at energies greater than 10 MeV, so that PCAs and
proton events are simultaneous. Transpolar radio paths may still be disturbed for days, up to weeks, following the end of a proton event.Pressure Falling RapidlyA decrease in station pressure at a rate of 0.06 inch of mercury or more
per hour which totals 0.02 inch or more.Pressure Rising RapidlyAn increase in station pressure at a rate of 0.06 inch of mercury or more per hour which totals 0.02 inch or more.RADAP IIRAdar DAta Processor II, attached to some WSR-57 and WSR-74 radar units. It
automatically controls the tilt sequence and computes several radar-derived quantities at regular intervals,
including VIL, storm tops, accumulated rainfall, etc.Rapid DeepeningA decrease in the minimum sea-level pressure of a tropical cyclone of 1.75 mb/hr or
42 mb for 24 hoursRapid Onset Flooding (ROF)In the context of the National Water Model (NWM), rapid onset flooding refers to stream reaches that are forecast to at least double their flow within an hour, and meet or exceed their high water flow within six hours of this flow increase.Rapidly IntensifyingAny maritime cyclone whose central pressure is dropping, or is expected to drop, at a rate of 1 MB per hour for 24 hours. Saturation Vapor PressureThe vapor pressure of a system, at a given temperature, wherein the vapor of a substance is in equilibrium with a plane surface of that substance's pure liquid or solid phase.SBCAPESurface Based CAPE; CAPE calculated using a Surface based parcel.Sediment Storage CapacityIn hydrologic terms, the volume of a reservoir planned for the deposition of sediment.Storm Relative Mean Radial Velocity Map(SRM): This WSR-88D radar product depicts a full 360º sweep of radial velocity data with the average motion of all identified storms subtracted out. It is available for every elevation angle sampled. It is used to aid in displaying shear and rotation in storms and storm top divergence that might otherwise be obscured by the storm's motion, investigate the 3-D velocity structure of a storm, and help with determining rotational features in fast and uniform moving storms. Straight-Line HodographThe name pretty well describes what it looks like on the hodograph. What causes this shape is a steady increase of winds with height (vertical wind shear). This shape of hodograph favors multicell thunderstorms.Surcharge CapacityIn hydrologic terms, the volume of a reservoir between the maximum water surface elevation for which the dam is designed and the crest of an
uncontrolled spillway, or the normal full-pool elevation of the reservoir with the crest gates in the normal closed position.Synthetic Aperture Radar (SAR)A radar mounted on a moving platform (aircraft or satellite) used for imaging. Since the radar antenna moves a significant distance between transmission and receiving the signal back, the radar antenna acts as if it is larger than its physical dimensions, providing better range and azimuth resolution.Synthetic Aperture Radar River Ice Surveillance (SARRIS)An experimental river ice mapping experiment using Synthetic Aperture Radar (SAR).ThermographAn instrument that measures and records air temperature.TopographyThe shape of the land.TrapperA valley or basin in which cold air becomes trapped or pooled.Unit HydrographThe discharge hydrograph from one inch of surface runoff distributed uniformly over the entire basin for a given time periodUniversal Geographic Code(UGC) - UGC's, (e.g. ANZ300 for Western Long Island Sound) are used in many National Weather Service text products to provide geographical information. This allows users easy automated processing and redistribution of the information. More specifically, the purpose of the UGC are to specify the affected geographic area of the event, typically by state, county (or parish), or unique NWS zone (land and marine). The only exception to the above is to define the weather synopsis part of certain marine products. Vapor PressureThe partial pressure of water vapor in an air-water system.Variable Infiltration Capacity (VIC)A large-scale, semi-distributed hydrologic model that solves full water and energy balances. As such, it shares several basic features with other land surface models that are commonly coupled to global circulation models.Water Vapor PlumeThis appears in the water vapor satellite imagery. It is a plume-like object that extends from the Intertropical Convergence Zone (ITCZ) northward or southward into the higher latitudes. It is usually located over a 850 to 700 mb theta-e ridge axis. As a result, it is a favored location for the development of a Mesoscale Convective Complex (MCC). Researchers have found it to be a favored region for very heavy rain. It is thought that the ice crystals located in this plume help thunderstorms to become highly efficient rainfall producers. In North America, this is sometimes called the "Mexican Connection".WhitecapThe breaking crest of a wave, usually white and frothy.Wrapping Gust FrontA gust front which wraps around a mesocyclone, cutting off the inflow of warm moist air to the mesocyclone circulation and resulting in an occluded mesocyclone.
You can either type in the word you are looking for in the box below or browse by letter.
Browse by letter:# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z