Advanced Hydrologic Prediction Service (AHPS)A web-based suite of accurate and information-rich forecast products. They display the magnitude and uncertainty of occurrence of floods or droughts, from hours to days and months in advance. These graphical products are useful information and planning tools for many economic and emergency managers.Area Hydrologic Discussion (AHD)A short range, episodic, discussion and graphic which highlights locations across the nation that may be impacted by rapid-onset flooding, using National Water Model and other guidance.Area Wide Hydrologic Prediction System(Abbrev. AWHPS) - A computer system which automatically ingests areal flash flood guidance values and WSR-88D products and displays this data and other hydrologic information on a map background.BNDRYBoundaryComposite HydrographA stream discharge hydrograph which includes base flow, or one which corresponds to a net rain storm of duration longer than one unit period.CSDRBLConsiderableCurtain DrainIn hydrologic terms, a drain constructed at the upper end of the area to be drained, to intercept surface or ground water flowing toward the protected area from higher ground, and carry it away from the area. Also called an Intercepting Drain. DendritesIn hydrologic terms, thin branch-like growth of ice on the water surface. DendriticIn hydrologic terms, the form of the drainage pattern of a stream and it's tributaries when it follows a treelike shape, with the main trunk, branches, and
twigs corresponding to the main stream, tributaries, and subtributaries, respectively, of the stream.DisdrometerEquipment that measures and records the size distribution of raindrops. 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.DoldrumsThe regions on either side of the equator where air pressure is low and winds are light.Downdraft(Abbrev. DWNDFT) - A small-scale column of air that rapidly sinks toward the ground, usually accompanied by precipitation as in a shower or thunderstorm. A downburst is the result of a strong
downdraft.DRDirectionDrainage AreaIn hydrologic terms, an area having a common outlet for its surface runoff (also see Watershed and Catchment Area).Drainage BasinIn hydrologic terms, a part of the surface of the earth that is occupied by a drainage system, which consists of a surface stream or a body of impounded
surface water together with all tributary surface streams and bodies of impounded surface water.Drainage DensityIn hydrologic terms, the relative density of natural drainage channels in a given area. It is usually expressed in terms of miles of natural drainage or
stream channel per square mile of area, and obtained by dividing the total length of stream channels in the area in miles by the area
in square miles.Drainage DivideIn hydrologic terms, the boundary line, along a topographic ridge or along a subsurface formation, separating two adjacent drainage basins.DrainerA valley or basin from which air drains continuously during nighttime rather than becoming trapped or pooled.
Drains (Relief Wells)In hydrologic terms, a vertical well or borehole, usually downstream of impervious cores, grout curtains or cutoffs, designed to collect and direct
seepage through or under a dam to reduce uplift pressure under or within a dam. A line of such wells forms a "drainage curtain".DrawdownIn hydrologic terms, the lowering of the surface elevation of a body of water, the water surface of a well, the water table, or the piezometric surface
adjacent to the well, resulting from the withdrawl of water therefrom.DRCTNDirectionDredgingIn hydrologic terms, the scooping, or suction of underwater material from a harbor, or waterway. Dredging is one form of channel modification. It is
often too expensive to be practical because the dredged material must be disposed of somewhere and the stream will usually fill
back up with sediment in a few years. Dredging is usually undertaken only on large rivers to maintain a navigation channel.DRFTDriftDrifting IceIn hydrologic terms, pieces of floating ice moving under the action of wind and/ or currents.Drifting SnowDrifting snow is an uneven distribution of snowfall/snow depth caused by strong surface winds. Drifting snow may occur during or after a snowfall. Drifting snow is usually associated with blowing snow.DrizzlePrecipitation consisting of numerous minute droplets of water less than 0.5 mm (500 micrometers) in diameter.Drop-size DistributionThe distribution of rain drops or cloud droplets of specified
sizes.DroughtDrought is a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area. NOAA together with its partners provides short- and long-term Drought Assessments.Drought AssessmentsAt the end of each month, CPC issues a long-term seasonal drought assessment. On Thursdays of each week, the CPC together with NOAA National Climatic Data Center, the United States Department of Agriculture, and the National Drought Mitigation Center in Lincoln, Nebraska, issues a weekly drought assessment called the United States Drought Monitor. These assessments review national drought conditions and indicate potential impacts for various economic sectors, such as agriculture and forestry.Drought IndexIn hydrologic terms, computed value which is related to some of the cumulative effects of a prolonged and abnormal moisture deficiency. (An index of
hydrological drought corresponding to levels below the mean in streams, lakes, and reservoirs.)Dry AdiabatA line of constant potential temperature on a thermodynamic chart.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.Dry CrackIn hydrologic terms, a crack visible at the surface but not going right through the ice cover, and therefore it is dry.Dry FloodproofingIn hydrologic terms, a dry floodproofed building is sealed against floodwaters. All areas below the flood protection level are made watertight. Walls are
coated with waterproofing compounds or plastic sheeting. Openings like doors windows, sewer lines and vents are closed, whether
permanently, with removable shields, or with sandbags. The flood protection level should be no more than 2 or 3 feet above the
top of the foundation because the buildings walls and floors cannot withstand the pressure of deeper water.Dry LineA boundary separating moist and dry air masses, and an important factor in
severe weather frequency in the Great Plains. It typically lies north-south across
the central and southern high Plains states during the spring and early summer,
where it separates moist air from the Gulf of Mexico (to the east) and dry desert
air from the southwestern states (to the west). The dry line typically advances
eastward during the afternoon and retreats westward at night. However, a strong
storm system can sweep the dry line eastward into the Mississippi Valley, or
even further east, regardless of the time of day.
A typical dry line passage results in a sharp drop in humidity (hence the name),
clearing skies, and a wind shift from south or southeasterly to west or
southwesterly. (Blowing dust and rising temperatures also may follow, especially
if the dry line passes during the daytime. These changes occur in reverse order
when the dry line retreats westward. Severe and sometimes tornadic
thunderstorms often develop along a dry line or in the moist air just to the east of
it, especially when it begins moving eastward.Dry Line BulgeA bulge in the dry line, representing the area where dry air is advancing most strongly at lower levels. Severe weather potential is increased near and ahead of a dry line bulge.Dry Line StormAny thunderstorm that develops on or near a dry line.Dry MicroburstA microburst with little or no precipitation reaching the ground; most common in semi-arid regions. They may or may not produce lightning. Dry microbursts may develop in an otherwise fair-weather pattern; visible signs may include a cumulus cloud or small Cb with a high base and high-level virga, or perhaps only an orphan anvil from a dying rain shower. At the ground, the only visible sign might be a dust plume or a ring of blowing dust beneath a local area of virga.Dry Punch[Slang], a surge of drier air; normally a synoptic-scale or mesoscale process. A dry punch at
the surface results in a dry line bulge. A dry punch aloft above an area of moist air at low levels often
increases the potential for severe weather.Dry SlotA zone of dry (and relatively cloud-free) air which wraps east- or northeastward into the southern and eastern parts of a synoptic scale or mesoscale low pressure system. A dry slot generally is seen best on satellite photographs.Dry ThunderstormGenerally a high-based thunderstorm when lightning is observed, but little if any precipitation reaches the ground. Most of the rain produced by the thunderstorm evaporates into relatively dry air beneath the storm cell. May also be referred to as "dry lightning". Dry Weather FlowIn 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 ground water flow.Dry-adiabatic1. An adiabatic process in a hypothetical atmosphere in which no moisture is present. 2. An adiabatic process in which no condensation of its water vapor occurs and no liquid water is present.Ensemble Hydrologic ForecastingIn hydrologic terms, a process whereby a continuous hydrologic model is successively executed several times for the same forecast period by use of
varied data input scenarios, or a perturbation of a key variable state for each model run. A common method employed to obtain a
varied data input scenario is to use the historical meteorological record, with the assumption that several years of observed data
covering the time period beginning on the current date and extending through the forecast period comprises a reasonable estimate
of the possible range of future conditions.Equilibrium DrawdownIn hydrologic terms, the ultimate, constant drawdown for a steady rate of pumped discharge.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.Forward Flank DowndraftThe main region of downdraft in the forward, or leading, part of a supercell, where most of the heavy precipitation is.
Freezing DrizzleA drizzle that falls as a liquid but freezes into glaze or rime upon contact with the cold ground or surface structures.Freezing Drizzle AdvisoryIssued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems. French DrainIn hydrologic terms, an underground passageway for water through the interstices among stones placed loosely in a trenchGDROn a buoy report, direction, in degrees clockwise from true North, of the GSP, reported at the last hourly 10-minute segment.GeohydrologyIn hydrologic terms, the branch of hydrology relating to subsurface, or subterranean waters.Ground Water HydrologyThe 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
waterGround Water OverdraftPumpage of ground water in excess of safe yield.HDRAINAn Hourly Digital Rainfall Product of the WSR-88D.Height Above the Nearest Drainage (HAND)A relative elevation methodology used in inundation mapping, which determines the height of every point on a land surface above the nearest stream reach to which it drains.HSA (Hydrologic Service Area)A geographical area assigned to Weather Service Forecast Office's/Weather Forecast Office's that embraces one or more rivers.Hydraulic Fill DamIn hydrologic terms, a dam constructed of materials, often dredged, that are conveyed and placed by suspension in flowing waterHydraulic FlowAtmospheric flow that is similar in character to the flow of water over an obstacle.Hydraulic Grade LineIn hydrologic terms, a line whose plotted ordinate position represents the sum of pressure head plus elevation head for the various positions along a
given fluid flow path, such as along a pipeline or a ground water streamline.Hydraulic HeadIn hydrologic terms,
(1) The height of the free surface of a body of water above a given point beneath the surface.
(2) The height of the water level at
the headworks, or an upstream point, of a waterway, and the water surface at a given point downstream.
(3) The height of a
hydraulic grade line above the center line of a pressure pipe, at a given point.Hydraulic JumpA steady disturbance in the lee of a mountain, where the airflow passing over the mountain suddenly changes from a region of low depth and high velocity to a region of high depth and low velocity.Hydraulic PermeabilityIn hydrologic terms, the flow of water through a unit cross-sectional area of soil normal to the direction of flow when the hydraulic gradient is unity.HydrometeorologyAn interdisciplinary science involving the study and analysis of the interrelationships between the atmospheric and land phases of water as it moves through the hydrologic cycle.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.Hydrologic BudgetIn hydrologic terms, an accounting of the inflow to, outflow from, and storage in, a hydrologic unit, such as a drainage basin, aquifer, soil zone, lake,
reservoir, or irrigation project. Hydrologic CycleThe description of the transport of water substance between the earth, the atmosphere, and the seas.
In hydrologic terms, the natural pathway water follows as it changes between liquid, solid, and gaseous states.Hydrologic Ensemble Forecast System (HEFS)A probabilistic forecast tool with the goals to provide hydrologic forecasts including an analysis of “probable outcomes” and to minimize biases in the atmospheric models and in the hydrologic models.Hydrologic EquationIn hydrologic terms, the water inventory equation (Inflow = Outflow + Change in Storage) which expresses the basic principle that during a given time
interval the total inflow to an area must equal the total outflow plus the net change in storage.Hydrologic ModelIn hydrologic terms, a conceptual or physically-based procedure for numerically simulating a process or processes which occur in a watershed.Hydrologic Service AreaHSA. A geographical area assigned to Weather Service Forecast Office's/Weather Forecast Office's that embraces one or more rivers.HydrologyThe scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water on or below the land surface.HydrometeorA particle of condensed water (liquid, snow, ice, graupel, hail) in the atmosphere.HydrometeorologistsIn hydrologic terms, individuals who have the combined knowledge in the fields of both meteorology and hydrology which enables them to study and
solve hydrologic problems where meteorology is a factor.HydrometeorologyAn interdisciplinary science involving the study and analysis of the interrelationships between the atmospheric and land phases of water as it moves through the hydrologic cycle.
Hydrostatic HeadIn hydrologic terms, a measure of pressure at a given point in a liquid in terms of the vertical height of a column of the same liquid which would produce
the same pressureIsodrosothermA line connecting points of equal dew point temperature.Keetch-Byrum Drought IndexAn index used to gage the severity of drought in deep duff and organic soils.Left Front QuadrantUsed interchangably with Left Exit Region; the area downstream from and to the left of an upper-level jet max (as would be viewed looking along the direction of flow). Upward motion and severe thunderstorm potential sometimes are increased in this area relative to the wind speed maximum. See also entrance region, right rear quadrant.National Hydrologic Discussion (NHD)A discussion of the current and forecast hydrologic conditions across the nation, including a variety of short and medium range (Days 1-10) observed and modeled hydrologic guidance.Palmer Drought Severity Index(Abbrev. PDSI) - an index used to gage the severity of drought conditions by using a water balance equation to track water supply and demand. This index is calculated weekly by the National Weather Service.Pressure-driven ChannelingChanneling of wind in a valley by synoptic-scale pressure gradients superimposed along the valley's axis. Compare forced channeling.QuadratureThe component of the complex signal that is 90 degrees out of phase with the inphase component. This component lies along the imaginary axis the complex plane.Rear Flank DowndraftA region of dry air subsiding on the back side of, and wrapping around, a mesocyclone. It often is visible as a clear slot wrapping around the wall cloud. Scattered large precipitation particles (rain and hail) at the interface between the clear slot and wall cloud may show up on radar as a hook or pendant; thus the presence of a hook or pendant may indicate the presence of an RFD.Right Rear Quadrant(Abbrev. RRQ) - Used interchangably with Right Entrance Region; the area upstream from and to the right of an upper-level jet max (as would be viewed looking along the direction of flow). Upward motion and severe thunderstorm potential sometimes are increased in this area relative to the wind speed maximum. See also exit region, left front quadrant. Satellite Hydrology ProgramA NOHRSC program that uses satellite data to generate areal extent of snow cover data over large areas of the western United States.Service HydrologistThe designated expert of the hydrology program at a WFO.Sustained OverdraftIn hydrologic terms, long-term withdrawal from the aquifer of more water than is being recharged.Terminal Aerodrome ForecastThis NWS aviation product is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each country is allowed to make modifications or exceptions to the code for use in each particular country. TAFs use the same weather code found in METAR weather reports.Thermally Driven CirculationA diurnally reversing closed cellular wind current resulting from horizontal temperature contrasts caused by different rates of heating or cooling over adjacent surfaces; includes along-slope, cross-valley, along-valley, mountain-plain and sea breeze circulations.Tilted UpdraftA thunderstorm updraft which is not purely vertical but instead exhibits a slanted or tilted character. It is a sign of vertical wind shear, a favorable condition for severe storm development.Unit HydrographThe discharge hydrograph from one inch of surface runoff distributed uniformly over the entire basin for a given time periodUnited States Drought Monitor (USDM)A multi-agency product that defines and highlights the severity of drought across the ConUS and OConUS based on expert interpretation of a multitude of indices.UpdraftA small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cb.VALDRIFTAn air pollution transport and diffusion model developed to determine pesticide drift from aerial spraying operations in valleys.
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