• Weather Glossary (D)

    From Daryl Stout@57:57/10 to All on Fri Oct 16 00:06:14 2020
    This weather glossary contains information on more than 2000 terms,
    phrases and abbreviations used by the National Weather Service (NWS)...
    the government agency who makes weather forecasts, and issues weather advisories, watches, and warnings, for the United States, and its

    Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and
    before many NWS products were directly available to the public. It is the purpose of this glossary to aid you in better understanding NWS products.



    D Region
    In solar-terrestrial terms, a daytime layer of the earth's ionosphere approximately 50 to 90 km in altitude.

    Daily Climatological Report
    As the name indicates, this climatological product is issued daily by
    each National Weather Service office. Most of the climatological data
    in this report are presented in a tabular form; however, some narrative statements may also be used in the product. The report is organized so
    that similar items are grouped together (i.e., temperature, precipitation, wind, sunrise and sunset times, etc.).

    Daily Flood Peak
    In hydrologic terms, the maximum mean daily discharge occuring in a
    stream during a given flood event.

    Dry Adiabatic Lapse Rate

    In hydrologic terms, any artificial barrier which impounds or diverts
    water. The dam is generally hydrologically significant if it is:

    1. 25 feet or more in height from the natural bed of the stream and has a storage of at least 15 acre-feet.
    2. Or has an impounding capacity of 50 acre-feet or more and is at least
    six feet above the natural bed of the stream.

    Dam Failure
    In hydrologic terms, catastrophic event characterized by the sudden,
    rapid, and uncontrolled release of impounded water.

    In hydrologic terms, the Dam Break Forecasting Model.

    In hydrologic terms, the Data Acquisition Program Manager.

    Dark Surge on Disk (DSD)
    In solar-terrestrial terms, dark gaseous ejections visible in H-alpha.

    Dart Leader
    A faint, negatively charged channel that travels more or less directly
    and continuously from cloud to ground.

    Data Point
    In the context of hydrologic observations, a location on a river/stream
    for which observed data is input to RFC or WFO hydrologic forecast
    procedures, or included in public hydrologic products. Flood forecasts
    and warnings are not issued for data points.

    In hydrologic terms, the Software System that supports RFC gateway

    In hydrologic terms, it is the hydrologic Data Network Analysis Software.

    Same as Civil Dawn; the time of morning at which the sun is 6 below
    the horizon. At this time, there is enough light for objects to
    be distiguishable and that outdoor activities can commence.

    Day Length
    Duration of the period from sunrise to sunset.

    Nondimensional "unit" of radar reflectivity which represents a
    logarithmic power ratio (in decibels, or dB) with respect to radar
    reflectivity factor, Z.

    (Data Collection Platform) In hydrologic terms, an electronic device
    that connects to a river or rainfall gage that records data from the
    gage and at pre-determined times transmits that data through a
    satellite to a remote computer.

    Data Distribution System.

    Dead Storage
    In hydrologic terms, the volume in a reservoir below the lowest
    controllable level.

    Debris Cloud
    A rotating "cloud" of dust or debris, near or on the ground, often
    appearing beneath a condensation funnel and surrounding the base of
    a tornado. This term is similar to dust whirl, although the latter
    typically refers to a circulation which contains dust but not
    necessarily any debris. A dust plume, on the other hand, does not
    rotate. Note that a debris cloud appearing beneath a thunderstorm
    will confirm the presence of a tornado, even in the absence of a
    condensation funnel.

    Occurring over a 10-year period, such as an oscillation whose period is
    roughly 10 years ("Pacific Decadal Oscillation").

    The latitude that the sun is directly over at a given time. The
    declination is approximately 23 N at the summer solstice, approximately
    23 S at the winter solstice, and 0 (over the equator) at the spring
    and autumn equinoxes.

    Deep Percolation Loss
    In hydrologic terms, water that percolates downward through the soil
    beyond the reach of plant roots.

    Deep Seepage
    In hydrologic terms, infiltration which reaches the water table.

    Deep well
    In hydrologic terms, a well whose pumping head is too great to permit
    use of a suction pump.

    A decrease in the central pressure of a surface low pressure system. The
    storm is intensifying.

    Deformation Zone
    The change in shape of a fluid mass by variations in wind, specifically
    by stretching and/or shearing. Deformation is a primary factor in
    frontogenesis (evolution of fronts) and frontolysis (decay of fronts).

    Deformed Ice
    In hydrologic terms, a general term for ice which has been squeezed
    together and forced upwards and downwards in places. Subdivisions are
    rated ice, ridge ice, hummocked ice, and other similar deformations.

    In hydrologic terms, the geologic process by means of which various
    parts of the surface of the earth are worn down and carried away and
    their general level lowered, by the action of wind and water.

    Degree Day
    A measure that gauges the amount of heating or cooling needed for a
    building using 65 as a baseline. Electrical, natural gas, power,
    and heating, and air conditioning industries utilize heating and cooling
    degree information to calculate their needs. For more specific
    definitions and how to calculate degree days, see the definitions for
    Heating Degree Days and Cooling Degree Days.

    In hydrologic terms, an alluvial deposit, often in the shape of the
    Greek letter "delta", which is formed where a stream drops its debris
    load on entering a body of quieter water.

    Delta T
    Change in temperature.

    1) A simple representation of the mean lapse rate within a layer of the atmosphere, obtained by calculating the difference between observed temperatures at the bottom and top of the layer. Delta Ts often are
    computed operationally over the layer between pressure levels of 700 mb
    and 500 mb, in order to evaluate the amount of instability in mid-levels
    of the atmosphere. Generally, values greater than about 18 indicate
    sufficient instability for severe thunderstorm development.

    2) The difference in temperature between the surface of a lake and 850mb, typically used to determine lake effect snow potential.

    In hydrologic terms, thin branch-like growth of ice on the water surface.

    In hydrologic terms, the form of the drainage pattern of a stream and its 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.

    Dense Fog Advisory
    Issued when fog reduces visibility to 1/8 mile or less over a widespread

    Density Current
    In hydrologic terms, a flow of water maintained by gravity through a
    large body of water, such as a reservoir or lake, and retaining its
    unmixed identity because of a difference in density.

    Density of Snow
    In hydrologic terms, the ratio, expressed as a percentage, of the volume
    which a given quantity of snow would occupy if it were reduced to water,
    to the volume of the snow. When a snow sampler is used, it is the ratio expressed as percentage of the scale reading on the sampler to the length
    of the snow core or sample.


    Depletion Curve
    In hydrologic terms, the part of the hydrograph extending from the point
    of termination of the Recession Curve to the subsequent rise or
    alternation of inflow due to additional water becomming available for
    stream flow.

    A region of low atmospheric pressure that is usually accompanied by low
    clouds and precipitation. The term is also sometimes used as a reference
    to a Tropical Depression.

    Depression Storage
    In hydrologic terms, the volume of water contained in natural depressions
    in the land surface, such as puddles.

    Depth of Runoff
    In hydrologic terms, the total runoff from a drainage basin, divided by
    its area. For convenience in comparing runoff with precipitation, the
    term is usually expressed in inches of depth during a given period of
    time over the drainage area or acre-feet per square mile.

    (Pronounced day-RAY-cho), a widespread and usually fast-moving windstorm associated with convection. Derechos include any family of downburst
    clusters produced by an extratropical MCS, and can produce damaging straight-line winds over areas hundreds of miles long and more than
    100 miles across.

    Derived Products
    Processed base data on the Doppler radar.

    A tendency toward more prominent desert conditions in a region.

    Design Criteria
    In hydrologic terms, the hypothetical flood used in the sizing of the
    dam and the associated structures to prevent dam failure by overtopping, especially for the spillway and outlet works.

    Detention Basins
    In hydrologic terms, structures which are built upstream from a
    populated area so that precipitation flows do not flood and cause the
    loss of life or property. They are normally dry, but are designed to
    detain surface water temporarily during, and immediately after a runoff
    event. Their primary function is to attenuate the storm flows by
    releasing flows at a lower flow rate. There are no gates or valves
    allowed on the outlet so that water can never be stored on a long-term
    basis. Typical detention times in such a basin would be on the order of
    24 to 72 hours although some are as long as 5 to 10 days.

    Detention Storage
    In hydrologic terms, the volume of water, other than depression storage, existing on the land surface as flowing water which has not yet reached
    the channel.

    In hydrologic terms,

    (1) the heavier mineral debris moved by natural watercourses, usually in bed-load form.

    (2) the sand, grit, and other coarse material removed by differential sedimentation in a relatively short period of detention.

    Developing Gale/Storm
    In the high seas and offshore forecasts, a headline used in the warnings section to indicate that gale/storm force winds are not now occurring but
    are expected before the end of the forecast period.

    Moisture that has condensed on objects near the ground, whose temperatures
    have fallen below the dewpoint temperature.

    Dew Point
    (Abbrev. DWPT) - A measure of atmospheric moisture. It is the temperature
    to which air must be cooled in order to reach saturation (assuming air
    pressure and moisture content are constant). A higher dew point indicates
    more moisture present in the air. It is sometimes referred to as Dew Point Temperature, and sometimes written as one word (Dewpoint).

    Dew Point Depression
    The difference in degrees between the air temperature and the dew point.

    Dew Point Front
    A narrow zone (mesoscale feature) of extremely sharp moisture gradient
    and little temperature gradient. It separates moist air from dry air.
    Severe weather can be associated with this front. It is also known as a "dryline" or "dry front".

    On a buoy report, the dewpoint temperature taken at the same height as
    the air temperature measurement.


    A process which occurs with the addition or loss of heat. The opposite of adiabatic. Meteorological examples include air parcels warming due to the absorption of infrared radiation or release of latent heat.

    Diablo Wind
    Similar to Santa Ana winds in southern California. These winds occur
    below canyons in the East Bay hills (Diablo range) and in extreme cases
    can exceed 60 mph. They develop due to high pressure over Nevada and
    lower pressure along the central California coast.

    Diagnostic Model
    A computer model used to calculate air pollution concentrations. A
    diagnostic model produces a wind field over an area by interpolating
    from actual wind observations.

    Diamond Dust
    A fall of non-branched (snow crystals are branched) ice crystals in the
    form of needles, columns, or plates.

    Differential Motion
    Cloud motion that appears to differ relative to other nearby cloud
    elements, e.g. clouds moving from left to right relative to other clouds
    in the foreground or background. Cloud rotation is one example of
    differential motion, but not all differential motion indicates rotation.
    For example, horizontal wind shear along a gust front may result in differential cloud motion without the presence of rotation.

    Differential Rotation
    In solar-terrestrial terms, the change in solar rotation rate with
    latitude. Low latitudes rotate at a faster angular rate (approx. 14
    degrees per day) than do high latitudes (approx. 12 degrees per day).

    Diffuse Ice
    In hydrologic terms, poorly defined ice edge limiting an area of
    dispersed ice; usually on the leeward side of an area of floating ice.

    (or diffluence) - A pattern of wind flow in which air moves outward
    (in a "fan-out" pattern) away from a central axis that is oriented
    parallel to the general direction of the flow. It is the opposite of confluence.

    Difluence in an upper level wind field is considered a favorable
    condition for severe thunderstorm development (if other parameters are
    also favorable). But difluence is not the same as divergence. In a
    difluent flow, winds normally decelerate as they move through the region
    of difluence, resulting in speed convergence which offsets the apparent diverging effect of the difluent flow.


    1. Direction

    2. On a buoy report, the ten-minute average wind direction measurements
    in degrees clockwise from true North.

    Direct Flood Damage
    In hydrologic terms, the damage done to property, structures, goods, etc.,
    by a flood as measured by the cost of replacement and repairs.

    Direct Hit
    A close approach of a tropical cyclone to a particular location. For
    locations on the left-hand side of a tropical cyclone's track (looking in
    the direction of motion), a direct hit occurs when the cyclone passes to
    within a distance equal to the cyclone's radius of maximum wind. For
    locations on the right-hand side of the track, a direct hit occurs when
    the cyclone passes to within a distance equal to twice the radius of
    maximum wind. Compare indirect hit, strike.

    Direct Runoff
    In hydrologic terms, the runoff entering stream channels promptly after rainfall or snowmelt. Superposed on base runoff, it forms the bulk of the hydrograph of a flood.

    Direct Solar Radiation
    The component of solar radiation received by the earth's surface only
    from the direction of the sun's disk (i.e. it has not been reflected,
    refracted or scattered).

    Directional Shear
    The component of wind shear which is due to a change in wind direction
    with height, e.g., southeasterly winds at the surface and southwesterly
    winds aloft. A veering wind with height in the lower part of the
    atmosphere is a type of directional shear often considered important
    for tornado development.

    Disappearing Solar Filament (DSF)
    In solar-terrestrial terms, the sudden (timescale of minutes to hours) disappearance of a solar filament (prominence).

    In hydrologic terms, the rate at which water passes a given point.
    Discharge is expressed in a volume per time with units of L3/T.
    Discharge is often used interchangeably with streamflow.

    Discharge Curve
    In hydrologic terms, a curve that expresses the relation between the
    discharge of a stream or open conduit at a given location and the stage
    or elevation of the liquid surface at or near that location. Also called
    Rating Curve and Discharge Rating Curve.

    Discharge Table
    In hydrologic terms,

    1. A table showing the relation between two mutually dependant quantities
    or variable over a given range of magnitude.

    2. A table showing the relation between the gage height and the discharge
    of a stream or conduit at a given gaging station. Also called a Rating

    Equipment that measures and records the size distribution of raindrops.

    The visible surface of the sun (or any heavenly body) projected against
    the sky.

    The process of separating radiation into various wavelengths.

    Distribution (Hydro)Graph
    In 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.

    Daily; related to actions which are completed in the course of a calendar
    day, and which typically recur every calendar day (e.g., diurnal
    temperature rises during the day, and diurnal falls at night).

    Diurnal Cycles
    Variations in meteorological parameters such as temperature and relative humidity over the course of a day which result from the rotation of the
    Earth about its axis and the resultant change in incoming and outgoing radiation.

    Diurnal Temperature Range
    The temperature difference between the minimum at night (low) and the
    maximum during the day (high).

    The expansion or spreading out of a vector field; usually said of
    horizontal winds. It is the opposite of convergence. Divergence at upper
    levels of the atmosphere enhances upward motion, and hence the potential
    for thunderstorm development (if other factors also are favorable).

    In hydrologic terms, the taking of water from a stream or other body of
    water into a canal, pipe, or other conduit.

    In hydrologic terms, the high ground that forms the boundary of a
    watershed. A divide is also called a ridge.

    Dividing Streamline
    In the blocked flow region upwind of a mountain barrier, the streamline
    that separates the blocked flow region near the ground from the
    streamlines above which go over the barrier.

    Dividing Streamline Height
    The height above ground of the dividing streamline, as measured far
    upwind of a mountain barrier. See dividing streamline.



    Department of Natural Resources



    Dobson Unit
    Unit used to measure the abundance of ozone in the atmosphere. One Dobson
    unit is the equivalent of 2.69/ x 1016 molecules of ozone/cm2.

    Department of Commerce

    Development and Operations Hydrologist

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

    In air pollution modeling, the geographical area over which a simulation
    is performed.

    Domestic Consumption
    In hydrologic terms, the quantity, or quantity per capita, of water
    consumed in a municipality or district for domestic uses or purposes
    during a given period, generally one day. It is usually taken to include
    all uses included within the term Municipal Use of Water and quantity
    wasted, lost, or otherwise unaccounted for.

    Domestic Use of water
    In hydrologic terms, the use of water primarily for household purposes,
    the watering of livestock, the irrigation of gardens, lawns, shrubbery,
    etc., surrounding a house or domicile.

    Doppler Radar
    Radar that can measure radial velocity, the instantaneous component of
    motion parallel to the radar beam (i.e., toward or away from the radar antenna).

    Down-Valley Wind
    A thermally driven wind directed down a valley's axis, usually occurring
    during nighttime; part of the along-valley wind system.

    A strong downdraft current of air from a cumulonimbus cloud, often
    associated with intense thunderstorms. Downdrafts may produce damaging
    winds at the surface.

    (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.

    Downslope Flow
    A thermally driven wind directed down a mountain slope and usually
    occurring at night; part of the along-slope wind system.

    In the same direction as a stream or other flow, or toward the direction
    in which the flow is moving.

    Downstream Slope
    In hydrologic terms, the slope or face of the dam away from the
    reservoir water. This slope requires some kind of protection
    (e.g.; grass) from the erosive effects of rain and surface flow.

    A deflection of air downward relative to an object that causes the

    Downwelling Radiation
    The component of radiation directed toward the earth's surface from
    the sun or the atmosphere, opposite of upwelling radiation.


    1. Deep

    2. Dew Point

    On a buoy report, dominant wave period (seconds) is the period with the
    maximum wave energy.





    Drainage Area
    In hydrologic terms, an area having a common outlet for its surface
    runoff (also see Watershed and Catchment Area).

    Drainage Basin
    In 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 Density
    In 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 Divide
    In hydrologic terms, the boundary line, along a topographic ridge or
    along a subsurface formation, separating two adjacent drainage basins.

    A 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".

    In 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


    In 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.


    Drifting Ice
    In hydrologic terms, pieces of floating ice moving under the action of
    wind and/ or currents.

    Drifting Snow
    Drifting 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.

    Precipitation consisting of numerous minute droplets of water less than
    0.5 mm (500 micrometers) in diameter.

    Drop-size Distribution
    The distribution of rain drops or cloud droplets of specified sizes.

    Drought 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 Assessments
    At 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 Index
    In 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 Adiabat
    A line of constant potential temperature on a thermodynamic chart.

    Dry Adiabatic Lapse Rate
    The 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 Crack
    In hydrologic terms, a crack visible at the surface but not going right
    through the ice cover, and therefore it is dry.

    Dry Floodproofing
    In 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 Line
    A 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 Bulge
    A 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 Storm
    Any thunderstorm that develops on or near a dry line.

    Dry Microburst
    A 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 Slot
    A 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 Thunderstorm
    Generally 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 Flow
    In 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


    1. 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.

    Special Tropical Disturbance Statement


    Dst Index
    A geomagnetic index describing variations in the equatorial ringcurrent.


    Duration Curve
    In hydrologic terms, a cumulative frequency curve that shows the percent
    of time during which specified units of items (e.g. discharge, head, power,etc.) were equaled or exceeded in a given period. It is the
    integral of the frequency diagram.

    Duration of Ice Cover
    In hydrologic terms, The time from freeze-up to break-up of an ice cover.

    Duration of Sunshine
    The amount of time sunlight was detected at a given point.



    Same as Civil Dusk; the time at which the sun is 6 degrees below the
    horizon in the evening. At this time objects are distinguishable but
    there is no longer enough light to perform any outdoor activities.

    Dust Devil
    A small, rapidly rotating wind that is made visible by the dust, dirt
    or debris it picks up. Also called a whirlwind, it develops best on
    clear, dry, hot afternoons.

    Dust Plume
    A non-rotating "cloud" of dust raised by straight-line winds. Often
    seen in a microburst or behind a gust front.

    Dust Storm
    A severe weather condition characterized by strong winds and dust-filled
    air over an extensive area.

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


    Downward Vertical Velocity (sinking air)

    Downdraft - 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.


    Dew Point - A measure of atmospheric moisture. It is the temperature to
    which air must be cooled in order to reach saturation (assuming air
    pressure and moisture content are constant).

    Dynamic Ice
    In hydrologic terms, pressure due to a moving ice cover or drifting ice. Pressure occuring at movement of first contact termed Ice Impact

    Dynamic Lifting
    The forced uplifting of air from various atmospheric processes, such as
    weather fronts, and cyclones.

    Dynamic Wave Routing Model (DWOPER)
    A computerized hydraulic routing program whose algorithms incorporate
    the complete one-dimensional equations of unsteady flow.

    Generally, any forces that produce motion or effect change. In
    operational meteorology, dynamics usually refer specifically to those
    forces that produce vertical motion in the atmosphere.

    --- SBBSecho 3.11-Win32
    * Origin: The Thunderbolt BBS - tbolt.synchro.net (57:57/10)