Subj : Wx Terms (D)(2) To : All From : Daryl Stout Date : Sun Nov 05 2017 12:04 am DEP Departure 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. Depression 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. Derecho (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. Desertification 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. Detritus 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. Dew 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". DEWP On a buoy report, the dewpoint temperature taken at the same height as the air temperature measurement. DFUS Diffuse Diabatic 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. Difluence (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. DIR 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). --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .