A radar reflectivity signature seen as a V-shaped notch in the downwind part of a thunderstorm echo. The V-notch often is seen on supercells, and is thought to be a sign of diverging flow around the main storm updraft (and hence a very strong updraft). This term should not be confused with inflow notch or with enhanced V, although the latter is believed to form by a similar process.
- Browse Related Terms: Bear's Cage, Bounded Weak Echo Region (BWER), BWER, EXTD, Feeder Bands, Inflow Notch, overhang, V Notch, VIP, WER, WK
Velocity Azimuth Display
- Browse Related Terms: BASE DATA, BASE PRODUCTS, Base Reflectivity, Layer Composite Reflectivity Average, Layer Composite Reflectivity Maximum, OBSC, Radar Range, Range, Reflectivity Cross Section, Severe Weather Analysis, Spectrum Width Cross Section, Storm Relative Mean Radial Velocity Map, Storm Relative Mean Radial Velocity Regi, Storm Tracking Information, VAD, Weak Echo Region
A radar plot of horizontal winds, derived from VAD data, as a function of height above a Doppler Radar. The display is plotted with height as the vertical axis and time as the horizontal axis (a so-called time-height display), which then depicts the change in wind with time at various heights. This display is useful for observing local changes in vertical wind shear, such as backing of low-level winds, increases in speed shear, and development or evolution of nearby jet streams (including low-level jets). This product often is referred to erroneously as a VAD.
- Browse Related Terms: ADPC, Correlated Shear, Deformation Zone, FNTLYS, Frontogenesis, Helicity, Jet Wind Speed Profile, LLWS, Microburst, Mixing Depth, Mountainado, Profiler, Shear, Speed Shear, Storm Relative, Straight-Line Hodograph, Tornado Vortex Signature, VAD Wind Profile, VWP, Wind Shear, Wind Shear Profile
The locus of points just above the water table where soil pores may either contain air or water. This is also called the zone of aeration
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An air pollution transport and diffusion model developed to determine pesticide drift from aerial spraying operations in valleys.
- Browse Related Terms: AGDISP, Box Model, Chemistry Model, Diagnostic Model, domain, Full-Physics Numerical Model, Gaussian Plume Model, Gaussian Puff Model, Perturbation Model, Phenomenological Model, VALDRIFT
The period of time during which a forecast or warning, until it is updated or superseded by a new forecast issuance, is in effect.
- Browse Related Terms: 1-2-3 Rule, AGFS, Complex Gale/Storm, CWFA, Developing Gale/Storm, FA, FCST, FOUS, Grids, High Seas Forecast, Marine Zone, NSSFC, OFSHR, PROGGED, Radar Meteorology, RAFC, RAFS, Red Flag Warning, TAF, Valid Time, ZFP
(VTEC) - The Valid Time Event Code (VTEC) always is used in conjunction with, and provides supplementary information to, the Universal Geographic Code (UGC), to further aid in the automated delivery of National Weather Service text products to users. The VTEC is included in many event driven or non-routine products and in some routine Marine forecasts. The VTEC provides information on the event, while the UGC describes the affected geographic area.
- Browse Related Terms: AFOS, AFSS, SYNS, UGC, Universal Geographic Code, Valid Time Event Code, VTEC
The reduction in volume of a valley (or basin) as compared to an equal depth volume with a horizontal floor. Because the valley volume is smaller, equivalent heat fluxes will cause larger changes in temperature in the valley volume than in the flat-floor volume.
- Browse Related Terms: absorption, attenuation, Emissivity, Entropy, Fluence, Longwave Radiation, Ozone, Radiance, Sub-synoptic Low, TKE, Valley Volume Effect
In hydrologic terms, a device fitted to a pipeline or orifice in which the closure member is either rotated or moved in some way as to control or stop flow.
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The partial pressure of water vapor in an air-water system.
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Same as Variable Wind Direction; a condition when
(1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or
(2) the direction is variable and the wind speed is less than 6 knots.
- Browse Related Terms: g, Gust, Kts, MAX, Peak Wind Speed, PK, Rain Shield, Squall, Turbulence, Unimodal, Variable Wind, Variable Wind Direction, Wind Gust, Wind Shift, Wind Speed
A condition when
(1) the wind direction fluctuates by 60° or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or
(2) the direction is variable and the wind speed is less than 6 knots.
- Browse Related Terms: g, Gust, Kts, MAX, Peak Wind Speed, PK, Rain Shield, Squall, Turbulence, Unimodal, Variable Wind, Variable Wind Direction, Wind Gust, Wind Shift, Wind Speed
A measure of variability.
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Vicinity
- Browse Related Terms: ENHNCD, INVOF, Major Flare, Proton Flare, VCNTY
Volume Coverage Pattern - A volumetric sampling procedure designed for the surveillance of one or more particular meteorological phenomena. Clear Air Mode uses VCP 31 and 32. Each has a Volume Scan consisting of 5 elevation angles (0.5 to 4.5 degrees) in ten minutes. VCP 31 has a long pulse length and provides a better signal-to-noise ratio permitting lower reflectivity returns to be detected. VCP 32 has a short pulse length which provides for larger unambiguous velocity values. Precipitation Mode uses VCP 11 and 21. VCP 11 provides better vertical sampling of weather echoes near the antenna and is usually preferred in situations where convective precipitation is within 60 nmi of the antenna. VCP 11 Volume Scan consists of 14 elevation angles (0.5 to 19.5 degrees) in 5 minutes. VCP 21 has a slower antenna rotation rate and provides better velocity and spectrum width estimates beyond 60 nmi. VCP 21 Volume Scan consists of 9 elevation angles (0.5 to 19.5 degrees) in 6 minutes.
- Browse Related Terms: Echo Tops, ENTR, Plan Position Indicator, PPINE, Range Height Indicator, RELBL, Sectorized Hybrid Scan, UCP, Unit Control Position, VCP, Volume Scan
A clockwise shift in wind direction (for example, south winds shifting to the west).
- Browse Related Terms: Backing, BCKG, Plume Impingement, Sea Breeze Front, SHFT, Veering, WSHFT
Winds which shift in a clockwise direction with time at a given location (e.g., from southerly to westerly), or which change direction in a clockwise sense with height (e.g., southeasterly at the surface turning to southwesterly aloft). The latter example is a form of directional shear which is important for tornado formation. Compare with backing winds.
- Browse Related Terms: Backing Winds, Directional Shear, SELY, SLY, SWLY, Veering Winds, VR, Wind Shift Line
A WSR 88-D product which shows the radar derived wind speeds at various heights. This radar product shows the wind speeds from 2,000 to 55,000 feet above the ground. VAD and EVAD (Extended VAD) are methods of guessing the large scale two-dimensional winds from one-dimensional radial velocity data. They are essentially multivariate regressions which fit a simple, large scale wind model to the observed winds. EVAD also estimates the large scale horizontal divergence and particle fall speed. See VWP.
- Browse Related Terms: Couplet, FNTGNS, Rankine Vortex, Spectrum Width, Triple Doppler, Velocity Azimuth Display, Velocity Cross Section, VLCTY, Volume Velocity Processing, VVP