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V Notch - a distinct feature in the radar reflectivity field, seen as a V-shaped notch in the downwind part of a thunderstorm echo. The V-notch 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.

VAD (Velocity Azimuth Display) - a radar display on which the mean radial velocity is plotted as a function of azimuth

Vapor - a substance in a gaseous state at a temperature below that necessary for condensation to occur (i.e., the boiling point)

Vapor Pressure - in meteorology, the pressure exerted only by molecules of water vapor in the air

Vault - same as BWER

VCP - an acronym for Volume Coverage Pattern. The VCP is the sequence of elevation angles that a NEXRAD radar is programmed to use to scan the atmosphere. The NEXRAD operator can choose to scan using one of four possible VCPs.

Veering Winds - 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.

Velocity Folding - a limitation of pulsed Doppler radar that occurs when the actual target velocity exceeds the maximum unambiguous velocity (or Nyquist velocity) that can be measured by the radar. When velocity folding occurs, for example, a large negative velocity would appear as a large positive velocity.

Vernal Equinox - the equinox when the sun approaches the Northern Hemisphere; typically called the first day of spring

Vertical Motion - in meteorology, refers to air moving upward or downward; vertical motion is important in determining if clouds will form

Vertical Visibility - the distance that an observer can see vertically into a surface-based obscuring phenomenon, such as fog, rain, or snow

Vertically Integrated Liquid - the total liquid water equivalent throughout a vertical column of radar reflectivities. VIL is computed using an empirical equation by assuming that all the reflectivity values are from liquid water. VIL has been shown to be seasonally and geographically dependent upon hail size.

Viewing Angle - the angle that the radar uses to sample a given storm. Certain features of a storm may be invisible to a certain radar (they may be aligned along a radial) but be clearly visible by a second radar. In addition, the viewing angle of the radar is important in velocity interpretation. A wind blowing perpendicular to a radial results in zero radial velocity.

VIL - an acronym for Vertically Integrated Liquid

VIP (Video Integrator and Processor) - software which contours radar reflectivity (in dBZ) into six levels:

Level 1
18 - 30 dBZ

Light precipitation

Level 2
30 - 38 dBZ

Light to moderate rain

Level 3
38 - 44 dBZ

Moderate to heavy rain

Level 4
44 - 50 dBZ

Heavy rain

Level 5
50 - 57 dBZ

Very heavy rain; hail possible

Level 6
>57 dBZ

Very heavy rain and hail; large hail possible

Virga - water or ice particles falling from a cloud but evaporating before reaching the earth's surface

Visibility - the greatest distance toward the horizon that prominent objects can be identified visually with the naked eye

Visible Radiation - the type of electromagnetic radiation that the human eye can detect

Volume Scan - a radar scanning strategy in which sweeps are made at successive antenna elevations (i.e., a tilt sequence), and then combined to obtain the three-dimensional structure of the echoes

Vort Max - short for vorticity maximum; a maximum in the vorticity field of a fluid

Vorticity - a measure of the local rotation in a fluid flow. In weather analysis and forecasting, it usually refers to the vertical component of rotation (i.e., rotation about a vertical axis) and is used most often in reference to synoptic scale or mesoscale weather systems. By convention, positive values indicate cyclonic rotation.


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