A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

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 Wind Profile (VWP)

a radar plot of horizontal winds, derived from VAD data, as a function of height above a Doppler Radar. Height is plotted on the vertical axis and time is plotted on the horizontal axis. This display is useful for observing local changes in vertical wind shear, e.g., backing of low-level winds, increases in speed shear, and evolution of jet streams/low-level jets.


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


an attribute that may change its value while it is under observation. Examples include time, temperature, and wind speed.

Variable Wind Direction

a condition when (1) The wind direction varies by 60 degrees or more during a 2-minute evaluation period and the wind speed is greater than 6 knots (~ 7 mph), or (2) The direction is variable and the wind speed is less than 6 knots (L&V).


same as BWER




a geometric object that has both a magnitude (size) and a direction. A vector can describe where something is moving and how fast it is moving.

Veering Winds

winds that 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 (VLCTY)

the rate of change of position. It is represented by a vector, so both speed and direction are required to express velocity. A velocity example is: "10 mph from the west". Wind barbs can be used to visually represent velocity.

Velocity Azimuth Display (VAD)

a radar display on which the average radial velocity is plotted as a function of azimuth

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 (VRT MOTN)

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

Vertical Pressure Gradient Force

closely balances gravity so that all the molecules in the atmosphere are not forced into the lowest meter above the ground. This force results from molecules in the high pressure near the earth’s surface trying to move upward where the pressure is lower.

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 (VIL)

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.

Vertically Stacked System

a low-pressure system, usually a closed low or cut-off low, which is not tilted with height, i.e., located at a similar location at all levels of the atmosphere. Such systems typically are weakening and slow-moving, and are less likely to produce severe weather than tilted systems. However, cold pools aloft associated with vertically-stacked systems may enhance instability enough to produce severe weather.

Video Integrator and Processor (VIP)

software that 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

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.


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


visible/visibility or visible satellite imagery; see Visible Satellite Imagery

Visibility (VIS or VSBY)

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

Visible Satellite Imagery (VIS or VSB)

this type of satellite imagery uses reflected solar radiation to see things in the atmosphere and on the Earth’s surface. Clouds and fresh snow are excellent reflectors, so they appear white on the imagery. Clouds can be distinguished from snow, because clouds move and snow does not move. Meanwhile, the ground reflects less sunlight, so it appears black on the imagery. Since this imagery relies on reflected radiation, it cannot be used at night.


see Velocity





Volume Coverage Pattern (VCP)

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.

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

see Vorticity Maximum

Vortex (plural: vortices)

a spinning flow of fluid. A tornado is an example of a visible vortex.

Vorticity (VOT or VORT)

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 (counter-clockwise) rotation.

Vorticity Maximum (Vort Max)

a maximum in the vorticity field of a fluid. Rising motion may be found near a vort max.


see Vorticity


veer; see Veering Winds


see Vertical Motion


see Visibility