VAD - Velocity Azimuth Display. A radar display on which mean
radial velocity is plotted as a function of azimuth. See VWP.
Vault - Same as BWER.
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. Compare with backing winds.
Vertically-stacked System - A low-pressure system, usually a
closed low or cutoff low, which is not tilted with height, i.e.,
located similarly at all levels of the atmosphere. Such systems
typically are weakening and are 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.
VIL - Vertically-Integrated Liquid water. A property computed
by RADAP II and WSR-88D units that takes into account the
three-dimensional reflectivity of an echo. The maximum VIL of a
storm is useful in determining its potential severity, especially in
terms of maximum hail size.
VIP - Video Integrator and Processor, which contours radar
reflectivity (in dBZ) into six VIP levels:
VIP 1 (Level 1, 18-30 dBZ) - Light precipitation
VIP 2 (Level 2, 30-38 dBZ) - Light to moderate rain.
VIP 3 (Level 3, 38-44 dBZ) - Moderate to heavy rain.
VIP 4 (Level 4, 44-50 dBZ) - Heavy rain
VIP 5 (Level 5, 50-57 dBZ) - Very heavy rain; hail possible.
VIP 6 (Level 6, >57 dBZ) - Very heavy rain and hail; large hail
*Virga - Streaks or wisps of precipitation falling from a cloud but
evaporating before reaching the ground. In certain cases, shafts of virga may precede a microburst; see dry microburst.
V Notch - 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.
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. Volume scans are necessary to determine thunderstorm type,
and to detect features such as WERs, BWERs, and overhang.
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
Vort Max - (Slang; short for vorticity maximum), a
maximum, in the vorticity field of a fluid.
VWP - VAD
Wind Profile. 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
This product often is referred to erroneously as a VAD.