THIN LINE ECHOA narrow, elongated non-
precipitating echo usually associated with
thunderstorm outflow, fronts, or other density
discontinuities. Also called a fine line.
THRESHOLD VALUEAn adaptable parameter
which serves as a minimum or maximum value
that phenomena must or must not exceed to be
accepted by an algorithm or displayed on a
TIROSTelevision InfraRed Operational Satellite.
UHFUltra high frequency. (300 MHz to 3 GHz.)
VASVertical Atmospheric Sounder.
VEERINGA change in the wind direction in a
clockwise manner in the Northern Hemisphere, or
a counterclockwise manner in the Southern
VELOCITY ALIASINGAmbiguous detection
and display of radial velocities.
VHFVery high frequency. (30 MHz to 300 MHz.)
VOLUME COVERAGE PATTERNA vol-
umetric sampling procedure. A combination of
elevation slices designed to provide radar
coverage over a specific volume of the
VOLUME SCANThe completion of a sequence of
360° scans at prescribed elevation angles to obtain
a three-dimensional view around the radar site.
VOLUMETRIC PRODUCTAny product the
WSR-88D produces which requires data from the
entire volume coverage pattern before processing
can be completed.
VORTEX In its most general use, any flow
possessing vorticity. More often the term refers to
converging flow producing rotation. A tornado is a
WATER VAPOR IMAGEA satellite image
derived from the thermal energy emitted by water
vapor, usually at the 6.7 micrometerwavelength.
WEAK ECHO REGION (WER)Within a
convective echo, a localized minimum of
equivalent reflectivity associated with a strong
WEFAXAn acronym for weather facsimile,
specifically the NWS service providing satellite
imagery and graphic products via a geostationary
satellite data broadcast.