The WSR-88D calculates atmospheric motion
based on cloud and precipitation movements. It can sense motion
directed toward and away from the radar, i.e., radial velocity.
Two types of velocity data are available, including base velocity and
storm-relative velocity map (SRM) data which is calculated by subtracting out storm motion.
Thus, SRM winds are the winds
"felt" by precipitation entities as they move through
the environment. For more information, consult "Overview
of the WSR-88D Radar System." SRM data is very useful
for detecting rotation within severe thunderstorms. The figure
at left shows an SRM image over Daviess County in Kentucky. Red (green)
colors are radial winds directed away from (toward) the radar
site (not shown, but located east/right of the image area). The bright red
colors indicate strong storm-relative inflow associated with a severe
thunderstorm complex and directed into a mesocyclone (circled red/green
cyclonic circulation couplet) that produced an F3 tornado in Owensboro,
Kentucky on January 3, 2000.