May 11^th, 2003

• Used extensively to identify the location, intensity, pattern, and movement of precipitation, including light snow flurries to heavy rain and hail producing thunderstorms. Reflectivity data provide a wealth of crucial information needed to issue accurate severe weather warnings. High reflectivity values denote that heavy rain and possibly hail are occurring within thunderstorms. The radar generates reflectivity data at various altitudes, which permits an evaluation of thunderstorms in the lower, middle, and upper portions of the storms in order to determine their vertical structure. In winter storms, reflectivity data clearly can slow banded precipitation, including snow that can lead to narrow zones of heavier snowfall amounts.

• Measures winds relative to a moving precipitation entity (e.g., a thunderstorm). In other words, it is the wind that a thunderstorm actually "feels" as it moves through the environment. It is calculated by subtracting out the motion of the storm from the actual wind. Storm-relative velocity is critical for detecting shear zones and circulations/mesocyclones within severe thunderstorms that could result in damaging surface winds, hail, and even tornadoes. Converging and diverging wind fields can be detected using storm-relative data as well, which also have important implications on the structure and evolution of thunderstorms and their potential severity. To better conceptualize storm-relative velocity, consider this example: if a person rode a bike outside (i.e., was moving), the wind velocity that person felt while moving would be "storm-relative" or "system-relative" (combines the actual wind with the movement of the person), i.e., different from the actual or "ground-relative" wind.