Depending on the type of weather occurring and the area of the U.S., forecasters use a set of rainrates which are associated to the dBZ values. These values are estimates of the rainfall per hour, updated each volume scan, with rainfall accumulated over time. Hail is a good reflector of energy and will return very high dBZ values. Since hail can cause the rainfall estimates to be higher than what is actually occurring, steps are taken to prevent these high dBZ values from being converted to rainfall. Base reflectivity only shows reflected energy at a single elevation scan of the radar.
Composite reflectivity displays the highest reflectivity of ALL elevations scans.
This occurs often with severe thunderstorms. The updraft, which feeds the thunderstorm with moist air, is strong enough to keep a large amount of water aloft. Once the updraft can no longer support the weight of suspended water then the rain intensity at the surface increases as the rain falls from the cloud. These radars look better on a black background in your MSIE browser click on tools internet options then colors. Uncheck the checkmark use windows colors, click on the button beside text and pick red as the color then click on the box beside background then select black as the color click on ok to enable and now the background is black.