DAX Radar
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Composite Reflectivity

When all returns from all elevation scans are compiled an image is created which takes the highest dBZ value from all elevations, called Composite Reflectivity. It is a picture of the strongest returns from all elevations. Composite Reflectivity looks at ALL elevation scans in order to create an image. When compared with Base Reflectivity, the Composite Reflectivity can reveal important storm structure features and intensity trends of storms. This is important because often during the development of strong to severe thunderstorms, rain-free areas (or areas with light rain) develop as a result of strong updrafts. Yet, because it requires all elevation scans to be completed, unlike the Base Reflectivity being the first image created, Composite Reflectivity is the last image created in each volume scan. Therein lies an important point when viewing composite reflectivity images; always check the time of the image. Often, the base reflectivity image and composite reflectivity image will not have the same time with the base reflectivity image being the most recent.

When compared with Base Reflectivity, the Composite Reflectivity can reveal important storm structure features and intensity trends of storms. This is important because often during the development of strong to severe thunderstorms, rain-free areas (or areas with light rain) develop as a result of strong updrafts. In a loop it will change to the base reflectivity image from the same time as the composite view. The first thing you will notice about the composite image is there is much more “green” color near the radar, located at the center. When higher elevation scan information is included in the composite reflectivity, it appears to indicate more widespread rain. However, the base reflectivity images does not show that rain so it is probably not reaching the ground but evaporating as it falls from very high in the atmosphere. Evidence of very strong updrafts (leading to the possibility of severe weather) can be seen.

One other note of caution, due to the time it takes to produce and transmit an image, all radar images show what HAS happened and NOT NECESSARILY WHAT IS happening.