Nexrad Maps
Base Reflectivity
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Single-site NEXRAD base reflectivity data are updated every 5, 6, or 10 minutes, depending on whether the radar is in normal precipitation mode, storm precipitation mode, or clear air mode. The same NEXRAD base reflectivity information (excluding clear air mode data) is incorporated into the WSI NOWrad national and regional mosaics, except that the NOWrad images go through rigorous quality control procedures that remove most false echoes caused by ground clutter and anomalous propagation (AP). Caution must be exercised in attempting to interpret the single site NEXRAD images because they often contain 'artifacts' that are not actual precipitation echoes.

Base Reflectivity is a measure of the intensity of precipitation occurring, and is reported in units of DBZ. The WSR-88D emits pulses of energy into the atmosphere at regular intervals. When this energy impacts something (i.e. a raindrop, a snowflake, a mountain, etc.), some of the energy is scattered back to the radar dish. The amount of energy which is received back at the radar dish is measured in units of DBZ (decibels). The higher the DBZ value the larger the object. Large raindrops and hail, for example, produce high DBZ values. In general, DBZ values greater than 15 indicate areas where precipitation is reaching the ground; DBZ values less than 15 usually are an indication of very light precipitation which in most cases is evaporating in the atmosphere before it reaches the ground.

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