This is a special setting of the radar that gives it enhanced sensitivity that often picks up things in the atmosphere you wouldn't normally be able to spot on radar, like dust clouds, flocks of birds, temperature inversions, and also "ground clutter" from reflections off terrain and buildings in the area. 

For example, this scan at left shows the Phoenix, AZ NEXRAD in Clear Air Mode. Note how it picks up the many buildings near Phoenix at the center and also some echoes up to the NW and NE that are mountains. 

Clear Air Mode images are almost always characterized by having lots of bright colors in the image that appear in random patterns. 

DTD detects Clear Air Mode and displays it in the indicator at the top of the DTD program window. 

When in Clear Air Mode, DTD's Storm Alert functions are DISABLED to prevent false alarms.

 See our FAQ on this subject for more info

When rain, snow, or thunderstorms are detected in the NEXRAD radar scan area, the radar will switch to Precipitation Mode. In this mode, the radar's sensitivity is reduced, so that ground clutter and other objects don't interfere with the imaging of the precipitation. 

Precipitation Mode images are almost always characterized by having lots of lower level green  colors in the image that appear in wide patterns. Often you'll see "cells" of color in yellows, oranges, and reds embedded in the wide green areas, or sometimes all by themselves. These are likely to be thunderstorms. 

For example, this scan at left shows the Sacramento, CA NEXRAD in Precip Mode. Note how shows wide areas of precipitation in green and also some storm echoes up to the Northeast and Southeast that are in the Sierra Nevada mountains near Lake Tahoe. 

DTD detects Precipitation Mode and displays it in the indicator at the top of the DTD program window. 

When in Precip Mode, DTD's Storm Alert functions are FULLY ENABLED.