NWS Radar Images: Reflectivity

Base reflectivity image in precipitation mode
When ever you view a radar image is is most likely a reflectivity image whether you see it on television or an Internet web page or a smart phone. Reflectivity images are the 'meat-n-potatoes' of the radar. And, as they sound, they paint a picture of the weather from the energy reflected back to the radar.

The NWS Doppler radar displays reflectivity in two types: Base (½° elevation) reflectivity and Composite reflectivity. Base Reflectivity is the default image. Taken from the lowest (½° elevation) slice, it is primary used to "see what's out there".

Base Reflectivity

There are two versions of Base Reflectivity image; the short range version which extends out to 124 nautical miles (143 statute miles/230 kilometers) and the long range version which extends out to 248 nautical miles (285 statute miles/460 kilometers).

Composite reflectivity image in precipitation mode - click to enlargeThis image is available upon completion of the ½° elevation scan during each volume scan.

Composite Reflectivity

Composite Reflectivity images utilize all elevation scans during each volume scan to create the image. It is composed of the greatest echo intensity (reflectivity) from any elevation angle seen from the radar. It is used to reveal the highest reflectivity in all echoes.

Another advantage of Composite Reflectivity is in mountainous regions. Often, the Base Reflectivity ½° elevation scan is not high enough to see over mountains. With the addition of higher elevations scans, weather information over mountain peaks can be seen. View a sample composite reflectivity image.