Refer to figures.

AIRBORNE WEATHER RADAR

Airborne weather radar is designed for avoiding severe weather, not for penetrating it. It detects drops of precipitation (such as rain/snow/hail). Therefore, do not try to use it to avoid instrument weather associated with clouds and fog – it does not provide any assurance of avoiding IFR weather conditions.

A knowledge of the radar principle is paramount in order to accurately tune this system and interpret the weather radar display correctly.

Reflectivity

Weather detection is based on the reflectivity of water droplets. The weather echo appears on the Navigation Display (ND) with a color scale that goes from red (high reflectivity) to green (low reflectivity).
The weather radar echo returns vary in intensity as a function of the droplet size, composition and quantity. For example, a water particle is five times more reflective than an ice particle of the same size.