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General Reflectivity Principles

How reflectivity effects Radar Returns

Wet precipitation particles reflect better than dry precipitation particles, and the larger the wet particle, the more reflective it becomes (see Fig. 1). Wet hail, large rain droplets, and wet snow are all highly reflective, and are most likely to be found at the melting level of a thunderstorm cell, which provides maximum reflectivity (see Fig. 2). For this reason, the highest reflectivity is at temperatures above 0° C.

When initially pointing the center of the beam using tilt and range management, point the radar beam close to the freezing level, which in the United States will generally be somewhere between 7,000 to 15,000 ft. MSL. This will be dependent upon location, time of year, and other factors. At temperatures below 0° C, a thunderstorm cell will have moderate reflectivity (see Fig. 2), which diminishes when temperatures in the cell fall below -20° C.

While super cooled water droplets can be found at temperatures as low as -40° C, radar echo tops typically do not rise above FL230. Above this level in thunderstorm cells, precipitation mostly consists of frozen particles, which have the least reflectivity, and may include significant hazards such as hail.

DO NOT OVERFLY RADAR ECHO TOPS. Radar echo tops do not indicate the top of thunderstorm activity. Extreme turbulence and hail is likely to exist in the region above the radar echo tops of a cell, and turbulence bow waves are likely in clear air above a cell (see Fig. 2).