Airborne Weather Radars (AWRs) have been created so that the pulses the emit reflect best off objects that are the same size as large water droplets hailstones. One of the primary tasks of an AWR system is to detect upcoming turbulence and bad weather, so that the pilots can take necessary precautions or avoiding action.
The largest areas of turbulence come from cumulonimbus (CB) clouds, which contain large droplets of water, ice crystals, and hail stones. Modern AWRs are set up to have a wavelength of approximately 3cm, so they bounce off these types of precipitation the most. The radars have been tuned this way to make sure that more radar returns means that there is a higher chance of turbulence in that area. Usually, the bigger the hail/droplets, the worse the turbulence.
The radar pulses will always reflect off wet hail and large water droplets better than they will off smaller water droplets, dry hail and ice crystals.
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