Radar measures reflectivity. Reflectivitiy is proportional to the diamater of the partical to the sixth power dbz~(D)^6.
Snow and rain reflect different amounts of radiation. This causes problems to decide how much it is actually raining or snowing.
Melting snow can be very deceiving. When snow starts to melt it gets a watery shell around the flakes. To a radar beam it looks like a 10 cm rain drop.
Often this phenomenon is evident on radar in what is called a "bright band" where the radar shows a high echo but there are actually less rain that is thought to be there.