Temperature inversion is needed for the melting process to occur to produce freezing rain.
Point D ่ snow
Point A ่ rain
Point B &C ่ have inversion layers
Point B ่ snow melt in the deep warm inversion layer, supercooled in the near-surface subfreezing layer, and produces freezing rain when it hit the surface.
Point C ่ snow wont melt completely in the shallow inversion layer, refreeze in
the near-surface
layer, and becomes sleet (frozon rain droplets) on the surface.