The ice crystal then absorbs the water vapor, depositing it on their surface. At the same time, the loss of vapor from the water droplets causes them to shrink in size. A necessary initial requirement for this process is the presence of both condensation nuclei and deposition nuclei . Because of this phenomenon, cold clouds can contain both ice crystals and supercooled water droplets. The relative proportion of these two types of particles determines whether snow crystals grow to a size to overcome atmospheric updrafts.
Freezing rain occurs when water droplets hit a cold surface and freeze.
For this to occur a surface temperature inversion is required. In such an inversion, the surface must have a temperature below freezing, while the temperature of the atmosphere where the precipitation forms is above freezing. Surface inversions may develop from a variety of causes, but typically, they occur near the leading edge of cold air from the North as it pushes southward. Ice pellets or sleet are transparent or translucent bits of frozen water with a diameter less than 5 millimeters. To form, these pellets require an environment where raindrops develop in an atmosphere where the temperature is above freezing and then fall into a lower layer of air with temperatures below freezing.