High Quality Content by WIKIPEDIA articles! The Bergeron–Findeisen process (after Tor Bergeron and W. Findeisen), also known as the cold rain or ice crystal process, is the formation of precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth. The equilibrium vapor pressure over water is greater than the saturation vapor pressure over ice, at the same temperature. Therefore in a mixed phase cloud, the liquid water will be out of vapor pressure equilibrium and will evaporate to reach equilibrium. The water droplets will move toward the lower pressure over the ice and diffuse onto the ice crystals. The vapor will be condensed and freeze onto the ice crystal, causing it to grow larger.