What determines whether precipitation will fall as freezing rain or snow?
Our atmosphere is composed of layers of air with different temperatures. So, air temperature at the earth’s surface may be different from that above. What determines whether you get freezing rain, ice pellets, snow, or rain, is the thickness of warm and cold air over your region as well as the surface air temperature. For example, freezing rain is possible when warm, moist air with temperatures above 0C is sandwiched between two colder layers of air below 0C. Precipitation from higher, colder levels begins falling as snow. As it falls through the warmer layer in between, the snow melts into raindrops. The warm layer should be over 1 km thick with temperatures above 0C in order for the snow to melt. The precipitation now enters the sub-freezing surface layer and becomes super-cooled rain (raindrops below 0C) which then freezes as it falls onto objects on the ground. If the warm layer is not deep enough to melt all the snow flakes into raindrops, partially melted snowflakes will refreeze
