During the winter, there are 4 major precipitation types that meteorologists focus on. They are rain, freezing rain, sleet, and of course snow.
One of the difficult tasks for a forecaster is trying to figure out what type of precipitation is going to occur in the winter. An important piece of the puzzle involves determining the temperature throughout the troposphere (basically the lower 7-8 miles of the atmosphere) where the temperature usually decreases with height. However there are times when the temperature actually increases with height in the lower troposphere and this can cause problems for the forecaster.
Precipitation begins as snow and if it doesn’t encounter any layers of air that are above freezing before reaching the ground, it will fall to the surface in the form of snow.
If the snowflakes encounter a shallow layer of warm, above freezing air with below freezing air through the rest of the column, then it will partially melt and refreeze into a sleet pellet before reaching the ground.
If the snow falls into a deep layer of above freezing air with only a shallow layer of below freezing air located at the surface, (which is often the case with cold air damming,) then the liquid droplets will freeze on contact with any objects (such as trees, power lines, and roads) at the surface that are below freezing.
If precipitation falls through a large depth of the atmosphere frozen but encounters a relatively deep layer of above freezing air at the surface, then the frozen precipitation may completely melt and have no opportunity to refreeze. Thus, what traveled almost the entire trip to the ground as snow may end up falling as a cold rain instead of anything frozen or freezing!