Winter Precipitation Types

Posted: December 21, 2016, 8:57 am by nsharr
Freezing rain downs a large branch in Downingtown, PA.


During the winter, there are 4 major precipitation types that meteorologists focus on. They are rain, freezing rain, sleet, and of course snow. Generally, the precipitation type you see is dependent on the amount of above freezing air you have above the surface. If the layer is entirely warmer than 32°F you get rain and if it is entirely below freezing, you will see snow. An intruding warm layer in between is where we need to deal with these other precipitation types. If the warm layer is shallow, the snow will melt on its way down to the surface, but as the newly melted drops fall into a thick layer of cold air closer to the surface, they refreeze into ice pellets commonly known as sleet. These little balls of ice tend to bounce off many surfaces (like your car windshield) making a distinct “pinging” sound. A thicker warm layer, however, will cause the newly melted drops to remain unfrozen and will not have time to refreeze into sleet before reaching the ground. If the temperature of the surface that the drops contact is below freezing, the drops will freeze creating a layer of ice. This is known as freezing rain and it can create icing on roads, trees, buildings, electrical lines, and cars.

Image courtesy of National Weather Service

Freezing rain is especially dangerous because it can catch many off guard due to its appearance as regular rain. However, it can coat every surface that is below freezing with ice. In fact, you can even get freezing rain with an air temperature of around 35°F if the ground is cold enough. Freezing rain can quickly create very hazardous driving conditions as even a thin coating of ice can be just as treacherous as a few inches of snow. In addition, ice build-up on electrical lines can result in power outages and also bring down tree branches (as seen below in Downingtown, PA February 5th). Just remember, if you see freezing rain in the forecast, don’t take it lightly. Drive cautiously, be prepared for power outages and stay safe.

Freezing rain coats a branch with thick ice in Chester County, PA 


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