Snow, sleet and freezing rain. This winter we have experienced them all, but what is the science behind them?
When it comes to how precipitation falls, it all depends on the air temperature. Think of the atmosphere as sectioned into three different layers of temperature. If the first layer is below freezing, then precipitation begins as snow, and the air temperature of the layers below determines what form of precipitation will fall to the ground, either snow, sleet or freezing rain.
Snow occurs when the temperature is below freezing in every layer, causing the snow to directly fall to the ground.
Sleet occurs when there is a layer of warm air in between two layers of freezing air. When the snow falls into this middle layer, it melts and turns to water. This water then falls through the bottom layer and re-freezes before reaching the ground surface.
Freezing rain is formed the same way sleet occurs, however, with freezing rain, the layer of warm air is much thicker and when the snow melts it does not have time to re-freeze before hitting the ground. This results in the liquid water freezing on contact with the ground or any object it comes in contact with. It produces clear ice on surfaces and is also known as glaze ice.
Freezing rain, when falling for an extended time, has the potential to cause large amounts of damage due to the increased weight the forming ice can add to the object it forms on. When it forms on trees and power lines it can cause them to sag and eventually break from the increased weight.