Winter weather often brings various forms of precipitation, each with unique characteristics. Among these, freezing rain and sleet are frequently confused, yet they form under distinct atmospheric conditions. Understanding the differences between these two types of precipitation helps clarify why their impacts on daily life can vary significantly.
How Freezing Rain Forms
Freezing rain begins high in the atmosphere as snow. As these snowflakes descend, they encounter a layer of warm air, typically located several hundred to a few thousand feet above the ground, where temperatures are above 0°C. In this warm layer, the snowflakes completely melt, transforming into raindrops. These raindrops continue to fall towards the Earth’s surface.
Below this warm layer, a shallow layer of sub-freezing air exists, extending from the ground upwards. This cold layer is not deep enough for the raindrops to refreeze into ice pellets before they reach the ground. Instead, the liquid raindrops remain supercooled, meaning their temperature drops below 0°C but they do not solidify. Upon striking any surface that is at or below freezing, such as roads, trees, or power lines, these supercooled raindrops instantly freeze. This rapid freezing creates a smooth, clear coating of ice, often referred to as a glaze.
How Sleet Forms
Sleet, also known as ice pellets, originates as snow high in the atmosphere. Similar to freezing rain, these snowflakes fall into a layer of air where temperatures are above 0°C, causing them to melt into raindrops. The difference for sleet formation lies in the subsequent atmospheric layers.
After melting, these raindrops fall through a much deeper layer of sub-freezing air, which extends from the ground upwards for a considerable distance. This deep, cold layer provides sufficient time for the melted raindrops to refreeze completely before reaching the Earth’s surface. As they refreeze, they form small, translucent ice pellets. When these ice pellets strike the ground, they produce a distinct rattling sound and bounce, unlike the silent accumulation of freezing rain.
Differences
The distinction between freezing rain and sleet lies in the temperature profile of the atmosphere, particularly the depth of the freezing layer near the ground. Freezing rain forms when a thin layer of sub-freezing air is present at the surface, allowing supercooled raindrops to freeze on impact. This results in a clear, often heavy, ice glaze that coats all exposed surfaces.
Sleet, in contrast, requires a substantial, deep layer of freezing air close to the ground. This allows the melted raindrops sufficient time to refreeze into solid ice pellets while still in the air. Upon reaching the ground, sleet bounces and makes a distinct sound, unlike freezing rain which adheres silently. While both can create hazardous conditions, freezing rain typically causes more widespread power outages and travel disruptions due to the accumulating weight of ice on infrastructure and surfaces.