Freezing rain and snow are fundamentally different forms of winter precipitation. Snow consists of frozen, crystalline water throughout its descent until it reaches the surface. Freezing rain, conversely, falls as liquid water that has been cooled below the freezing point (supercooled) before it makes contact with objects on the ground.
The Physical State Difference
The defining characteristic separating these two phenomena is the physical state of the water upon impact. Snowflakes are solid ice crystals that remain frozen from the cloud layer to the ground, accumulating as a soft layer. Freezing rain is still in the liquid phase when it strikes surfaces like pavement, trees, or power lines.
This supercooled liquid instantly freezes into a dense, transparent coating known as glaze ice, which can rapidly accumulate and cause significant disruption. The transformation from liquid to solid occurs only after the droplet adheres to a surface that is at or below 32 degrees Fahrenheit (0 degrees Celsius).
The Atmospheric Recipe for Snow
For snow to fall and accumulate, the atmospheric temperature profile must be straightforward. The entire column of air, from the cloud base down to the surface, needs to remain at or below the freezing point. This continuous cold environment ensures that ice crystals formed high in the clouds do not melt during their descent.
The formation process involves water vapor depositing directly onto ice nuclei to form snow crystals. Even if the ground temperature is slightly above freezing, the precipitation remains snow as long as the air temperature throughout the rest of the atmosphere is cold enough.
The Critical Warm Layer: Freezing Rain Formation
Freezing rain requires a complex, layered atmospheric structure known as a temperature inversion. The process begins with precipitation forming as snow or ice crystals in the cold, upper atmosphere. As these crystals fall, they encounter a deep layer of air aloft where the temperature rises above freezing.
This elevated warm layer completely melts the solid ice crystals, turning them into liquid raindrops. The drops continue their descent until they reach a shallow layer of sub-freezing air trapped right at the Earth’s surface. This cold surface layer is the final and critical component.
The layer is too thin for the melted raindrops to fully refreeze into a solid ice pellet before impact. The liquid drops cool below 32 degrees Fahrenheit, entering the supercooled state while remaining liquid. This setup results in liquid precipitation that instantly glazes surfaces.
Why Sleet Is Not Freezing Rain
The key difference between freezing rain and sleet lies entirely in the depth of the sub-freezing air layer near the ground. Sleet forms through the same initial process: snow melts completely within an elevated warm layer.
For sleet, however, the cold air layer at the surface is sufficiently deep to allow the supercooled raindrops to fully refreeze before they reach the ground. This refreezing creates small, hard ice pellets.
When sleet strikes a surface, it typically bounces or rattles, unlike the silent adherence of freezing rain. Since the pellets are already solid upon impact, they prevent the formation of the smooth, uniform glaze of ice that makes surfaces treacherous.