Rain, sleet or snow? Why winter storms can be so confusing
A quick guide to winter precipitation types
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Winter precipitation can take several forms within a single storm system — which is why these storms can be so confusing. Rain can change to sleet and sleet can resemble snow. In some cases, precipitation begins as snow, melts into rain as it falls through a layer of warmer air, and then either refreezes or remains liquid before reaching the ground.
Subtle temperature differences in the atmosphere drive these changes, and even the smallest variations can determine whether precipitation reaches the ground as rain, sleet, snow or freezing rain.
Snow
Snow is the most common type of wintry precipitation that forms in clouds cold enough to create snowflakes. Snowflakes are simply clusters of ice crystals that form and fall from a cloud.
For a snowflake to remain intact, it must fall through a column of air that keeps it below freezing.
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If warmer air moves into the air column, the snowflake will melt and may transform into freezing rain or sleet.
Both freezing rain and sleet occur when snowflakes pass through a layer of warm air. The key difference between the two lies in the thickness of the layer of freezing air below the warm air.
Freezing rain
Freezing rain occurs when snowflakes fall into a thicker layer of warm air and melt completely.
When temperatures near the surface are at or below freezing, the raindrops freeze instantly upon contact, forming a layer of ice. Even light amounts of freezing rain can create a thin glaze of ice on the ground, trees and power lines, leading to hazardous conditions.
Sleet
When falling snowflakes pass through a shallow layer of warm air, they partially melt. These partially melted drops then refreeze as they pass through a layer of freezing air just above the surface, forming hard, frozen raindrops known as sleet or ice pellets.
Understanding these differences makes it easier to see why winter storms can feel unpredictable, and why what falls from the sky can change so quickly.
