Snow, freezing rain and sleet: A wintry precipitation primer

When the forecast calls for anything other than rain or snow, it can cause some panic or anxiety. While terms like freezing rain and sleet may prompt extra precautions, understanding how these types of precipitation form can help alleviate concerns.

As a meteorologist, it is crucial to understand the thermal (temperature) profile above us to accurately predict the types of precipitation a weather system will bring. Precipitation forms in the troposphere, the layer of the atmosphere where we live, but it originates high above us.

Here’s a quick primer on snow, freezing rain and sleet.

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.

During the winter, 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.

No matter the type of precipitation, it's always important to stay tuned to the forecast to remain safe and informed.