CEDAR RAPIDS, Iowa (KCRG) - From Tuesday afternoon through Thursday, all types of winter precipitation will occur across eastern Iowa. Snow and rain are the most common types, and both are very easy to explain. Freezing rain and sleet are more complicated and involve layers of warm and cold air.
Snow that falls out of the cloud and doesn’t go through a deep or warm layer of air on the way to the ground stays as snow. Meanwhile, rain happens when there’s a deep layer of above-freezing air above the ground or all the way up to the clouds.
Freezing rain occurs when a warm layer of air is present aloft, usually around 4,000 or 5,000 feet above the ground. Snow that falls into that layer melts into rain. After this point, the raindrop cannot change back into a snowflake and will fall into a shallow layer of below-freezing air near the ground. The liquid raindrop doesn’t have enough time to refreeze before hitting the ground, but turns into ice after reaching the surface.
Sleet forms in a similar way, but the warm layer may be higher up in the atmosphere, or there is simply a deeper cold layer above the ground. The raindrop has enough time to freeze into an ice pellet before reaching the ground.