With reports of wintry weather coming — cold rain, snow, ice, and more — it’s probably left you wondering what the difference is between all that cold precipitation. Not everyone is clued into the different types of weather phenomenons that strike when the temperature falls.
When the temperature gets below freezing, it doesn’t always mean snow. We could also see freezing rain, sleet, a wintry mix, or even just plain cold rain. But if all forms of precipitation start as atmospheric water that falls to the ground, how do we end up with all these different kinds of cold weather precipitation?
Most precipitation that forms in clouds during the cold of winter starts out as snow, because it’s cold enough up there to create snowflakes. It has to be below freezing, of course. Snowflakes are really just collections of ice crystals that cling to each other as they fall down towards the ground. In order for snow to stay, well, snow, the air has to remain at 32 degrees Fahrenheit or colder. This ensures that as the snow falls through the atmosphere to reach the ground, it stays exactly as it is.
Sleet starts out the same as snow, but changes as it falls down to the ground. Snowflakes form in the atmosphere, but they partially melt when they pass through a shallow layer of warmer air. The slushy drops then refreeze as they get back to a layer of freezing air above the ground, and eventually reach the ground as frozen drops that bounce on impact. If there’s enough of it, it can accumulate on the ground like snow — but clearly, it’s not snow.
Okay, but then what’s freezing rain? This stuff follows a similar journey as sleet, except that layer of warmer air is larger. As the snowflakes hit a larger pocket of warm air in the middle of their journey, they melt. That’s the key difference here, that more warm air means it melts the snowflake completely. Of course, before it hits the ground it goes through another layer of cold air before hitting the ground. There isn’t enough time for the precipitation to refreeze before reaching the ground, but they are “supercooled.” Once the cold water droplets reach the ground, they refreeze upon contact with anything that is at or below 32 degrees Fahrenheit.
That leaves us with good ol’ rain. Even if it’s cold enough in the atmosphere to form snowflakes, it has to remain at or below freezing down here on the ground in order to see anything but rain. If the snowflakes warm up enough to melt and never refreeze, we just see wet rain.