We all associate snow, sleet, hail, and freezing rain with wintry and stormy conditions. Before every big winter storm, weather forecasters outline the variety of potential precipitation that citizens could potentially encounter and yet, the specifics of these water-based threats are rarely ever explained. So how exactly do these types of precipitation form and what’s the difference between them?
Here at Arkansas Weather, we will be the first to tell you that forecasting winter weather is a tricky thing to do, and people do not like when meteorologists get it wrong! So, rather than trying to be pretentious in trying to explain each type of precipitation, I am just going to define them all based on the rulings of the American Meteorological Society Glossary of Meteorology, and explain what separates them from one another.
Snow is precipitation composed of white or translucent ice crystals, chiefly in the form of snowflakes. It originates in clouds when temperatures are below the freezing point and water vapor in the atmosphere condenses directly into ice without going through the liquid stage. Once an ice crystal has formed, it absorbs and freezes additional water vapor from the surrounding air, growing into a snow crystal or snow pellet, which then falls to Earth.
Sleet is a mixture of rain and snow and is also known as ice pellets. Sleet forms in stratus clouds when snowflakes start to melt as they fall from the cloud. As they fall through sub-freezing air they refreeze into grain like particles. Ice pellets are smaller than hail stones and will bounce when they hit the ground.
Hail is a shower of round or irregularly shaped pieces of ice that form inside a cumulonimbus cloud. They start off as small ice particles or frozen raindrops that are caught in the updraft of air inside the cloud. As they rise they grow by gathering water on their surface. How big they grow depends on how strong and extensive the updraft is and how much water is in the cloud. In energetic clouds the hailstones may go up and down a number of times, adding a layer of ice each time. Eventually they become so heavy that they can no longer be supported by the updraft and will fall to the ground.
Freezing rain is rain that falls when surface temperatures are below freezing and the liquid precipitation freezes when it hits the super-cold surface. Unlike sleet or hail, freezing rain is made entirely of liquid droplets. The raindrops become super-cooled while passing through a sub-freezing layer of air and then freeze upon impact with any surface they encounter, including the ground, trees, electrical wires, and automobiles.
So next time you’re stuck in a hailstorm or messing around in the snow, you can now understand how it was formed high above you in the clouds.
