Winter Wonders - The Science Behind Snow and Sleet

Types of Winter Precipitation:
Freezing Rain
According to the National Severe Storms Laboratory (NSSL), freezing rain occurs when snowflakes fall into a warmer layer of air and melt into rain.
When the water hits a second layer of freezing air as its falling, it becomes cold again, but not enough to make it freeze. When the droplets hit the surface, that is when it freezes on contact if the surface is below 32 degrees Fahrenheit.
This freezing of water makes a glaze of ice that make surfaces extremely slick and dangerous to walk or drive on. The water can also freeze around trees, power lines, and other surfaces. A significant accumulation of freezing rain which lasts for several hours is called an ice storm.
Sleet
Sleet happens when snowflakes only partly melt when they enter a warm layer of air as they fall through the atmosphere to the ground. Think of sleet as it’s falling as droplets of slush.
When the slush droplets hit the second layer of freezing air, they freeze as they fall. When they hit the ground, they are considered frozen raindrops that bounce on impact.
Snow
Snow is the coldest of winter weather precipitation. This is an accumulation of ice crystals that cling together as they fall to the ground.
Snow continues to fall when the temperature remains at or below 32 degrees Fahrenheit from the base of the cloud to the ground.
There is one more term that you may have heard our abc27 weather team say and wonder what it means:
Graupel
Graupel, as defined by the NSSL, are soft small pellets formed when supercooled water droplets freeze onto a snow crystal in a process called riming. If the riming is particularly intense, the rimed snow crystal can grow to an appreciable size but remain less than 0.2 inches.
Graupel can sometimes be called snow pellets or soft hail. Usually, when handled, graupel pellets melt and disintegrate since they are not fully frozen.