The winter can bring many threats to travel and basic day-to-day activities. These include frigid cold, icy roadways, and of course snow.
But there are other precipitation types besides snow - terms you may have heard of but never really understood what they meant.
There are times when the forecast will fall for a chance of sleet. Or maybe freezing rain is expected.
What exactly are these different types of precipitation?
The most basic types of precipitation to understand are rain and snow. But first, let's understand how precipitation forms. Precipitation forms when water vapor condenses in the clouds. Once it gets too heavy - saturated - for the clouds to hold the moisture, it falls as rain.
The type of precipitation that falls to the ground depends on the temperatures.
If temperatures remain above 32 degrees both in the sky above and on the ground, it will be rain. That is, the precipitation is entirely liquid, and doesn't freeze.
Though this isn't really a type of wintry precipitation, if temperatures fall soon afterwards below freezing, it could cause ice.
Snow occurs when the air aloft through several thousand feet above are below freezing. Water droplets become crystals, and fall as snow.
Rain could actually start as snow several thousand feet up but melt completely on the way down, and therefore is rain.
Now for the harder types.
Sometimes there is a very cold layer of air both way above at several thousand feet above, and also in the lowest parts of the atmosphere. But in the middle, a small layer of warm air above 32 degrees remains.
When this happens, the snow crystals will melt somewhat on their way through this warm layer. But as it gets even lower, it refreezes.
The droplets generally come down looking like pellets.
Typically, sleet will accumulate in a thick pack, and it can be very difficult to shovel or plow.
Freezing rain will occur when there is plenty of warm air throughout the atmosphere. This keeps the precipitation as rain.
But the ground, and other surfaces, are still below freezing (typically after a few days of below-freezing temperatures have occurred). Therefore, the rain freezes on contact with these surfaces.
This can create very hazardous travel conditions, since roads and sidewalks can turn icy quickly.
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