Snow. Sleet. Freezing rain.
A winter storm can bring a sloppy mix of the three, pile up with pure snow, or freeze everything in thick ice. What determines which type of wintry precipitation will fall? It all comes down to temperature.
In the winter months, most precipitation begins as snow high up in the atmosphere. With below freezing temperatures all the way from the cloud to ground, precipitation continues to fall as snow, blanketing the ground in a winter wonderland.
But when warm air works its way in, things begin to change. The depth of this warm layer of air determines what type of precipitation will fall.
When a thin layer of warm air cuts through the atmosphere, the snow only briefly melts. With cold air still near the ground, it can re-freeze into ice pellets. This process creates sleet. Sleet accumulates like snow, but is extremely dense and can be difficult to plow and shovel.
When a thicker layer of warm air moves in, the snow melts and stays in liquid form longer. With a thin layer of freezing air still near the ground – the liquid freezes on surface contact, forming a glaze of ice on everything it touches. Accumulated ice can weigh down trees and utility lines, causing widespread power outages.
Finally, if the atmosphere is above freezing all the way to the ground, the precipitation falls as plain rain.
Whether a winter storm brings an icy mess or a snowy scene, it all comes down to small yet consequential variations in the atmosphere.
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