Zach’s Weather Whys: Just what causes precipitation type

Digital Originals

CENTRAL ILLINOIS — Welcome to this week’s edition of Zach’s Weather Whys.

We are edging closer to that average first snowfall of the season in Central Illinois. The Historical Date of First Measurable Snowfall: November 8th, and the Average Date of First Measurable Snowfall: November 23rd.

The radar will likely have what we call ‘a mixed bag of precipitation.
There’s a few factors that go into whether or not it’s a snow fest, an icy mess or just plain ole’ rain.

Think of the atmosphere like a cake with several layers.

For snow, first and foremost, it needs to be cold enough at ground level.
The temperature high above also needs to be below freezing.

Let’s assume the air from the surface to the clouds is below freezing, well there’s that snow you’ve been wanting.
If snow falls and encounters warmer air that extends all the way to the surface, grab the umbrella cause it’s raining.

Let’s say the snow falls through a thin pocket of warm air, melts and then refreezes in another cold pocket. Little pellets of sleet will be hitting the ground.

It’s slightly different for freezing rain. If most of the atmosphere is just above freezing but a thin layer of freezing air exists at the surface. The raindrops are already very cold and easily melt on contact if the surface is freezing or below freezing.

Freezing rain makes for disastrous driving conditions by coating the road in a sheet of ice.

I don’t know about you, but I’d rather have the powdery stuff than the dreaded freezing rain.

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