HOUSTON — “Wintry mix” – it's a term we use to talk about the combination of several kinds of winter precipitation.
And if you've ever wondered why we sometimes see that mix rather than just snow, there are several factors.
The most important one is temperature, and you can think about it like layers in a cake.
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At the base, we're talking about surface layer temperatures. If they're at or below freezing, it can lead to snow, freezing rain, and sleet.
If the surface temp stays above freezing, you're more likely to just get rain or freezing rain.
The next layer of temperatures is just above the surface. If that layer is above freezing, that warm layer can melt any freezing precipitation as it heads toward the ground, leaving you with a combination of sleet or freezing rain.
And finally, the temperatures aloft in the cloud layer play a huge factor in what we end up seeing.
Typically, air temperatures in that upper layer must be at least 10 degrees below freezing when the precipitation process begins to create ice.
And that mix of winter precipitation can create a real mess. Sleet is tiny pellets of ice that pings off your windows when it hits. If it sticks, it'll create a crunchy, icy layer on the ground.
Freezing rain is rain that stays in liquid form until it strikes a below-freezing surface where it sticks. It can leave a glazed sheet of ice on everything from trees to cars.
And there's graupel, which is sometimes called “soft hail.” It's precipitation that forms when there are above-freezing temps at ground level but super-cooled conditions in the air.
Water droplets collect and freeze on falling snowflakes, creating very small balls of crisp, opaque ice.
All of these make up our wintery mix.