Apart from a few memorable events, we don’t get much winter weather here in the Lowcountry.
There’s the snow back in 2018, and the historic, and only White Christmas in Charleston after Hugo in 1989. Then there’s our ice storms, which just cause headaches! Predicting what will fall: snow, ice, or just plain rain can also be a headache.
In my opinion, it can be one of the most difficult weather forecasts to make as a lot of variables have to be considered- the most important of which are the temperatures at different levels of the atmosphere. Weather balloons are the main way to measure this, taking readings from the surface to nearly 100,000 feet! From that data, meteorologists can visualize what the vertical slice of the atmosphere looks like through a diagram called a Skew-T.
I could explain what each type of winter precipitation looks like on a Skew-T, but as the saying goes- cookies make everything, including explaining science, better.
Consider different variants of sandwich cookies, each representing a different type of winter precipitation. The only difference between them is the amount of icing, symbolizing the amount of warm air in the atmosphere. More icing- a bigger layer of above freezing temperatures above the ground and below the clouds.
Let’s start here. If there’s a lot of that warm air, snowflakes will melt and fall as liquid rain all the way down- that’s this Double Stuf, there isn’t any part below freezing, so we’ll get just cold rain! It gets a bit more complicated when we add a layer of below freezing temperatures but still keep a solid chunk of warm air.
That’s this regular oreo, or freezing rain. Snow melts and falls as rain most of the trip down- but encounters a pool of cold air near the surface, cooling it down, but not long enough for it to freeze until it lands and instantly freezes on surfaces- like power lines, roads, and tree limbs! We don’t want this!
But if that wedge of warm air high up in the atmosphere is even shallower, let’s say this Oreo Thin, there’s more time for the melted snow to re-freeze into ice pellets, or sleet. It’s similar to what happens during freezing rain, but easier to handle as ice pellets bounce off of tree limbs and power lines. It’s still not snow as even though there’s a lot of cold air, that pesky thin layer of warm air is still present.
To see the fluffy stuff, we have to make sure there’s no warm air at all between the snow that’s falling and the surface. That would be a Oreo with no icing! Snowflakes fall, never encountering any warm air, and will stay in ice form all the way to the surface.
These are the possible outcomes in a winter storm- figuring out which one we could see is the tricky part as small changes in temperature can make a huge difference. If I had to choose, I’d take the Mega Stuff, but no matter what, you can count on us to tell you what cookie to expect the next time a winter system eyes the Lowcountry.
Storm Team 2 Meteorologist David Dickson