My Latest Thinking on This Storm

Thursday Evening Forecast Update: My thinking on the storm is roughly the same as earlier. The only change I see is that we could see the freezing rain line dip a bit more to the south during the late morning/early afternoon on Friday. I’ll start with the forecast and then below go through all the details.

The Forecast: The first significant wave of the storm will start tonight sometime between 10pm and midnight tonight. This will all be rain because the temperatures will be too warm for anything else. The next wave arrives tomorrow morning between about 7am and 1pm. During that time we’ll have several hours of freezing rain in the Northern Midland Counties – including parts of northern Richland, Saluda, Newberry, Kershaw, and Lee Counties. This will likely cause at least some impacts on the roads before the warmer air can finally drift north and slowly change the freezing rain to rain during the afternoon. (I should point out that we will likely see some freezing rain mixed with rain in Lexington, southern Richland, Saluda, and Sumter Counties, but I don’t expect that there will be enough to cause any adverse impacts.) From there we’ll all see on and off rain from Friday afternoon to about 1am to 2am on Saturday. At that point some colder air will be filtering in from the northwest, which means we’ll see some snow showers from roughly 2am to 11am on Saturday. But there will be little accumulation because there won’t be much moisture left to work with. And by Saturday afternoon the temperatures will warm up enough that what’s left of these showers will be all rain.

Now for ALL the details with the Explanation of the Forecast and pictures below.

Remember, freezing rain is the worst type of winter weather because it’s rain that freezes on contact and accumulates. In these situations it’s all about 2 things: 1) where the rain/freezing rain line sets up, and 2) how many hours you’re in the freezing rain before it changes back to rain.

So what determines that line? Tomorrow we’re going to have low-level winds blowing cold air in from the northeast. I expect those winds to peak in the mid to late morning at around 15-20 mph. This will set up a shallow layer (1000 feet deep or so) of cold air. The subfreezing air will be closest to the source of the cold air, which is up north. So North Carolina will get all freezing rain – it’s going to be a mess. But the farther south you go, the warmer the temperatures in this shallow layer of air – hence all rain in places like Orangeburg. See pictures below.

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Where does the rain come from? A layer of warmer, moisture will flow up from the Gulf. This layer will ride over the top of the shallow cold layer. The rain that falls into the shallow layer will freeze by varying amounts, depending on how cold the air is through which it is falling. Again all freezing to the north (places like Rock Hill and Charlotte) and all rain to the south (places like Orangeburg and Aiken). See picture below.

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Below is my best estimate of where the rain/freezing rain line will be. Purple is freezing rain and green is just rain.

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And the Snow Showers? Yes we’ll get some of them early Saturday, but don’t expect much in the way of accumulation. As the low tracks up the east coast, we’ll get winds from the northwest. This will bring in cold air, which will be enough to sustain snow. But by that time we won’t have a lot of moisture left. Sorry snow-lovers wink emoticon See picture below.

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