Tuesday, January 20, 10AM

There’s a long way to go, but every model is in agreement that a significant storm will traverse the southern US and impact the mid-Atlantic region some time this weekend. Obviously, the exact track will determine the amount and type of precipitation we see, and over the next several days you might hear some newer terms that forecasters will use in explaining the possibilities. I’ll try to briefly explain those terms below so we all know what the heck they’re talking about.

Frequent readers know that I often refer to the GFS, NAM, and EURO weather models. The GFS and NAM are American models and, as you likely surmised, the EURO is a European model. There are others of course, including Canadian, German, and British models, but most forecasters rely on the American and European models. Recently, however, there have been AI additions to these models. I don’t completely understand how they work, but the traditional models are physics based and use complicated equations to make forecasts. The new AI models use historical data and pattern recognition to make their forecasts. Again, I may sound like I know what I’m talking about, but saying it doesn’t mean I understand it. Regardless, it is a new tool to use in forecasting, especially because they have shown some surprising accuracy, especially the aieuro inside 4 or 5 days. Additionally, the sometimes crazy nam is due for retirement in March of this year and is being replaced by the Rapid Refresh Forecasting System (RRFS), which is already available to the public.

So, as we track this storm over the next 5 days, I’ll refer to the traditional GFS and EURO, but also the AIGFS and AIEURO. As we get closer to the event (hopefully), I’ll also refer to the short range or mesoscale models like the NAM and the new RRFS.

With all that being said, where do we presently stand for the weekend? As I said in a recent WM post, there is an abundance of cold air available and over the next few days, temperatures will modify a bit until a strong surge of arctic air comes in later in the work week. Initially, most models showed the cold air keeping the weekend storm suppressed to the south, which is still a possibility, but recent trends have brought the storm more north so that every model now has central MD getting into at least some of the action. The GFS has been the most south, but the early morning run has become more in line with its AI brother and brings about 4-6″ of cold powder late Saturday and Sunday. The axis of heaviest precipitation in both models is along the VA and NC border. Looking at the European suite, both EURO models also have the axis of heaviest precipitation to the south, but both bring more overall precip to our area. The EURO and AIEURO are slightly different in how the storm plays out, but in the end, they both say anywhere from 8 – 12″ of snow in central MD. How this eventually plays out is impossible to predict, but the overall trend has been coming north so although suppression is still a possibility, it is becoming less likely.

Frankly, I like where we stand right now. At four or five days out, I much prefer the storm being to our south than on top or north of us. There are still a lot of uncertainties but hopefully we can reel this in and get a much needed region-wide snow event. Finally, and not to get ahead of ourselves, but the pattern looks to continue into the foreseeable future.

I’ll update as needed.