Monday, 11:10 A.M.
The weather turned balmy in the East over the weekend, and remains so today in advance of a strong cold front that is charging across the eastern Great Lakes, Ohio and Tennessee valleys to the central Gulf Coast. There will be some rain with the front in the next 24 hours or so as it moves steadily to the East Coast, and then offshore, but compared to Sandy two weeks ago, and the nor'easter of last week, it will be a very weak system. Unfortunately, another storm could be looming on the horizon for the week of Thanksgiving.
The ingredients for this to possibly happen are all there. A big high to the north over northern New England and southern Quebec. A developing split in the jet stream, with the southern branch likely to carry a couple of disturbances into the Southeast to cause low pressure to form. And with that split, slow movement of any storm that does form. About the only thing really lacking is cold air. Yes, it will be chilly behind this cold front across the South into the Southeast and up the Eastern Seaboard, and it will modify sufficiently during the second half of the week that it would seem very unlikely for there to be much snow, if any at all.
So, how can this happen? Again? It won't happen overnight, but there are several things that could allow it to happen. Following the cold frontal passage, a large high will migrate from Oklahoma this morning to the Ohio Valley tomorrow afternoon, then to southern Quebec Wednesday afternoon. That sets up an east to northeast flow up and down the East Coast, which, in turn, makes the Southeast more susceptible to low clouds and some light precipitation.
One weak, upper-level disturbance moving eastward across the northern Gulf Coast region will generate a fair amount of clouds later tomorrow into Wednesday, and there can be some light rain or showers along the Gulf and into the Southeast. Nothing major, just enough to help keep temperatures below normal.
In the grand scheme of things, this feature is nothing more than a bit player. It will ultimately merge with a feature coming out of the tropics Wednesday night and Thursday to deepen low pressure that may or may not get named, but will clearly be on the weather maps well away from the East Coast later this week. Here's the latest NAM surface forecast for Thursday morning:
Following all of this, high pressure reasserts itself over the Ohio Valley Thursday, a feature that will build east-northeastward going into the weekend. This will help to re-establish that east to northeast flow up and down the East Coast late this week going into the weekend.
Meanwhile, look at the jet stream flow late in the week. Here's the GFS ensemble forecast for Saturday morning:
Notice the split between the main branch of the stream that moves from the Northwest coast up into south-central Canada, then eastward to Labrador, and the southern branch beneath it? It's real, and there is likely to be another disturbance caught in this weak flow, one crossing the Mississippi Valley later Friday. As it continues to move slowly to the east-southeast Friday night and Saturday, it should help to lower the pressure over the Southeast coast over time. With the persistent east to northeast winds in place for more than a day ahead of all that, the lowering of the surface pressure should begin to transport more and more moisture inland - first over the Southeast, then spreading slowly northward along the Eastern Seaboard.
What happens after that is still a guess at this point, but the model trend today is clearly not a favorable one for areas from Cape Hatteras to eastern New England. Many models are showing the storm deepening Sunday and Monday, and just crawling up off the coast early next week. In fact, look at the Canadian model forecast for Wednesday EVENING:
That may be the extreme case of a storm forming, then an upper-level low forming over the Southeast and being left to drift northeastward over time heading toward Thanksgiving. But have we not seen those extremes already in the past couple of weeks? You can make a strong case it may be ready to happen again next week.
The worry is that you would have a lot of wind and rain over an area that just doesn't need any of it - and over a protracted time period. In other words, you see the gradient tighten this weekend, meaning the wind picks up along the coast. As the storm forms, deepens, and crawls northward, that surface pressure gradient then tightens, and you develop a long fetch of east winds that persists for two, three, possibly four days. I don't know what the numbers would be like, but the Navy NoGaps model from it's 6z Monday morning run at 180 hours shows this:
The lighter green shading is suggesting 7-foot seas, with the yellow 9, and orange 12. And that's with a much weaker low than virtually all of the other models at that time! If there really is a stronger storm, you'd have to think the waves would be higher. Bring that at the dilapidated East Coast beaches and coastal communities still struggling to recover from Sandy, and you have the makings of more widespread coastal flooding and destruction.
I really, really, really hope this does NOT come to pass. The mid-Atlantic into southern New England doesn't need anything like this. But my fear is this set up looks very realistic, and that the week of Thanksgiving we'll be talking about another battering of the beaches along the East Coast, rather than Thanksgiving travel headaches around the country.
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