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Rain, cold and even snow possible this weekend

There, we used the “S word” in one of our posts for the first time this season. An energetic mid and upper level disturbance will shift from Central Canada through the Northeast United States late this week into the early part of this weekend, helping to develop a coastal storm. In addition to the coastal storm will come a strong cold front, and a cold Canadian airmass which will drop temperatures into the 30’s and 40’s at times after its passage. With models hinting at the development of multiple surface lows off the coast, the potential exists for not only rain and wind — but some snow in the higher elevations and the first flakes for others.

But the setup remains extremely complicated. The source region of the disturbance means forecast models are already working with a somewhat limited dataset. And, as is often the case with storms in our area, the mid level disturbances will be involved in fragile interactions, all of which will have a major impact on exactly how the storm develops. Confidence, as a result of these small nuances and features, remains very low.

What we do know for sure is that the energetic system will pass through our area late this week into the early part of the weekend. It will bring with it a noticeable cold front, with mid level temperatures falling below 0 degrees celcius. Even after any potential coastal storm, temperatures will be dramatically colder than they have been over the past few weeks, with low temperatures falling into the 30’s and possibly even 20’s in the interior.

The coastal storm’s development hinges on the aforementioned interacts aloft. A lead piece of energy will shift from the Tennessee Valley to the Mid Atlantic coast, helping to develop a weak low pressure system along the cold front which will have already moved east of our area by that time. But a secondary shortwave will dive southward from Central Canada toward the Mid-Atlantic states in the already cold airmass. This is the feature which we need to watch — for if it phases with the lead energy, a secondary coastal storm could develop a re-generate precipitation with an airmass cold enough to support snow.

GFS model showing lead energy and a coastal low off the coast, but a stronger secondary piece of energy dropping south from the Great Lakes.

GFS model showing lead energy and a coastal low off the coast, but a stronger secondary piece of energy dropping south from the Great Lakes.

Forecast models are up in arms regarding this potential. The general idea is that this phasing will happen too far east for any secondary coastal storm development to impact our area. And, quite honestly, this scenario makes the most sense given the pattern in the mid and upper levels. A strong ridge will be progressing eastward through the Central United States at the time that our coastal storm attempts to develop, as a result of another trough already crashing into the West Coast of the United States. Without any anomalous blocking to our north to slow down the pattern, this keeps the entire flow fairly progressive and doesn’t give our phase “time” to happen.

What needs to happen, then, is that the secondary shortwave needs to be energetic enough to dig southward, but perfectly timed with the lead disturbance to phase in an ideal location. If all of those pieces fall into the puzzle perfectly, a secondary coastal storm could develop and bring additional precipitation to our area. But, as you can imagine, the chances of this occurring are rather low.

What we, as forecasters, have to do over the next few days is analyze the trends on forecast models and continue to analyze and understand the pattern. If trends start to emerge for a more negatively tilted trough, and well timed phase, we can start talking about the potential for more than a few snowflakes in the higher elevations. But as it stands now, we’re leaning toward the idea that a coastal storm will develop — but too far east to bring significant precipitation to our area.

The cold front, meanwhile, still looks impressive. All models agree that a cold Canadian airmass, the coldest of the season so far, will race into the area behind the front and potential coastal storm. 850mb temperatures will fall to nearly -10 degrees Celcius, and overnight surface temperatures may fall into the 20’s across the interior. With blustery west winds, it’ll feel like early winter on both Sunday and Monday.

GFS model showing temperatures in the 20's on Monday morning and low 30's even near the coast.

GFS model showing temperatures in the 20’s on Monday morning and low 30’s even near the coast.

Stay tuned over the next few days for more information and updates on the very changeable pattern. Oh, and enjoy the near-70 degree temperatures today! We can almost guarantee you’ll be wishing for them to return by the time the 20 degree temperatures make an appearance in the early-morning hours on Monday.

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