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Significant storm possible this weekend, details uncertain

Here we are again. Over the last day or so, forecast models have begun to come into agreement on a potentially significant Nor’Easter developing late this weekend into early next week. With a polar upper level low and associated shortwave energy dropping southward from Canada into the Great Lakes, a storm system will develop off the Northeast Coast of the United States on Sunday. But the devil, as always, is in the details. The exact positioning, orientation, and intensity of the mid level energy as it moves toward the coast will have significant impacts on where the coastal storm develops and how strong it is.

Not surprisingly, forecast models have been struggling to pin down the exact track and location of the aforementioned coastal low. Once it develops off the Northeast coast, there is good agreement on one thing: The storm will deepen rapidly. But the location where this occurs depends greatly on the track of the mid and upper level atmospheric energy. Some forecast models take this energy farther north, through New England, and develop the surface low too far north to affect our area. But others track it farther south, allowing the low to develop off the coast of New Jersey and bring snowfall to our area Sunday into Monday.

Not your typical Nor’Easter

Despite the fact that we’ve heard this general script before, it’s important to note that this isn’t your typical Nor’Easter shown on forecast models. First, the shortwave is dropping due south from the polar regions into the Northeast US. There is significant cold air associated with this storm, so barring any major changes precipitation type won’t be an issue in the forecast. Second, the storm system isn’t “phasing” with another piece of energy — it’s amplifying all on its own with the help of a major ridge on the west coast.

But third, and probably most notably — this storm isn’t coming “up” the East Coast at all. It’s actually tracking through the Great Lakes first, and then redeveloping off the coast of the Northeast States. This is commonly referred to as a “Miller B” storm, as opposed to a “Miller A” which forms to our south and amplifies up the East Coast. A Miller B storm, by definition, has a redeveloping surface low with an initial “clipper” low to its north and west. A Miller A is a primary low that moves up the East Coast.

A very basic depiction of what a Strong Miller B Nor'Easter looks like.

A very basic depiction of what a Strong Miller B Nor’Easter looks like.

Historically, Miller B events have favored New England. There are differences in every setup, obviously, but much of this has to do with the fact that naturally, New England extends farther to the east than our area. As a result, the Miller B redeveloping storm can mature into a well developed cyclone by the time it nears there area. January 22, 2005 is a prime example of a Miller B system (albeit a very different setup than this one).

A nod to New England once again

This setup, meteorologically, favors an axis of heavy snow over New England once again. When analyzing the mid and upper level atmospheric setup, it is clear that the disturbance entering the Northeast United States is quite amplified. However, there are a few other things to take away from the pattern. Most notably, the ridge on the west coast begins to lose amplitude as this storm is occurring. This means that instead of amplifying to the south and then forcing a surface low near the coast, the energy moves southeast through the Great Lakes and the surface low pressure develops from the NJ Coast east-northeast to a position south of Cape Cod.

Additionally, a lack of high latitude blocking exists once again with this event. High latitude blocking, a short way to define ridging or above normal height anomalies over Greenland or the Davis Straight for purposes of the NAO (North Atlantic Oscillation) is a mainstay in almost all analogs to major snowstorms in New York City. While we can get snowstorms without high latitude blocking, the presence of it acts to do several things: It slows down the mid level flow, it keeps cold air in place, and it allows for a more amplified pattern at multiple levels near our area.

GFS model showing a significant upper level low (top left) moving south into the Northeast. But notice how the worst impacts (bottom right) are shifted toward New England.

GFS model showing a significant upper level low (top left) moving south into the Northeast. But notice how the worst impacts (bottom right) are shifted toward New England.

With this in mind, it’s important to note that forecast models at this range, while indicating a storm, all show the worst of the impacts over New England. And, with all of this information ingested, this makes sense. The pattern over the past 3-4 weeks has been very wintry — but just progressive enough for our area to avoid crippling impacts from snowstorms — especially from New York City and west/south. Forecast models indicate, currently, that this will be the case once again.

Nevertheless, it’s important to note that this storm system is still 90 hours away. While the signal for a big event is increasing, forecast models are going to struggle with the details. The incoming polar upper level low is still in a very sparse data region. We expect shifts to continue on the models — and we will have to monitor which way they go. This storm system is by no means a guarantee to occur — nor is a a guarantee that New England gets another blizzard.

The most advantageous thing to do over the next day or so is stay tuned. We’ll have all the updates as we get new data and information — and we’ll forward them right along to you.

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