Concern rising for potential winter storm next week

The drum of what seems like an endless winter keeps beating on, and despite the warmth which has engulfed the area for a brief time this weekend, the beat will continue through the next 7 to 10 days. All forecast models agree on  below normal temperature departures becoming a common theme from the Central to Eastern United States beginning Sunday and continuing through the greater part of the upcoming week. Making things more interesting, undoubtedly, is the signal for a major coastal storm system on all forecast models and their ensembles. This has forecasters and hobbyists alike raising an eyebrow with eyes peeled on the potential system, which could impact the Eastern and Northeast US early next week.

Simply ripping and reading off forecast model’s specific outputs at this range, however, will get you nowhere. We’ve been down this road many times — several times this winter alone. A few operational forecast models start to show snowstorms in the medium range, a few people share it on social networks with big dramatic words, and suddenly all of the NYC Metro Area is lining up at Home Depot and Walmart. What needs to be understood is that, at this range in specific, any specific solution or outcome on forecast models is somewhat unlikely — and the bigger storm systems have very intricate details that won’t be ironed out until the event draws nearer. The counterpoint, with this system, however is the overwhelming majority of guidance now showing the threat. And when that starts to occur on operational and ensemble guidance, it becomes prudent to look at the meteorology behind the potential system.

GFS model showing a significant coastal storm staying east of the area early next week.

Originating in the Central Pacific, an upper level low pressure system is forecast by all guidance to shift eastward towards the Northeast Pacific ocean from the end of this week into this weekend. What in the world does this have to do with us,  you say? A whole lot. The upper level low over the Northeast Pacific drives a large and anomalous ridge up along the West Coast of the United States. This, in turn creates a very amplified pattern to the east over the Central United States. Any disturbance which were to dive south or southeastward on the east side of that ridge axis would have the potential to amplify fairly rapidly. And on most forecast guidance, the signal is for just exactly that to happen.

GFS model showing a ULL in the Pacific forcing a ridge on the West Coast.

The process, however, is far more complicated than it may seem. Forecast models, at this range, are indicative of two separate pieces of energy moving down the east side of the aforementioned ridge, and eventually ending up in the Central United States. The latter piece of energy is riding along the nose of a very impressive mid level jet streak, and eventually is forecast to race southeastward and phase with the initial disturbance. Should this occur, the potential would exist for a significant low pressure system to develop somewhere near the Eastern Seaboard. This is about where the confidence begins to decrease rapidly.

Working to support the potential for a major low pressure system is a broad, elongated lobe of the Polar Vortex over Southeast Canada and extending toward the Northwest Atlantic. Although not a classic 50/50 low by any means (what you want to see near the 50 long, 50 lat position in order to favor a major Nor’Easter), this feature will serve to slow down the pattern just enough and allow for amplification of a major trough — IF the forecast model guidance is correct in handling it.

GFS model showing two pieces of energy attempting to phase over the Central US.

As you may imagine, we are now beginning to reach the “mayhem point” as meteorologists like to define it, where forecast models are beginning to pick up on the potential. But all of the model guidance is handling the situation slightly differently, with individual perturbations, disturbances, and interactions in the mid and upper level flow having major implications on the eventual outcome of the system. And so despite knowing that the major players are more than likely to be on the field for a potential significant coastal storm, we don’t have any increased confidence in the track or intensity of the storm yet.

Should the two pieces of energy interact and phase as shown on some of the forecast models over the last day or so, a significant and powerful coastal storm system could develop — bringing widespread winter precipitation to a large area. That being said, even very slightly differences in the phasing interactions and timing could lead to a farther east or west track, or a weaker or stronger storm system.

As meteorologists, it is important to recognize the difference between potential and increasing certainty. And so we have attempted to do exactly that: Recognize the potential as we described above, but make clear the fact that considerable uncertainty still exists in regard to exactly how the next several days will play out.