Significant winter weather event possible next week

Forecast models have come into much better agreement regarding a storm system which is forecast to impact the area early next week. Several days ago we mentioned in a blog post that the next significant precipitation event wouldn’t come until early this coming week — and that idea continues. A powerhouse upper level trough will slam into the West Coast over the next day or two, providing much needed rains. But more interestingly for us, the associated energy will de-amplify somewhat, but eject northeastward towards the Tennessee and Mississippi Valleys. As a result, a surface low pressure system will develop from the Arkaltex towards the Mid Atlantic coast.

To our north, a piece of the Polar Vortex will be meandering in Southeast Canada, maintaining an impressive low level cold air source. The result of the ejecting shortwave and cold air to the north will be an impressive thermal gradient and stalled frontal boundary, which will extend from the Central US towards the Mid Atlantic. Along this thermal gradient, a plume of moisture is forecast to develop in response to enhanced lift from the aforementioned disturbance. Accordingly, areas to the north of this thermal gradient (including much of our forecast area) will be in line for a potentially significant winter weather event.

GFS model showing a large-scale winter weather event impacting the Eastern United States early next week.

GFS model showing a large-scale winter weather event impacting the Eastern United States early next week.

The details of the potential event remain somewhat uncertain at this time, but there are a few major things to note as we approach the weekend. The atmospheric setup features several different moving parts, all of which will have a major impact on the eventual sensible weather outcome of the storm system.

Pacific Energy: First and foremost, comes the Pacific energy which will eventually be the focal point for the development of a surface low over the Tennessee and Mississippi Valleys. This energy comes ashore on the West Coast, moves through the Southwestern US states, and then ejects northeastward; eventually to a point off the Mid Atlantic coast early next week. Forecast models differ slightly (as is to be expected at this range) in regards to the amplitude, strength and positioning of this feature.

Most notably, the amplitude of the disturbance as it moves through the Mississippi Valley will determine the degree of warm air advection which occurs ahead of the system, as well as the amount of lift which develops for heavy precipitation. In essence, a weaker and more progressive disturbance would mean a more progressive and colder outcome. A more amplified, consolidated disturbance could lead to an event with more moisture and precipitation, as well as the possibility of warm air in southern and central parts of the area leading to precipitation-type problems.

GFS model showing two major features in the development of the storm system -- the pacific energy to our southwest, and piece of the polar vortex to our north.

GFS model showing two major features in the development of the storm system — the pacific energy to our southwest, and piece of the polar vortex to our north.

Polar Vortex/etc: A close second in terms of importance, a piece of the Polar Vortex will be settling into Southeast Canada during the time that the aforementioned disturbance moves through the Central United States. This is a critical part of the setup, as it helps to keep low level cold air locked in to the north of the area. When the low pressure system develops towards the Mid Atlantic coast, northeasterly winds around its circulation will then be dragging in fresh arctic air; owing to the piece of the polar vortex being well positioned to our north.

The exact placement of this trough over Southeast Canada will become imperative in forecasting the track of the low pressure area as well as determining precipitation types. Most forecast models have the trough positioned so that a sprawling high pressure system will develop, at the surface, to the north of the developing low pressure system to our south. This would serve to keep low and mid level cold air locked in place while moisture overspreads the area. As you can imagine, any small fluctuations in this feature’s positioning will have major impacts.

Thermal gradient: A thermal gradient (or boundary between warmer and colder temperatures) is forecast to develop throughout the Central and Eastern United States as the storm system develops early next week. The gradient will develop as a result of the amplification occurring ahead of the shortwave/disturbance, and the piece of the Polar Vortex pressing southward to its north. This thermal gradient will serve as a “highway” for the track of the mid level centers (at 700,850 and 925mb).

Typically, the heaviest precipitation develops just to the north of these thermal gradients, as mixed and winter precipitation. But along and south of the gradient, a sharp cutoff in winter weather is sometimes observed. Forecast models currently indicate this gradient will be mostly south of our area, but a more amplified solution could lead to some precipitation-type issues in Southern New Jersey. The exact positioning of the gradient will help forecasters determine where the heaviest precipitation/winter accumulation will occur.

GFS model showing a noticeable thermal gradient (temperature boundary) at 925mb.

GFS model showing a noticeable thermal gradient (temperature boundary) at 925mb.

Bottom line: The potential is higher than normal for a winter weather event, with impacts potentially beginning as early as late Sunday night into early Monday morning, and continuing into Tuesday. The atmospheric setup features several different moving parts, but forecasters currently have about “normal” confidence for this range — which is a rarity for winter storms at this range so far this season. Most have been much lower confidence. The event could feature several hazards including:

Snow: The potential for moderate to significant snowfall in a fairly widespread area. The potential for this is currently higher than normal, but confidence is still too low for us to begin talking about amounts or snowfall accumulations.

Ice: Forecast models indicate the potential for freezing rain and sleet near the thermal gradient and developing low pressure system as a result of mid level warming. Where this thermal gradient sets up currently remains uncertain, so confidence is low. That being said, areas south of Trenton currently have a higher chance of experiencing mixed precipitation types as opposed to areas north of Trenton.

Travel: The storm system, as currently modeled, would impact rush hour travel on Monday (AM and PM) and Tuesday (AM). Although the system is still a few days away, and confidence is not high enough to call for major travel impacts, we suggest that you keep the storm in mind. If you have secondary travel arrangements that you use during hazardous weather, begin to consider them.

Potential changes: Keep in mind that, although confidence is average for this time frame, changes in forecast models can and do often occur. The exact track of the system will ultimately determine how much winter precipitation falls, where it falls, and where precipitation-type issues occur. With this in mind, note the potential as we have described above, but remember that no specific solution is currently favored and the situation as far as forecasting is concerned remains a fluid one.

Over the next day or two, our forecasters will continue to analyze new data and information. Confidence should continue to gradually rise as we approach the event, and we anticipate more information regarding timing and snowfall amounts becoming available within 24-48 hours.



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