Posts

John Homenuk

Multi-wave winter weather event possible next week

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A multi-wave winter weather event is increasingly likely to unfold during the early to middle part of next week across a large majority of the Northern 1/3 of the United States, initially in the Great Lakes and then northeastward into New England. The exact area where this winter weather potential sets up obviously remains highly uncertain. Forecast models have been extremely inconsistent in handling mid and upper level features which will eventually have major impacts on the sensible weather experienced by many. But in this case, there are clues in the meteorological pattern that point to the answers to some of our questions. Instead of looking specifically at forecast models and their trends, we can begin to look for answers to our questions in the hemispheric pattern. 

The winter weather threat traces its roots back to the total degradation of the West Coast ridge and positive PNA on along the West Coast of the United States into British Columbia. Inherently, this is a bad sign for snow lovers on the East Coast Any time we degrade a PNA ridge there is a positive mid and upper level height field response to the east of that over the Southeastern United States. In fact, the collapse of a PNA ridge can bring a response all the way into the Western Atlantic. As the amplified pattern out west collapses, the mid level jet collapses east into the Untied States and allows for the flow to enhance further to the east. So not only does the Southeast Ridge suddenly gain amplitude, but the pattern becomes more progressive over the Great Lakes and Southeast Canada — working against snow chances in the East. 

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John Homenuk

Monday’s snow threat trends north, still a concern

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The winter weather potential for late this weekend into early next week has been well advertised. A low pressure system is forecast to develop from the Ohio Valley into the Northeast states late this weekend, along a thermal gradient otherwise known as a baroclinic zone, and force the development of precipitation in the Northeast States. Forecast models, however, had been displaying tremendous uncertainty with the positioning of that thermal gradient — uncertainties which were well documented. The past 48 hours have seen forecast models trend farther north with the thermal gradient, changing the complexion of the storm threat completely.

What this means for our area, is that precipitation type and amounts become less certain. The thermal gradient, essentially, is a boundary where there is a large temperature gradient over a short distance. Along and just north of this zone, enhanced lift for precipitation can occur as the development of a low pressure system is promoted near or just south of it. With this gradient trending north, forecast models have introduced warmer temperatures in the mid levels, and have shifted precipitation northward into New England.

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John Homenuk

Significant coastal storm could affect the area this weekend

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If you hung your hat on a quiet and benign winter after the slow start to December and January, you may want to rethink things. Forecast models are in good agreement on a significant coastal storm — yes, a Nor’Easter — impacting the area this weekend. The storm is likely to form as a result of a significant mid level atmospheric disturbance, which will shift from the Four Corners region of the United States northeastward through the Mississippi Valley and eventually off the coast of the Mid Atlantic States.

The disturbance will force the development of a strong low pressure system, which will shift from the Carolina coast to a position off the Mid Atlantic States and eventually a position near the 40/70 Benchmark on Saturday evening. Forecast models, however, remain somewhat undecided as to the evolution of the energy in the mid levels of the atmosphere — and the evolution and strength of the surface low as it moves up the coast. Obviously, this will have a major impact on the conditions that our area experiences including precipitation type and intensity.

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John Homenuk

Significant winter weather event possible next week

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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.

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