Posts

John Homenuk

Arctic air arrives, multiple wintry chances late week

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Lets face it, the term “Polar Vortex” has become overused and oversaturated over the past few years. This time, however, it is certainly applicable: A piece of the polar vortex will be swinging southwards this week through New England, bringing with it extremely cold temperatures and an arctic airmass which is decidedly unusual for this time of year.

We spoke a few weeks ago about how the intrusion of this type of air was likely, due to the presence of a large ridge building from Alaska to the North Pole. The time has finally come, and the airmass over the Northeast US by the end of this week will feature temperatures 20 to 30 degrees below normal averages for this time of year.

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John Homenuk

Premium: Active pattern to begin December, but uncertainties remain

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The hemispheric pattern will continue to undergo changes as the month of December approaches, and this comes as no surprise to those who have been following our long range forecasts for the past few weeks. The main changes in the pattern are unfolding throughout the Pacific Ocean, where a large vortex in the Gulf of Alaska is being gradually replaced by a propensity for ridging. This causes a domino effect downstream towards the United States.

However, questions still remain in regards to the results of this change in terms of sensible weather. The source of cold air, speed of the pattern, and strength of individual storm systems are the main concerns; most stemming from the uncertainties in regards to the pattern in the higher latitudes from Canada towards the North Pole.

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Miguel Pierre

Premium: Late month pattern change likely to be gradual

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As discussed in the winter forecast, the stratospheric polar vortex has been weakened since late October. A wave-breaking event, mainly induced by a large ridge in the Kara Sea, has resulted in 100mb heat fluxes remaining above average. We still believe the polar vortex is likely to be weaker and more disturbed going into this winter, especially compared to the past several years.  However, some resistance from the polar vortex and tropical forcing influences will likely result in more gradual step down into pattern changes over next several weeks.

While westerly zonal winds have decreased to below average levels, a wind reversal or easterly winds aren’t being forecasted, particularly around 10mb and 60N. EPV at 10hpa also appears to shift from being poleward to more equatorward by the third week of November. Despite being severely disrupted; these winds allow for the polar vortex to remain quite large and profound over the high-latitudes. This will likely result in more neutral modality with the AO/NAO over next few weeks.

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John Homenuk

Seasons coldest air to infiltrate the Northeast this week

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The coldest air of Autumn 2016 to date will surge into the Northeast United States this week, as a deepening trough passes through the Great Lakes and Southeast Canada. After an initial surge of cold air earlier this weekend, secondary surges on the heels of multiple disturbances will arrive this week, and by midweek overnight low temperatures could reach 15 to 20 degrees below normal in some locations.

The airmass will settle in from Tuesday through Thursday before the approach of another storm system. Overnight lows on both nights will be very cold in the Northeast, especially in the interior. For agricultural interests, Freeze Watches have been issued as early as Tuesday Night– as a hard freeze may occur in some locations that have not experienced it yet this year.

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