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Don Paul: A follow-up on the Siberian snowfall connection

Much of what I’m presenting here is based on the work of researcher Dr. Judah Cohen, of MIT and AER, a private sector forecasting company. Some decades ago, he found a statistical correlation between above average October snowfall in Siberia and a tendency for a wintrier pattern across many parts of Eurasia and eastern North America.

In quite a number of autumns, Cohen fared better than most others in producing a winter outlook that factored in this correlation. This week, Cohen’s blog expresses higher confidence of a strong signal based on October snowfall, depicted on the Rutgers Global Snow Lab site.

[Related: Snowfall in Siberia may offer a hint of what's coming this winter]

Now that we’re past October, Cohen is projecting with higher confidence a colder than average winter across vast swaths of Eurasia with a near-term startup and, later in November, eastern North America. The abnormally heavy and rapidly advancing snow cover that occurred in October is the fourth most anomalous case he has studied going back to 1972.

The rapid advance of this year’s snow cover is another sign of the snow’s significance in projecting a winter outlook.

These anomalies, in concert with a weak polar vortex, will allow more frequent incursions of polar air into many parts of Eurasia and eastern North America. That’s right – a WEAK polar vortex. When the press caught on to the phrase “polar vortex” in the frigid winter of 2014-15, it was written about in a breathless fashion as a new discovery. In actuality, the polar vortex has been a known feature for many decades.

I think many reporters, viewers and readers assumed it must have been an extra-strong polar vortex that brought such a ferocious winter to the Midwest and the east. In fact, it’s the location of the vortex and its strength or lack thereof that matter the most.

A strong polar vortex located closer to the actual North Pole creates a strong west-to-east flow across the polar region, keeping polar air bottled up at high polar latitudes. However, if a strong polar vortex becomes displaced farther south, as was the case two winters ago, a bitter pattern can still develop over eastern North America.

In general, a weak polar vortex favors a flow across the polar region to more southern latitudes at more frequent intervals, instead of keeping it bottled up far north.

Researcher Cohen notes that the polar vortex is currently weak and that statistical probabilities favor its staying weak much of the time into the winter. The Siberian connection, he writes, will eventually favor a building mountainous ridge across western North America that forces the polar jet to cross the polar region and drop to the southeast into the Midwest, Great Lakes and much of the eastern United States.

If the polar vortex were to strengthen next month and during the winter, then all colder-than-average bets would be off if the vortex stayed closer to the North Pole. In any case, his hypotheses don’t preclude some ups as well as downs, and they don’t necessarily mean a very snowy winter for Western New York.

As I wrote last month, during a classic case of this connection's being borne out during the winter of 2009-10, Western New York was colder than average, but we had somewhat below average snowfall. The truly heavy snowfall was focused on the middle Atlantic states with powerful nor’easters sweeping up the east coast. The contrast between polar air masses and the air above the warm Gulf Stream can fuel the development of these vast coastal lows.

Back to the nearer term. There is good agreement in model ensembles of a sharply colder pattern developing across the Great Lakes around mid-November. However, the 46-day European model ensemble suggests this cold pattern will not be truly persistent and that there will be more ups and downs into the first part of December. Cohen’s own thinking favors a more persistent colder pattern not setting up in the eastern United States until near the end of November.

And in the truly near term, there will be absolutely no polar air anywhere near the lower 48 on Election Day, and there are no signs of major storms affecting the United States, either. As if weather would be a major turnout factor THIS year.

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