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Don't count on a winter like last year's – but that's all Don Paul will say

I’d venture a guess that all of my colleagues around these parts have gotten social media requests for a winter outlook by now. Many such requests have been directed my way.

There is no shortage of winter outlooks to be found in social media, a few from bonafide meteorologists, but the majority from amateurs some of whose amateur status is quite rank (read: poorly informed). And I’ll leave the goofy Farmers’ Almanac forecast out of it altogether.

There are things I can tell you with some confidence. The odds of a repeat of last winter’s extraordinary warmth are quite slim. That doesn’t mean we’re heading toward the polar opposite – it means the key ingredient of last year’s warmth is no longer here.

Last fall and winter, we entered into the strongest El Niño since 1997-98. Strong El Niños are generally associated with warmer than average temperatures across most of the northern United States. Such a strong El Niño is a statistical gift for meteorologists formulating a winter outlook, because that warm correlation is a rare strong signal nature gives us of how winter temperatures are likely to go.

This year, like most years, we have a more subtle signal. El Niño is gone. El Niño is keyed to tropical Pacific sea surface temperatures’ greater warmth gathering farther east in the Pacific than average. That displaced warmth affects the upper air pattern and steering currents across North America and around the globe.

The placement of these warm waters is part of an irregular cycle called the El Niño Southern Oscillation, or ENSO. This year, most models which deal with ENSO are projecting a neutral ENSO; neither El Niño nor La Niña. There is good statistical evidence showing a neutral ENSO leaves the door open for other oscillating patterns to affect our winters. Buffalo National Weather Service meteorologist Robert Hamilton has found that a weak or neutral ENSO is associated more frequently with colder winters, and that there may be some correlation with increased snowfall as well.

If ENSO was the only variable, I’d be more comfortable venturing a first guess that this will be a colder, snowier winter, even this far out in time. Colder and snowier may well turn out to be the case. However, ENSO isn’t the only variable.

There are other oscillating patterns that cannot be predicted nearly as far in advance as ENSO. And there is one variable in particular which is different from all the rest.

A former MIT professor, Dr. Judah Cohen, has shown a relationship probably exists between how much snow falls over the vast interior of Siberia during the month of October and what the polar jet stream does over eastern North America and western Europe during the winter. His forecasts linking excessive October Siberian snowfall with a colder pattern over eastern North America have frequently gotten better results than winter outlooks issued by the NWS Climate Prediction Center forecasters, who are now beginning to take Cohen’s work into consideration.

I can’t take the space to flesh out the explanation in detail — after all, there are other articles here — but the main link is that the cold dome of air that builds over a snowier Siberian basin forces the polar jet to move up to where it can tap the coldest air over the arctic, while the famed polar vortex weakens. The jet then tends to dive down into eastern North America, dragging polar air with it. The contrast between this cold air and the warmer air out over the Gulf Stream can then spawn deep nor’easters along the east coast.

Anyone remember “snowmageddon” for Baltimore, Washington and Philly in the winter of 2009-10? That was the winter in which Baltimore received more snow than Buffalo, which was unprecedented in modern times. The east coast storms of that winter followed a very snowy October in Siberia.

Dr. Cohen had much better verification with his winter outlook in the autumn of 2009 than others did. However, this relationship is not airtight by any means. That’s because there are OTHER variables that can be predicted only about two weeks in advance that affect weather across our continent and around the world. Some of those variables can dilute, if not cancel out, the October Siberian snowfall element. In fact, last October brought above average snowfall to most of Siberia.

However, that was easily cancelled out by the exceptionally strong El Niño. This year, with a weak or neutral ENSO, odds increase at least somewhat to a return of a more typical winter around here because the strong El Niño variable isn’t happening.

It’s interesting to also note that more frequent excessive October Siberian snowfall appears to be related to a warming climate in the arctic. With arctic sea ice so greatly reduced, and sea ice minimums near record lows many years in recent decades at the end of the summer, there is increased evaporation from the Arctic Ocean. The additional water vapor can allow more snow to fall in Siberia in October than fell before warming in the arctic accelerated. Again, a warming climate can produce regional effects, which may be surprising to a casual observer.

But if I want to hang any part of my meteorological hat on October Siberian snowfall in formulating a winter outlook, obviously that’s a no-go in late September. This probably important variable will be an unknown for some weeks to come.

For now, I can leave you with a somewhat flimsier bottom line: the neutral ENSO doesn’t guarantee a very cold and snowy winter, but it makes a very mild winter unlikely. It opens the door for other variables to allow for a more typical winter over the Great Lakes. A more typical winter can still be somewhat milder or colder than average.

It’s simply too early to make a more confident outlook, other than “I’m confident we won’t be as warm as we were last winter.” In the meantime, I recommend using winter outlooks you run across this far in advance, even from reputable scientists, with caution.

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