Last year on Dec. 8, two weeks before the official start of winter, who can forget the nationally televised South Philly snow blitz of an NFL game between the Eagles and Detroit Lions?
Shady McCoy entered the annals of Philly sports lore juking his way through what seemed at times like mountains of snow.
More snow fell in an eight-hour period (8.6 inches) that day than the entire prior winter of 2012-13, and more than double the amount from two winters ago.
It was indeed a harbinger of the winter ahead, as Philly endured the second snowiest winter of all time — a whopping 68 inches, falling shy only of the all-time record of 78.7 inches in the winter of 2009-10.
The winter of 2013-14 was relentless, with a historic four snowstorms of more than 8 inches of snow each. That has never happened in the history of keeping records for the last 130 years here in Philadelphia. Keep in mind that snowstorms of more than 5 inches in a day happen on average only once a year in Philly from December through March.
With all that said about last winter's breathtaking relentlessness, here's my analysis of the upcoming winter of 2014-15.
It would be unprecedented, and quite frankly astonishing, if we were to pile up another 68 inches of snow this winter. This should not happen. But you can never use the word "definitely" — not in the meteorological world. In all my 30 years of forecasting, there is always a surprise waiting to happen.
(Despite the many hours each year looking at the models, my motto with long-range winter forecasts has always been that they are like ticking time bombs. They can blow up at anytime as the atmosphere shifts into an unexpected mode.)
As hard as I tried looking for signals of a gentle winter, especially coming off last year's wicked one, almost all of the signals point to another harsh winter ahead. Here's an in-depth breakdown for how I came to this conclusion.
Winter forecast: 2014-15
A look at the atmospheric players in developing a long-range winter outlook:
ENSO: This winter, we should stay in a weak-to-moderate El Nino. This phase would normally keep temperatures slightly above normal. A weak-to-moderate El Nino also should add some fuel to the fire as far as providing some additional moist energy into coastal storm formation.
AO: This weather player is very significant when it comes to how much snow and cold weather we get. When the AO is in a positive phase, winds in the upper atmosphere tend to blow strongly west to east across North America, keeping Arctic invasions to a minimum in the east. When it's in the negative mode, the Siberian arctic high strengthens, leading to more frequent Arctic dips into the east. Also, the polar vortex tends to extend southward, leading to some very harsh winter setups and well-above-average snow amounts. Right now, I'm favoring an overall negative positioning due to the extent of Siberian snow cover.
Siberian snow cover: The more I read about Siberian snow cover, the more I'm convinced this COULD be the most significant weather player in predicting winters here in the east. MIT's Judah Cohen is a strong proponent of using Siberian snow cover as a winter forecasting tool and he said Siberian snow cover got off to its fastest start since he started tracking the index in 2000. When I compare last year's snow coverage across Siberia with this year, my alarm bells go off. Snow coverage is greatly ahead of last year, which should lead to a colder-than-normal winter and an extension of the polar vortex southward. That would lead to a possible strong negative phase of AO, starting sometime in mid- to late December and continuing into mid-February. This translates into a cold and snowy time frame.
PNA: The waters across the Pacific Northwest and the Gulf of Alaska are running above normal. This means the Pacific/North American teleconnection, at least for now, is in a positive mode. This is not positive for us. When PNA is positive, high pressure ridging takes place across the Pacific Northwest and the mountain regions of the upper Midwest. The high pressure ridging will allow for periodic trough formation in the East, meaning the probability of storm formation along the East Coast increases along with the possibility of more frequent arctic outbreaks. The future tracks of these storms and what impact it has on us will be up to the ultimate wild card: the North Atlantic Oscillation.
NAO: This is really tough to forecast. But know this: When the NAO is in the positive mode, that equals less snow. When it's negative, that equals more snow. Unfortunately, this wild card has only about a three-week forecast window. But what I have learned in the past is when the waters are warming around Greenland — they currently are running above normal temperatures — high pressure ridging is more likely to form, causing a blocking pattern and not allowing storms to escape out to sea south and east of us. This is a tough call, as a negative NAO favors above average snow chances.
So, in summary:
By agonizing over this winter forecast for weeks, it appears that we are in for another rough winter, with periods of Arctic outbreaks and well-above-normal snow amounts.
The onslaught of winter should start to hit in mid- to late December and continue with harsh frequency through mid-February. We will have occasional breaks in the pattern as the atmosphere at times will go through a reloading phase.