NEW YORK (FOX5NY) - With November here, curiosity begins about what may be in store for the tri-state area in the upcoming winter season. Long range forecasting is by no means very accurate but we can look to a variety of features that are present around the world now or forecasted to take place in the near future to come up with an indication of what kind of winter we might experience.
One element that we begin to look at in October actually takes place on the other side of the globe in Siberia. A correlation can sometime be made but the amount of snow cover that has already established itself across Siberia. Below average snow cover there can lead to a milder winter for the east coast and a higher than average amount has resulted in a colder than average winter here. This year the snow cover is already well above average for this time of the year which may lead to a blocking pattern over the Arctic. Cold air being like molasses will have no place to go and thus drifts down across eastern Canada and the eastern US.
We then move our attention to the sea surface temperature along the equatorial latitudes of the Pacific Ocean. An above average ocean temperatures is known as an El Nino and a below average event is referred to as La Nina. Last year’s winter was dominated by a very strong El Nino which then tends to energize the subtropical jet stream. This brings more storms across the southern United States and if there is a blocking pattern over the Atlantic, those storms can then track up the east coast. We were fortunate last year that only one real major storm came out of that pattern which ended up producing the blizzard which set the record snowfall for one storm in NYC. More times than not, El Nino winters result in more snow for the tri-state area. But it is also related to the intensity of the El Nino during a particular year.
As this winter approaches it appears that we’ll be headed for a La Nina season but what may end up be a rather weak event. With a La Nina in play, the subtropical jet stream is weaker resulting in the polar jet stream becoming more dominant. While also talking about Pacific Ocean temperatures, we look to see what is happening in the North Pacific around the Gulf of Alaska. The Pacific Decadel Oscilation (PDO) deals with warm or cool surface waters in the Pacific Ocean, north of 20° North latitude. During a "warm", or "positive", phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. The positive phase leads to high pressure over the north Pacific allowing warmer air to be transported into Alaska and western Canada. This pulls the polar Jetstream further north across the western US and Canada but allows for that jet stream to dip south for the eastern half of the country, opening the door for arctic air to come streaming south.
Long range weather forecasts also take into account analog years where these factors were present and what was the resulting winter weather. La Nina years have not resulted in as many major snow storms as El Nino years but there have been some significant winters where lots of snow has fallen from a collection of smaller snow storms. Some of those years with a similar set up to what may take place this year are 1978-79, 1995-96, 2005-06, and 2013-14. Those years featured at least one major snow storm but also several small to medium storms. In fact the winter of 1995-96 brought with it 17 snow storms in total.
Other factors that are taken into consideration are the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). The AO is a climate pattern characterized by winds circulating counterclockwise around the Arctic at around 55°N latitude. When the AO is in its positive phase, a ring of strong winds circulating around the North Pole acts to confine colder air across polar regions. This belt of winds becomes weaker and more distorted in the negative phase of the AO, which allows an easier southward penetration of colder, arctic air and increased storminess into the mid-latitudes. So far this fall season the AO has been in a sharply negative phase.
The North Atlantic Oscillation (NAO) is a weather phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level from north to south.. It controls the strength and direction of westerly winds and storm tracks across the North Atlantic. It is part of the AO, and varies over time with no particular periodicity. The NAO also has both a positive and negative phase. In the positive phase, milder air is allowed to move up the east coast. In the negative phase, blocking over Greenland can result in colder air diving down from eastern Canada and a storm track up the east coast. Many of our big snow storms result from a negative NAO. Given its variability, the NAO can’t be forecasts accurately more than 2 – 3 weeks in advance.
As for the forecast for this winter, let’s look at what we know now…
1). Siberian snow cover well above average and northern Canada for that matter
2). Weak La Nina likely
3). Positive PDO
4). Negative AO
5). No guidance yet on NAO
From these factors, I’m thinking the winter of 2016-17 will end up being colder than average by about 2 to 3 degrees and will come in earlier this year. It should turn significantly colder for the second half of November and likely stay rather cold through February with spring coming a little earlier next year. Of course there will be some thaw periods but on average expect more cold days than mild days.
With regard to snowfall, my thought is that the storm track will be setting up just south of the area from the Ohio Valley to the east coast, leading to more complicated forecasts as storms will try to redevelop along the mid-Atlantic coast and then move northward. There will likely be 2 or possible 3 major storm threats but the La Nina influence may result in more of the small to medium size storms to dominate. So expect total snowfall for NYC in the 35-40 inch range versus the average of around 28 inches.
Keep in mind that lots can go wrong with these types of forecast. Just because we can correlate similarities to a previous winter, that doesn’t mean the same thing will happen this season. We can put forward our best ideas and hope that we’re on the right track. You know you can count on the Fox5 NY Weather Team to bring you the most accurate forecast and up to date winter weather information.
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