NEW YORK - With raging western wildfires to a record tropical cyclone season, 2020 has certainly been a year of weather-related extremes. Only the second time since the naming of tropical storms and hurricanes began in 1953, we went through the English alphabet and well into the Greek alphabet, too.
So you might be asking, "Could the large number of tropical systems this year have any effect on our upcoming winter?" The answer is yes and no. The number of storms isn't significant but the weather pattern that allowed so many to form will play a role in our winter.
You've likely heard of El Nino and La Nina, which reflect sea surface temperature oscillations along the Equator of the Pacific Ocean. El Ninos exist with above-average water temperatures strengthening the southern jet stream with La Ninas being the opposite giving more influence to the northern or polar jet stream. A La Nina has been around since May, which led to less intense high-level winds across the tropics resulting in more tropical cyclones.
Analysis of current Pacific Ocean sea-surface temperatures clearly shows a La Nina is still occurring and the forecast calls for this to continue to be the case into the spring.
In the past, you've also heard me speak of the PDO, or Pacifical Decadal Oscillation, which exists across the northern Pacific Ocean. Similar to El Nino/La Nina, it deals with sea-surface temperatures but phases can last more than 20 years. Like last year, the PDO is still the warm phase. The presence of these two events can result in a stronger northern jet stream.
Another important ingredient is the AO, or Arctic Oscillation, and what phase is present. A negative phase results in a weaker jet stream and a fractured polar vortex resulting in a colder and stormier pattern to much of the central and eastern United States. In a positive phase, polar circulation is stronger, which forces cold air and storms to stay to the north. Currently, the AO is positive and I believe it will stay that way most of the winter.
The Atlantic Ocean presents the NAO, or North Atlantic Oscillation, in which pressure differences are analyzed from north to south. The negative phase brings weaker low and high pressure in the eastern Atlantic setting up a block. Colder air is forced southward and we can get major snowstorms. The positive phase allows for a more northern jet stream resulting in warmer conditions and little in the way of snowfall. The NAO can only be predicted accurately a few weeks in advance, though I think it will be leaning more positive this winter.
I also like to check snow and ice cover across the Arctic to Siberia. It was a slow start this fall but snowfall has accelerated in recent weeks. More snow cover there can send more cold into the United States. Arctic Sea ice, though, is at a record low so I'm not sure how that will play into the equation.
What does this all mean for this winter? Mike Woods put it all together:
- A moderate La Nina remains in place
- PDO in the positive or warm phase
- AO averaging more in the positive phase
- NAO likely more positive than negative this winter
- Increasing Arctic snow cover but lower Arctic Sea ice
These all point to a more active northern jet stream and a more northern storm track, bringing numerous storms from southern Canada known as Alberta Clippers toward the Ohio Valley and then across New England. Thus, higher snowfall and colder temperatures can be expected from the Great Lakes/Ohio Valley region, across upstate New York, and into northern New England. The question will be how many of these try to redevelop along the East Coast.
For the tri-state area, the first part of winter may not be so bad with December through mid-January ending up a bit warmer than average. Cold outbreaks may only last a few days with longer periods possible in late January through mid-February, when we expect most of our winter cold and snow to occur. But in the end, our upcoming winter will be warmer than average.
Due to a more northern storm track, there will be more borderline snow to rain situations for New York City and along the coast and snow/ice/rain scenarios inland leading to a below-average snowfall forecast. The average snowfall for New York City is around 27 inches. I'm predicting 15 to 20 inches of snow for this season with lower amounts across central and southern New Jersey and eastern Long Island in the range of 10 to 15 inches. Areas to the north and west of the city should see a bit more snowfall, in the range of 20 to 40 inches.
With Mike Woods