The coming winter for the metropolitan area probably will be much like last year’s, slightly warmer than average, with the strongest snowstorms steering away from the region and going west toward central New York State, scientists said Wednesday.
The chief factor driving the National Oceanic and Atmospheric Administration's latest predictions is the La Nina weather pattern, which is sticking around, unusually, for the third year in a row.
“What typically happens, very often you’ll have less likely or enhanced chances of less snowfall in the mid-Atlantic and up into your region because of the storm track shifting further to the West,” said Jon Gottschalck, chief of the operational prediction branch at NOAA’s Climate Prediction Center, speaking of New York.
He told reporters on a conference call: “Warmer temperatures from the Atlantic can creep in … so typically, snowfall on average for the season is near to below normal,” explaining the winter forecast.
On Long Island, if this December through February stretch mirrors last year’s, the average high temperature will run around 43.4 degrees, the average minimum about 26.7, and the mean 35.1, according to the Upton-based National Weather Service’s records for Islip that began in 1963.
A total of 35.4 inches of snow fell during that period last year — but nearly two feet of that amount blitzed the Island in a memorable late January storm, recalled Jay Engle, an NWS meteorologist.
The exact total — 23.2 inches on Saturday, Jan. 29 — nearly set a single-day record at Long Island MacArthur Airport, according to the NWS. But the 24.7 inches that fell there over Friday and Saturday was well short of the 33 inches that buried parts of the Island over two days in the Blizzard of 2013.
Commenting on La Nina’s effects, Gottschalck observed, “Each event is different. … It doesn’t preclude having various snowstorms during that period,” referring to the coming winter.
The “triple dip” La Nina also continues the threat of destructive Western wildfires and drought hardship in farm country, the experts said. And it again could imperil shipping in the lower Mississippi River. Those are all areas where scant rainfall is anticipated.
La Nina, Spanish for "little girl," occurs when the surface temperature of the east-central equatorial Pacific Ocean cools. That can lead to warmer winters in the southern tier of the country, and chillier ones in the Northwest.
Its opposite weather pattern, El Nino, translated as "little boy," develops when those same waters are warmer than usual, bringing a milder winter to the northern and Western states and more rain to the Gulf Coast.
There are only two other recent periods that have seen three successive La Ninas: 1973-1976 and 1998-2001, said Tom DiLiberto, climate scientist at NOAA’s Climate Program Office.
Without more data, predicting how this third La Nina will behave becomes more uncertain. “It looks like it’s going to be another moderate event, similar to last year,” Gottschalck said.
Its opposite system, El Nino, “tends to be more reliable in some of the precipitation patterns across most of the country,” he added.
Further, La Nina is an outlier, as it is a long-term weather pattern. Said Gottschalck: “As far as storm frequency or intensity, we really can’t say anything reliably or concisely with respect to that at this early stage of winter; those are events that can be determined no more than a week in advance.”
Another uncertainty is how climate change might be weakening the polar vortex, swirling masses of frigid air around the North and South poles. Temperatures in this area can plunge if that air pushes down from the North. "At higher altitudes, it becomes a little more wobbly, if you will," Gottschalck said. "And when it's weaker, you tend to have more outbreaks."