La Niña has strengthened, what this means for N.J. this winter

Sea surface temperatures in the tropical Pacific continued to get cooler in October and November, setting up what weather experts are predicting will be a strong La Niña climate pattern during the upcoming winter.

So, why should something happening way out in the Pacific Ocean be of interest to us folks in the eastern United States, just a short car ride away from the Atlantic Ocean?

Turns out a La Niña pattern — just like its opposite twin, El Niño, when tropical Pacific waters get warmer — plays a role in weather patterns all across the globe. Many experts say what happens this winter could be influenced by the strong La Niña.

However, how big of a role it plays is a matter of debate, especially here in the New Jersey region. Although a strong La Niña typically generates colder, snowier winters in the far northern United States, and warmer, drier winters in the South, its impact on the northeastern and Mid-Atlantic regions — including New Jersey — is less certain.

“La Niña signals are not strong for New Jersey,” said State Climatologist David Robinson, whose office at Rutgers University maintains more than 125 years of weather data. “We are simply in a location where we are wedged between areas where signals are more consistent.”

During La Niña winters, Robinson noted, “the Ohio Valley and Great Lakes tend to be wetter than average and the Southeast drier. We’re in between, with most La Niña’s favoring precipitation close to average, not leaning toward an extreme in either direction.”

In terms of temperatures during the winter months, New Jersey rarely has big extremes — far warmer or far cooler weather — when La Niña conditions are present, Robinson said. Instead, the Garden State tends to have temperatures close to average or slightly warmer than average.

Based on past history, strong La Niña winters are more likely to bring less snow than normal to New Jersey.

The chart below backs up Robinson’s points. Of seven strong La Niña winters since the 1970s, most were warmer than normal, one (1998-1999) resulted in far milder than average temperatures across New Jersey and only one (2010-2011) had far higher snow totals than the state normally gets.

(Note: New Jersey normally averages 33.1 degrees during the winter season, 10.05 inches of overall precipitation and 26.1 inches of snow. Precipitation includes rain plus the liquid from melted snow and melted sleet.)

Recent La Niña winters

Jim Sullivan, a long-range forecaster for WeatherWorks, based in Warren County, agrees a strong La Niña generally results in milder winters for the New Jersey area, typically leading to average or below-average snowfall. But during some La Niña winters, the Garden State gets socked with heavy snow.

Sullivan analyzed all of the La Niña winters since the late 1980s — strong ones and weak ones — and found seven that were geographically similar to the current La Niña, with cooler water concentrated primarily in the eastern Pacific or over a wider area. (Some of the other La Niña winters had cooler waters mainly in the Central Pacific.)

He says these winters were most similar to the current cooling area in the tropical Pacific:

• 2017-2018
• 2010-2011
• 2008-2009
• 2007-2008
• 2005-2006
• 1995-1996
• 1988-1989

Of the most recent La Niña winters, the 2017-2018 season was colder than normal in New Jersey, where we had a string of small snowstorms in December, followed by a blizzard that lashed the Jersey Shore in early January and not much snow in February. Then March turned out to be a monster month, with an unprecedented cluster of four nor’easters that pounded our state.

With those coastal storms came a lot of snow, making it the snowiest March on record in North Jersey and one of the top 10 snowiest Marches in the rest of the Garden State.

During the 2017-2018 winter season, New Jersey ended up with an average of 40 inches of snow (the average among each region of the state), which was 14 inches higher than a typical winter but far from the statewide record of 62.8 inches.

Another fairly recent La Niña winter — the 2010-2011 season — was also a cold one with heavy snow totals. (The Newark area got 68 inches of snow that season, far above its norm of 28.5 inches, and the Atlantic City area got 38 inches, far higher than its seasonal norm of 16.5 inches.)

Not every eastern-based La Niña winter brings heavy snow to New Jersey. Sullivan notes the 2008-2009 winter turned out to be a near-average winter in terms of frozen precipitation.

The bottom line: Not all La Niña winters have the same impact.

Polar vortex also plays a role

Both Sullivan and Robinson stress La Niña is just one factor helping to shape our winter season. Another big one is the strength of the polar vortex — bands of frigid air circulating around the North Pole.

When the polar vortex is strong, it keeps most of its cold air locked up in the Arctic region, but when it is weak, it allows frigid air to drift down into the United States, boosting our chances of snow when storm systems develop.

La Niña winters tend to favor a strong polar vortex, so that usually limits snow in our region, Sullivan said. But even with La Niña conditions, that doesn’t mean cold Arctic air won’t drift down into our region every so often.

What should we expect this winter?

Based on the strengthening of La Niña and other atmospheric signals, Sullivan believes New Jersey will have some shots of snow in the first half of December (which is right around the corner). After that, temperatures will likely be up and down as we head towards Christmas, but colder air is expected in January, because there are projections the polar vortex may weaken at that time.

“Because of that, it could turn out that January is the coldest winter month for New Jersey, and the country in general,” Sullivan said. “January might be the best month if you want cold and some snow.”

Sullivan is anticipating a warmup in February, so he is not expecting much snow in New Jersey that month — which is usually the state’s snowiest month of the year.

Will March turn out to be a repeat of the brutal March of 2018, with all those nor’easters? Sullivan says it’s too early to make a call on that, but he will be closely monitoring the strength of La Niña, the polar vortex and other atmospheric patterns.

Robinson, the state climatologist, notes that “snow is awfully difficult to predict, as just one big storm can make the difference between a boom or bust seasonal total.”

“Still, coastal storms aren’t common in a La Niña winter, and the most common storm track through the eastern Great Lakes tends to transport mild air toward New Jersey,” he added. “Thus snowstorms, if they occur, may be white at the start and then turn to rain. Yes, not uncommon in many a winter, but more likely in a La Niña one.”

ALSO: How cold and snowy will it be this winter? Here’s what 6 forecasters are predicting

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Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com.