In recent winters, the public has been introduced to concepts once relegated to deep meteorological geek-dom — like "polar vortex."
With long-range forecasters saying they are seeing some indications that the brisk storm traffic will continue for the next few months, this might be the winter that "Modoki El Niño" enters the popular lexicon.
Modoki — Japanese for "similar but different" — is a subphylum of the El Niño phenomenon, the periodic anomalous warming across thousands of miles of the tropical Pacific that affects winters in the United States in often-unpredictable ways. El Niño conditions are forecast to persist through the winter.
In the Modoki state, the warming is more pronounced in the central Pacific, to the west of where it is during conventional El Niño events.
"We don't use that term a whole lot," Stephen Baxter, a researcher and seasonal forecaster at the government's Climate Prediction Center, said of Modoki, "but they're not rare."
That said, "Our sample size is limited," he added, and thus insufficient to conclude much in the way of what they might mean to Philadelphia and the rest of the country.
However, he invoked two Modoki-influenced winters that would be enough to generate chills among the winter-phobes: 1976-77, the coldest in Philadelphia on record, and 2009-10, the snowiest.
In its updated winter outlook earlier this month, the Climate Center trimmed some of the warmth off its national map, leaving Philadelphia in the up-in-the-air zone for temperature.
The precipitation forecast does have coastal areas from the Gulf to southern New England in the wetter zones, which would suggest a brisk coastal storm traffic.
"Certainly I'd be surprised if there weren't a couple of major nor'easters," said Baxter.
The Commodity Weather Group's updated forecast issued Tuesday also shows the potential for frisky coastal-storm traffic. That's related to the Pacific warming, said forecaster David Streit.
It is impossible to say whether that would mean more snow than rain around here, he added. That would depend at least in part on the strength of El Niño. A stronger Pacific warming likely would mean stronger storms, but more rain. Weaker warming might mean weaker storms, but lower temperatures and more snow than rain.
In The Weather Company's winter outlook, released last week, longtime seasonal forecaster Todd Crawford opted for below-normal temperatures throughout the Northeast for December, January, and February — 2 to 3 degrees cooler than average.
That's a significant change from the three-month forecast issued in October, which had December warmer than normal, and January normal.
Crawford said the Modoki would favor a pattern of upper-air winds from the Pacific northwest delivering cold air to the east.
He said he also saw signs of a weakened polar vortex that would make it more likely to split off and drive Arctic air southward.
And he said that computer models from NASA and the Geophysical Fluid Dynamics Laboratory, operated out of Princeton, were lending further support.
The Climate Center's Baxter said that the well-regarded United Kingdom Met Office model is hinting at a general circulation pattern over the North Atlantic that would favor cold and stormy in the East, but "it's not an overwhelming signal," he said.
Conditions in the North Atlantic tend to be quite changeable and not predictable beyond a week or so.
And while conditions in the tropical Pacific tend to persist through the season, they hardly act alone, and El Niño-influenced winters in the Mid-Atlantic have been quite varied.
"So much else is driving climate variability over the United States," Baxter said.