When meteorologists put together their forecasts, they consider an array of variables: What systems are in the area? Will clouds bring in snow or rain? If so, will it be a sprinkling or a barrage of precipitation?
But some of the data used to come up with your local forecast comes from thousands of miles away, GBH meteorologist Dave Epstein said.
They’re called teleconnection patterns, “longer and bigger things in the atmosphere that help us to forecast more weekly and seasonal weather,” he said.
Teleconnections includeEl Niño, the Indian Ocean Dipole, North Atlantic Oscillation, the Arctic Oscillation and others.
For instance: This year is an El Niño year, meaning ocean temperatures in the Equatorial Pacific are unusually warm. That anomaly can shape the weather in New England.
“El Niño connects with kind of the global atmosphere and changes it over the course of each season,” he said.
Not every bit of weather we feel is necessarily a result of El Niño, he said. But different teleconnections, taken together on a global scale, can shape the weather we experience.
“All of these things, think of them like little switches, like light switches,” Epstein said. “Some of them put pressure for us to be colder, warmer, wetter, drier than average here in the northeast, but also all around the globe. And they're all interacting with each other.”
Think back to the winter of 2014-15. Boston got about 104 inches of snow that winter, with local weather patterns getting bolstered by global phenomena.
Say a nor’easter is approaching, Epstein said. He takes a look at different teleconnections: If the North Atlantic Oscillation is in its negative phase, as is the Arctic Oscillation, but the Pacific North American pattern is in a positive phase, his forecast may call for more snow that it would were all those factors reversed.
“That storm may, because it's coming in that pattern, kind of have a little more oomph to it,” he said. “It's kind of in the background, adding a little bit of pressure to make us a little snowier. Like in 2014-15, all those levers were pointed in a certain direction and we know what happened.”