Ask Dave Epstein: What do teleconnections tell us about the local forecast?

february_2014_north_american_winter_storm_13_feb_1745z.jpg — A large winter storm, classified by some as a bomb cyclone, tracked across the East Coast in February 2014, producing heavy snowfall.

Dave Epstein is a meterologist who partners with GBH News to provide daily weather updates and weekly higher-level conversations on Morning Edition.

Gal Tziperman Lotan is a digital producer for GBH’s Morning Edition.

December 05, 2023

Paris Alston: You're listening to GBH's Morning Edition. All right, folks, get ready. We could see the first snow of the season tonight with some flurries in the forecast and even a coating in some areas.

Jeremy Siegel: But predicting exactly what we'll see in the forecast, from when and how much snow will get to how cold this winter will be to how warm the next summer will be, is tough to do. Here to explain the science behind one of the key tools that experts use to predict changes in weather and climate around the globe is our meteorologist Dave Epstein. Good morning, Dave.

Dave Epstein: Good morning. Good to be here.

Siegel: So before we get into this science, I just wanted to ask: What exactly are we expecting tonight in the forecast? Anything actually bad that would be like, school closures, snow plow needed? Or just a light dusting?

Epstein: Absolutely not. Yeah, just a light dusting, and some places might not see a flake. So it's kind of scattered snow showers. Think of it like in the summer when I might be forecasting scattered showers and thunderstorms. Someone gets a downpour, somebody gets absolutely nothing. I think that the downpour in this case would be a coating to half an inch, maybe an inch on the grassy surfaces. It should be over probably between about 9 and 11 tomorrow morning. And so a few spots tomorrow, you'll be seeing some pictures of snow. But again, it's not, it's not a big deal.

Alston: Okay. So as Jeremy alluded to there, Dave, you use something called teleconnections to predict that. Now, not to be confused with telecommunications, which is what you're doing right now, but this is a way of figuring out predictions. Tell us more about this. What are teleconnections?

Epstein: Yeah, So teleconnections are longer and bigger kind of things in the atmosphere that help us to forecast more weekly and seasonal weather. So I'm not really looking at — for the snow showers tomorrow, we're not looking at, hey, how is El Niño going to affect snow showers tomorrow? The snow showers tomorrow are too small. They're just basically noise in the El Niño. But El Niño connects with kind of the global atmosphere and changes it over the course of each season. So we have these various teleconnections. El Niño is probably one of the more well-known ones, but there's also the Indian Ocean dipole. So this is where parts of the Indian Ocean are going from warm to cool in two different areas. That's the dipole, two Poles. There's that one. There's the North Atlantic Oscillation, there's the Arctic Oscillation, there's the Pacific North American pattern. And all of these things, think of them like little switches, like light switches. And 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. So another way to think about this is: Each of these things has their own kind of thing that they're going to do. And when they get together, they can also start interacting and playing off each other. So much like a sports team you put together, you know, you've got your quarterback, you've got your cornerback, you've got the rushers and all that. But sometimes when they all get together, they play off each other in ways that maybe aren't predictable, and it's the same thing. So El Niño, we're in a warm phase of an El Niño right now, but if all the sudden Arctic oscillation kicks in and gets really strong, this winter becomes really negative, That might overwhelm what we thought was going to happen because of El Niño. Conversely, if El Niño gets really strong, that might overwhelm the North Atlantic oscillation and what we think is going to happen with that. So it's pretty complicated stuff.

Siegel: We're talking with GBH meteorologist Dave Epstein about a prediction tool that meteorologists use called teleconnections. So, Dave, when someone tunes into GBH and hears you saying what the week is going to look like or what the season might look like or pulls open their phone to check on like, how's it going to be Saturday and Sunday? Am I going to have a good weekend? The forecast that they see, or the trends that they're seeing, is essentially determined by something that's literally happening on the other side of the world?

Epstein: Yeah, it can be. It's sort of like, it's fuel for what we see happening. So, for example, if we have a nor'easter coming up, right, there's a nor'easter coming up, let's make it January. And we know that the North Atlantic Oscillation is in its negative phase and the Arctic oscillation is in its negative phase, and the Pacific North American pattern is in its positive phase — all those things point to colder and snowier. So that storm may, because it's coming in that pattern, be a little more, kind of have a little more oomph to it than it would if all those things were opposite from what I just said. That's how it kind of works. 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.

Alston: Oh, my God. Almost like a little butterfly effect here in so many ways.

Epstein: A little bit, yeah.

Alston: This would be a really great science fair project for somebody's kid, I must say. This is fascinating. Well, that is meteorologist Dave Epstein. Dave, thank you so much, as always.

Epstein: You're welcome.

Siegel: You're listening to GBH's Morning Edition.

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.”