'Arctic Oscilliation' Behind Season's Mixed Winter Weather
AUDIE CORNISH, HOST:
News cameras dutifully trained their eyes yesterday on the groundhog Punxsutawney Phil in Pennsylvania. He saw his shadow, meaning six more weeks of winter. But this year, for much of the country, that's great news. January was one of the least snowy on record, with more than 90 percent of the U.S. - some would say enjoying below-average snow cover. One theory for why? A phenomenon called arctic oscillation.
And here to explain how it works is meteorologist Jeffrey Masters, of the website Weather Underground. Welcome, Jeffrey.
DR. JEFFREY MASTERS: Hello, Audie.
CORNISH: So to start, can we get sort of a basic sense of what is arctic oscillation?
MASTERS: Before we describe what is the arctic oscillation, we need to understand the jet stream because the jet stream is that band of high-altitude winds that circles the entire globe, blowing from west to east. And it really influences our winter weather very strongly because the jet stream acts as the boundary between cold, polar air to the north and warmer, subtropical air to the south. So if that jet stream boundary is south of you, you're going to have very cold, wintry weather and potentially, heavy snow.
And if it's to the north of you - well, like it's been most of this winter over the U.S. - then you tend to have a very dry, snowless, warm winter. Now, the arctic oscillation is essentially a pressure pattern that drives the jet stream, and controls how strong its winds are and where the jet stream position is.
CORNISH: And when I was trying to look this up online, I saw one picture that was sort of a picture of the globe, with a kind of crown of wind circling at the top of it. Is that right, that sort of crown is moving up and down?
MASTERS: Exactly right. The jet stream makes a circle around the Northern Hemisphere, and that circle tends to have bulges in it. It doesn't flow straight west to east. Every now and then, you get a big dip in it, called a trough, and every now and then, you get a big ridge, which tends to push the jet stream far to the north. So these troughs and ridges are critical for determining our weather in the winter.
CORNISH: So does this explain, sort of, why parts of Alaska basically have been buried under snow and then you have Seattle having, you know, a pretty rare snowstorm?
MASTERS: That's right. We had one of these big bulges, called a trough, in the jet stream, that helped drive storms into Alaska and then Seattle. But over the rest of the U.S., we had one of these ridges where the jet stream went far to the north, and so we didn't have much snow.
CORNISH: Lots of folks have been talking about this crazy weather being, you know, climate change, essentially. And do you - is there any connection?
MASTERS: Well, at this point, we don't know. I have to say, I've been a meteorologist for 30 years, and when I look at the atmosphere over the last couple of years, it's really not the atmosphere I know anymore. There have been substantial changes. We've seen major perturbations to the rhythms I've grown accustomed to. And when you start seeing unprecedented events, like we've seen the past few years, you do have to look at, well, is there a major climate-altering force at work?
And, well, we know there are. There are a lot of heat-trapping gases, like carbon dioxide, going in the atmosphere. And those could, potentially, cause some of these unprecedented events, though we don't have any theory right now that can show exactly what's going on.
CORNISH: For those of us who don't want to rely on a groundhog to tell us how much winter there is left, is there anything we can learn - or you're seeing the trends with the arctic oscillation, that can tell us how much winter we really do have left?
MASTERS: Unfortunately, the arctic oscillation is not very predictable. It operates on a timescale of a week or two, and that's about all the advanced warning we have from our computer models as to what might happen. So I can tell you over the next week to maybe two weeks, things are going to stay about the same. Looks like almost no heavy snowstorms for the U.S.; continued above-normal temperatures. And we're on pace now to have our warmest winter on record.
MELISSA BLOCK, HOST:
Jeffrey Masters, he's a meteorologist with the website Weather Underground. Thank you so much for talking with us.
MASTERS: You're welcome, Audie.
NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR’s programming is the audio.