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If you have been digging out of those snow banks, you can blame the oceans. Scientists have been doing forensic work to learn what set this huge storm in motion. And as NPR's Christopher Joyce reports, they say they think the trail starts with the weather pattern called El Nino.
CHRISTOPHER JOYCE, BYLINE: El Nino starts in the tropical Pacific. Every few years, the ocean there gets unusually warm. This year is one of the biggest El Ninos ever. Heat and moisture from it have been swept up into the tropical jet stream and carried eastward. Climate scientist Michael Mann at Penn State says the warm, wet air was carried along like a wave in a rope.
MICHAEL MANN: If you flick it like El Nino is doing in the Pacific, you're going to generate this long wave disturbance that can have impacts way downstream.
JOYCE: The jet stream carried it to the southern tier of the U.S. Normally, that means wet and warm weather, but we got a blizzard instead. And here's why. Last December, just southwest of Alaska, a big, low-pressure system formed in the upper atmosphere. It was kind of like throwing a rock into the polar jet stream, another big stream of air blowing toward the East.
JEFF WEBER: So this kind of buckled the polar jets.
JOYCE: Jeff Weber is a climate scientist at the National Center for Atmospheric Research in Colorado. He says when that polar jet buckles...
WEBER: Instead of keeping all the cold air locked up to the north, it starts being able to bring that colder air farther down south, and that's exactly what happened for this storm.
JOYCE: To make matters worse, it also emits a very moist air from the Atlantic Ocean, which has been especially warm this year as well. When cold air met wet air, the result was the massive blizzard that swept the East. So El Nino apparently got this thing rolling. Will it do something like this again in future years? Climate scientists can't say for sure, but Penn State's Michael Mann says it depends on the oceans, and they are changing.
MANN: A lot of climate change is actually going into the oceans, and its changing the behavior of the oceans in a way that affects weather patterns around the globe.
JOYCE: And that's the leading edge of climate research now - finding out how a warming climate is changing global weather and El Nino's role in that. Now, if ocean waters are getting warmer - and they are - and El Nino is created by unusually warm waters, you might think we'd see more big El Ninos. Climate scientist Heidi Cullen at the research organization Climate Central says it's too soon to say that with any certainty. And, she says, even if they do get stronger, El Ninos are only one part of a very complex weather world.
HEIDI CULLEN: It's never just an El Nino signature that we experience when we experience any individual winter or any individual weather event.
JOYCE: Yes, scientists say a warming climate makes some things more likely - heat waves, droughts, big blizzards. But when it comes to your local weather, the deck is still full of wildcards. Christopher Joyce, NPR News.