65 inches of snow buries Buffalo. Snow blankets half the Lower 48 a month before winter has even begun. All 50 states record freezing temperatures. The average temperature of the Lower 48 plunges to 19 degrees, the coldest in November since 1976.
Finding explanations for this recurring pattern has proven challenging. Like detectives, many meteorologists and climate researchers are investigating. They say it could be global warming, it could be the flow of winds 60,000 feet high, or maybe it’s just random chance.
Some background
Compared to average, for the past year, the eastern U.S. has boasted the coldest temperatures in the world.
Related: Eastern U.S.: Coldest spot on Earth so far in 2014 | The eastern United States: A lonely cold pocket on a feverish planet
Meanwhile, California is experiencing its hottest year on record, and drought covers almost the entire state.
Meteorological buzzwords that help describe the responsible patterns, the “ridiculously resilient ridge” in the West and “polar vortex” events in the East, keep appearing in headlines and news stories.
In this past week’s episode of a nation divided by weather extremes, the same features have played lead roles. A bulging jet stream, pumped up by the record-setting North Pacific storm or “Bering Sea Bomb”, sheltered the West but then buckled on its traverse to the East, giving the polar vortex an opening to drop south.
“When the polar vortex wobbles toward North America … it was like someone opened the atmospheric refrigerator on the North American side of the arctic,” said Lance Bosart, a professor of meteorology at the State University of New York-Albany. “The contents of the atmospheric refrigerator have been emptied into much of the U.S. east of the Rockies while northern Canada and adjacent regions have “enjoyed” anomalous warmth.”
Describing this pattern, as Bosart just did, is straight forward. No meteorologist can provide a bullet-proof explanation for why this pattern keeps showing up. But there a lot of plausible ideas floating out there.
Global warming
One of the more provocative theories is that global warming is driving what some have called this “drunk” weather pattern. Due to warming in the Arctic, the jet stream is becoming more wavy and prone to getting stuck, the theory goes, making weather patterns more extreme and persistent. Meteorology professor Jennifer Francis, who has written several research papers on the subject, said the pattern we’ve seen over the past year fits her theory “right on the money.”
“Last summer we saw the 6th lowest sea-ice minimum extent, and the extremely warm temperatures now over the Arctic are from all the extra heat absorbed by the Arctic Ocean where ice was lost,” Francis said. “When the Arctic is so warm, the west winds of the jet stream weaken, and this favors the highly wavy pattern to the jet stream responsible for this early winter chill in the eastern U.S as well as the continued drought and heat in California.”
But Francis’ theory, despite support from numerous scientists and independently published research, is controversial.
“I have heard lots of speculation about causality, but most of it is obviously wrong – like the global warming mechanism – or without real evaluation,” said Cliff Mass, an atmospheric science professor at the University of Washington. “This [the pattern we have now] has happened before (winter of 1976-77).”
A Pacific ocean cycle
Some meteorologists believe the weather is a simple reflection of a naturally varying pattern known as the Pacific Decadal Oscillation (PDO). For the last ten months, the PDO has been in its positive phase – meaning ocean temperatures off the West Coast of North America have been unusually warm, even record-setting. In this phase, a huge ridge in the jet stream over the western U.S. often results, which in turn directs cold air into the eastern U.S.
The stratosphere
Michael Ventrice, a meteorologist for WSI Corporation (part of The Weather Company), points to a pattern in the stratosphere as a key driver of the cold air outbreaks. Known as the Quasi-Biennial Oscillation (QBO), recent changes in this pattern help explain our frequent encounters with the polar vortex. Over the past year, the QBO has shifted into a state that favors the vortex’s break down. When it breaks down, large lobes of the vortex exit the polar regions, chilling the mid-latitudes.
“We have observed a sharp transition from what was a record setting QBO westerly state into a strong easterly state over the past year,” Ventrice said. “Recent research shows that when the QBO rapidly transitions into a easterly state, the mid-latitudes often respond by frequent high-latitude wave breaking events. These wave-breaking events act to force cold air down into the tropics and warm tropical air up into the higher latitudes.”
Explanations for the crazy weather pattern don’t end there.
Asian pollution
Strong storms that develop in east Asia can help enhance the ridging over western North America. A study on precipitation over China published in the Proceedings of the National Academy of Sciences found the particles from air pollution may be making storms out of this region more intense, and changing their tracks.
“Since the Pacific storm track is an important component in the global general circulation, the impacts of Asian pollution on the storm track tend to affect the weather patterns of other parts of the world during the wintertime, especially a downstream region [of the track] like North America,” Dr. Yuan Wang, the study’s lead author, told BBC.
And it’s not just manmade pollution potentially intensifying Pacific storms that set the U.S. up for extreme weather, but also acts of mother nature.
Asian volcanoes
Evelyn Browning Garris, a historical climatologist who writes a popular climate impact newsletter, has documented a flare-up in volcanic activity in Russia’s Kamchatka peninsula, likely adding juice to the Pacific storms that feed into the extreme U.S. weather pattern. She noted there was moderate-size volcano when the recent giant Bering Sea storm exploded, which precipitated the current cold snap.
“That area has been exceptionally active over the last few years,” Garriss said. “The volcanoes put a lot of aerosols or particles in the air which produce very thick clouds and microdroplets. When clouds precipitate out you get record-breaking snow like you see in Buffalo.”
Synthesis
So take your pick. The prevailing weather pattern may be related to global warming, naturally occurring decadal patterns, oscillations in the stratosphere, air pollution, volcanoes, or maybe some combination.
Yet John “Mike” Wallace, a professor of atmospheric science at the University of Washington, said perhaps the best explanation for the nutty, drunk, or crazy weather pattern is no explanation.
“I’m wary of statements about attribution,” Wallace said. “I think that most people (myself included) have trouble visualizing randomness. Whether it’s the unseasonable weather or an incredibly bad (or good) run of poker hands that seemingly goes on night after night, our memories tend to be selective, we have difficulty remembering past analogues to the current situation, and we’re continually amazed that random processes like the cut of the cards can give rise to what seems to be systematic behavior.”