For those who loathed or loved last winter's non-wintery Alaska weather, climate scientists have an important message: There is a good chance of a repeat this winter.
Forces at sea, in the atmosphere and on land, both short-term and long-term, are combining to create what might be a perfect storm of heat for Alaska. That means another much-warmer-than-normal winter is expected for Alaska and northwestern North America.
"You might not want to buy that 70-below parka," said Rick Thoman, the National Weather Service's Alaska climate science and services manager and one of the scientists focused on winter even in the warm days of Alaska's summer.
All of Alaska is likely to be warmer than normal in the next three months, according to the National Oceanic and Atmospheric Administration's Climate Prediction Center. Probabilities of unusual warmth edge up to 80 percent in the Gulf of Alaska coastal areas. The outlook extending into the next year also predicts warmer than normal temperatures for almost all of the state, with similar heat expected in the Pacific Northwest and the West Coast.
The warmth has multiple sources: persistently high sea surface temperatures, which are expected to linger; a shift into a positive and warm phase of the cyclical Pacific Decadal Oscillation; a powerful El Nino that is developing in the Pacific; and wavy jet-stream patterns that bring warm weather north and cold weather south.
"That's kind of in the background that everything's projected onto. Every year, that background gets a little brighter, a little redder," said Thoman, who prepared the Alaska section of the August/September/October forecast.
Such was the case with Alaska's extreme winter of 2014-15, with average surface temperatures running above normal by 4 to 10 degrees Fahrenheit from December to February and, in Anchorage, a record-low snowfall.
The weird winter was more the product of unusual short-term events than the gradual long-term warming resulting from human-caused climate change, said Nicholas Bond, a research meteorologist and climatologist at the University of Washington. Still, it was a sign of things to come, he said.
"This really isn't climate change, but it's kind of a precursor of it. This is what it's going to be more often in future decades," Bond said. "How many decades do we have to wait until this is the new normal? Is it the 2040s or the 2080s?"
And how much are the short-term warming factors exacerbating long-term warming? It is difficult to tell because systems are so complex, Bond said. But the combination may be creating some "points of no return," like thawing of permafrost that took millennia to form, he said.
'The Blob,' PDO, El Nino mean warm ocean water
Short-term forces that skewed Alaska's weather last winter are still in place.
Sea-surface temperatures in the Gulf of Alaska and the northeast Pacific have been well above normal since 2013, creating a mass of stationary warm water that is now called "The Blob," the term bestowed by Bond. The Blob is linked to abnormal winter weather, not just in Alaska and the Pacific Northwest but possibly across North America, and to disruptions in the marine system, including the large number of seal pup strandings in California.
Its origins are believed to be in the western tropics, though factors from elsewhere -- including the more rapidly warming Arctic -- might have helped create it or exacerbate it, Bond said.
Separate, but possibly related to the Blob, is the cyclical Pacific Decadal Oscillation, which started a positive phase last year, according to NOAA.
Negative phases, such as that which existed for about the past decade, are associated with colder temperatures in Alaska and neighboring parts of Russia; positive phases are associated with warmer temperatures.
El Ninos transfer heat from the western tropical Pacific eastward, usually bringing warm and dry conditions to Alaska and the Pacific Northwest and triggering a series of effects across North and South America. In 2005, one of the most recent El Nino years, global temperatures hit their highest level in a century, according to NASA, and Arctic sea ice shrank to what was, for that time, a record low in the satellite measurement era.
All El Ninos are unique, and the current one is associated with wider areas of warm water than even the record 1997 event, according to NOAA data. While warm sea surface temperatures usually follow the arrival of El Nino systems, the northeastern Pacific was already heated up prior to the start of this El Nino, a deviation from the normal pattern.
"We're a little bit in uncharted territory," Bond said.
Added to the other factors is the meandering jet stream that has been taking paths that loop north and south rather than its normal steady west-to-east movement.
The wandering jet stream is a short-term weather force and at the same time, according to an emerging theory, the product of long-term Arctic climate change. Rapid Arctic warming, outstripping the pace in the rest of the world, is venting heat and moisture into the northern atmosphere, upsetting the prior equilibrium that usually keeps Arctic conditions in the Arctic and southern conditions in the south, according to the theory.
Warming begets more warming
The most obvious sign of Arctic amplification -- the term used to describe the pronounced and self-reinforcing warming in the Arctic -- is shrinking sea ice, which creates open waters in late summer and autumn.
"As you lose that ice, then you're allowing a lot more evaporation. That extreme water vapor into the Arctic atmosphere has a huge impact," said Jennifer Francis, a Rutgers University climate scientist and meteorologist who has been studying potential links between Arctic warming and weather extremes in temperate latitudes.
More heat in the atmosphere holds more moisture, creating pressure ridges that then push the jet stream off its normal lateral course into a looping south-north pattern, according to the theory being explored by Francis and some of her colleagues.The result appears to be stuck weather patterns, and not just in the Arctic and Alaska.
Sea ice, when it is present, reflects solar energy, an effect called albedo. When ice is absent, dark ocean surfaces absorb heat. Changes in terrestrial snow cover also feed into the cycle, allowing solar radiation to be retained as heat instead of reflected on land too, Francis said. Clouds that form over warmer ocean and land areas trap heat in cold seasons, and the dynamic of cloud formation itself releases heat into the atmosphere, she said.
Effects of northern warming, like enhanced wildfires that emit smoke carried around the circumpolar north, and northward-advancing dark vegetation, stimulate more heat and melt, as was seen dramatically in 2012 in Greenland.
If Arctic amplification is skewing the jet stream, some potential results include the "Ridiculously Resilient Ridge," a phenomenon named and studied by Stanford University scientist Daniel Swain, that has kept California and the West Coast hot and dry; stagnant air that intensifies hazy air pollution in eastern China, a condition directly linked by Chinese scientists to reduced Arctic sea ice; extreme heat events in the mid-latitudes; and, most famously in U.S. East Coast population centers, the past few deep-freeze winter chills attributed to a persistent Polar Vortex.
One prominent sea ice expert, however, has yet to be convinced that Arctic warming is driving larger global weather patterns.
There is no question that the reduced sea ice affects weather regionally, as ocean heat that has built up over the summer gets released back to the atmosphere over places like Alaska's North Slope, Serreze said, pointing to dramatic temperature increases in autumn, the season on minimal ice.
There is also no question that the Earth is warming as a whole, and that this year -- thanks in part to El Nino -- will be another hot one, Serreze said.
"We'll almost certainly break a record high for global air temperature this year," he said. "That's almost a given."
But he has yet to be convinced that Arctic changes carry enough punch high enough into the troposphere to affect mid-latitude weather. It could be that the Arctic is more affected by the rest of the world, and "the sea ice is just kind of the tail of the dog" affected by warming elsewhere, not causing warming elsewhere, he said.
Researchers expect it will take many more years of study to determine conclusively whether Arctic warming is actually changing the jet stream and weather patterns far south of the region. For now, climatologists say, plenty of other factors are pointing to warmer-than-normal conditions in the months to come.
All is not doom and gloom for fans of snowy Alaska winters, however.
While temperatures may be warmer than normal, "That doesn't mean it's going to be another 20-inch snow year in Anchorage," Thoman said. "One storm could give you that."
And a positive Pacific Decadal Oscillation could quickly become negative, the scientists say.
"It can flip back, and it can do it quite abruptly," Francis said. El Ninos are generally followed by cold La Ninas, they say. Plus, uncertainties and day-to-day fluctuations can tip weather patterns, they say.
"All we can do is say the deck is stacked," Bond says. "The deal of the cards is going to be what the deal of the cards is."