Changing Arctic

No El Nino, But Sparse Sea Ice, Warm Ocean Water Portend Near-normal 2016-17 winter

KUAC | By Tim Ellis

Published October 21, 2016 at 1:02 PM AKDT

Arctic winter forecast: warm, with occasional normal weather ...

A year ago, National Weather Service meteorologist Rick Thoman and many other forecasters and climate researchers knew the winter of 2015-16 was going to be a warm one.

“We had warm sea-surface temperatures all around Alaska in the late fall,” Thoman said. “We had below-normal sea ice. And we had a strong El Nino.”

So, prognostications of the warm Arctic winter to come last year may be in hindsight as close to a no-brainer as it gets for the complex science of weather forecasting. And sure enough, the winter was the warmest on record, warmer than the previous record-setting winter and the unusually warm 2013 season.

A graphic of sea-surface temperatures, or SSTs, around Alaska shows some cooling over the past month in the Gulf of Alaska, but not so much in the Bering Sea. The scale at right shows the temperature-difference anomalies, compared with the norm, in Celsius.

“Last year was pretty easy,” he said. “The climate dice were all loaded toward warm for Alaska.”

But not so this year, Thoman says, largely because the warm-weather-inducing El Nino has faded away and been replaced by a quirky La Nina.

“This year,” he said, “I’m going to have to work for my forecast.”

Thoman says La Ninas generally portend a cooler winter for Alaska, south of the Brook Range, and more precipitation for areas along and near the coasts. But he says that tendency is going to be somewhat moderated this winter, because a couple of factors left over from last year.

“We have continued warm sea-surface temperatures near Alaska, both in the Gulf of Alaska and in the Bering Sea,” Thoman said. He added the seawater isn’t quite as warm as last fall, especially in the Gulf of Alaska. But as for the other factor …

Sea-ice extent is one of several factors that climate scientists consider when formulating forecasts. There's less sea ice around Alaska than there was a year ago, but Thoman predicts the winter of 2016-17 will be cooler overall than last winter, largely due to the influence of a La Nina phase that's replaced the El Nino that helped make last winter the warmest on record in the Arctic.

“We have even less sea ice near Alaska than we had last year, at this time.”

For those reasons, Thoman predicts the coming winter in the Arctic will be a bit warmer than normal – both here in Alaska and elsewhere around the region. But he concedes that forecast is mainly based on data from the past few decades, when the circumpolar north began to warm at an extraordinary rate.

“Because conditions now are so different than they were, say, in the 1950s and ’60s, we don’t include those older (data), and start, say, in the mid-70s” for a more relevant set of data.

Next week: The challenges of Arctic weather forecasting in a warming climate.

Editor's note: More information about climate change impact on Alaska is available through the Alaska Center for Climate Assessment and Policy.