At 8 p.m. on Sunday, the temperature at 1,000 feet above Anchorage was an unseasonable 40 degrees and rain was falling steadily.

The normal White Christmas season was already long washed away. All that was left was the ice that clung to the ground anywhere snow had been compressed over the course of the past week.

Far below at Ted Stevens International Airport, the National Weather Service was reporting 41 degrees and forecasting temperatures to climb above freezing all through the week with snow, if there is snow, mixed with more rain. 

It was all very odd, but climate scientist Daniel Swain – a postdoctoral fellow in the Institute of the Environment and Sustainability at the University of California, Los Angeles – thinks he has an answer to what is going on.

He blames what he has labeled the “Ridiculously Resilient Ridge (The Triple R).” Swain first wrote about the latest rise of The Triple R  on Monday as the great Alaska warm-up was just beginning with rain moving first into coastal areas and then pushing over coastal mountains and inland.

Warm, wet, heavy snow was causing chaos in the Copper River Basin on the north side of the Chugach Mountains by mid-week, and by the week’s end it was raining in that normally chilly area.

Normal temperatures in Glennallen in the heart of the Basin range from a high of 8 degrees to a low of 10-degrees below zero in December. 

The temperature in Glennallen was above freezing most of the day on Sunday, but began to fall as nightfall set in. It is forecast to climb back into the low 40s on Monday. 

Credit, or blame, that resilient ridge of high-pressure air Swain says is anchored over North America’s West Coast.

“In the coming days, a remarkably persistent weather pattern will begin to develop across North America and adjacent ocean regions,” he wrote Monday on the California Weather Blog brought to you by Weather West. “Characterized by strong high pressure near the West Coast and low pressure over the Eastern Seaboard, this “quasi-stationary,” high-amplitude atmospheric wave pattern will essentially become locked in place for at least the next two weeks. Patterns like this have a tendency to become self-reinforcing, lasting for much longer than more typical transient weather patterns and leading to prolonged stretches of unusual weather.

“This particular event will be no exception: California (and much of the West Coast) will almost certainly experience an extended, multi-week warm and dry spell, while much of the East Coast shivers through repeated blasts of cold, Arctic air.”

Nailed it

From the looks of the country on Sunday, Swain couldn’t have come up with a prediction any better.

Hot, dry California was in flames, and the East Coast saw fluffies from normally snowy northern cities like Buffalo all the way south to Mississippi and Georgia. The Jacksonville airport reported almost 5 inches of snow.

For several years now, Swain wrote, he and his colleagues have been studying this particular “atmospheric phenomena.” The Triple R phenomena largely correlate with a string of warm Alaska winters caused by warm, low-pressure, weather systems spinning north out of the tropics instead of heading east.

All Swain missed in his Monday prediction was the way The Triple R would again block the normal eastward movement of weather systems and push them as far north as Seward’s Icebox.  But then nobody pays much attention the 49th state, except for its 700,000 residents and the millions of fans of unreal “reality TV” that provides a view of some fictional place even stranger than Alaska.

Alaskans have come to know the warm-weather phenomenon driving heat north as The Pineapple Express thanks to the Space Age. Weather satellites can now track weather systems as they move from near Hawaii across the Gulf of Alaska to smack into Alaska’s urban underbelly.

The Pineapple Express seems to have arrived with increasing regularity in recent years. Swain writes that he first noticed the Triple R appearing in 2013, and he and colleagues have documented it regularly since.

“Atmospheric pressure patterns similar to the Triple R are now occurring more frequently than they did in previous decades,” he writes, and “the unprecedented magnitude and persistence of recent West Coast ridging can be traced (at least in part) to regionally-accentuated warming of the lower atmosphere.”

As with much climate information, the new observations raise more questions than they answer, he adds.

“Climate model simulations,” he writes, indicate the Triple Rs appears to be tied to a generally warming climate, but it’s complicated.

“To date, the strongest evidence appears to implicate unusually warm ocean waters in the tropical western Pacific, which can trigger a hemisphere-scale wave pattern favoring an enhanced subtropical ridge near California. Other work has suggested that unusually warm ocean conditions in the “extratropical” Pacific (i.e. the so-called “Warm Blob” in the Gulf of Alaska) may also be linked to the persistent ridge—though there’s considerable evidence that the atmospheric Triple R caused the oceanic Blob, rather than the reverse,” he said. “Still others have wondered whether the striking loss of Arctic sea ice in recent years may have played a role, though the evidence supporting this connection remains sparse. Finally, it has also been shown that random variations in the atmosphere can occasionally produce an extremely persistent North Pacific ridge. In other words: the Triple R may be at least partially attributable to “bad luck.”

If you’re into weather, Swain’s blog is pretty interesting reading, and it ends with this thought to ponder:

“Interestingly,” he writes, “tropical Pacific Ocean temperatures during autumn 2017 were warm in the west and cool in the east amidst a modest (and ongoing) La Niña event—a combination that suggests a substantially elevated likelihood of West Coast ridging this winter. To date, Southern California has experienced one of its driest starts to the Water Year on record, and strikingly persistent West Coast ridging is now expected to last at least two weeks. It will certainly be interesting to see how this winter plays out in the context of these new research findings.”

La Niña was expected to bring a cooler water north along the Canadian coast and with that a more normal winter to South Coastal Alaska this year.