Lars in the wind and rain on a Chugach Mountain trail turning to mush/Craig Medred

The cliffs above the Seward Highway along Turnagain Arm just east of Alaska’s largest city were coming apart on Saturday as December rains and wind swept into Southcoastal Alaska.

The Anchorage Police Department reported random rockfalls along five miles of highway in an area the Alaska Department of Transporation has warned was destabilized by a 7.0 earthquake that rocked Anchorage just a little over a year ago. 

Seasonally cold weather had helped to stabilize the area early in the month, but on the brink of the official start of winter, residents of the Anchorage Metro area were Saturday watching winter disappear as the hot air of a Pacific Ocean storm tracked north into the state’s underbelly.

After several winters with this pattern, more than a few Alaskans are starting to talk about a “new normal” that makes the weather in the state’s largest city look more and more like the traditional weather of the state’s capital city 575 miles to the south in the temperate, coastal rain forest of the Alexander Archipelago.

The changes are in line with global warming models that predict the capital city of Juneau will become more like Seattle while Anchorage became more like Juneau as climatic zones march north and bend along the Pacific coast.

Most people tend to think of those zones neatly stacked by latitudes south to north: Tropics, subtropics, temperature, subarctic and arctic. But it’s not that simple and would appear to be getting less so by the decade.

“The subarctic climate is found exclusively in the Northern Hemisphere between 50 and 70 degrees of latitude, in the interior of continents,” according to the website Sciencing. “Alaska, located above the northern Canadian border, has a subarctic climate. The Alaskan summers are short and cool, with temperatures averaging 17 C. The winters are very chilly, with short days. Alaska has very little precipitation, most of which comes in the winter in the form of snowfall. Summers are mostly dry with only occasional rain during thunderstorms.”

That description still applies to the state north of Alaska Range, but the demarkation south of the Range keeps moving upslope. Temperatures in Talkeetna – the Mount Denali jumping off point for climbers more than 200 miles inland from the Gulf of Alaska – were forecast to climb into the mid-30s today and hit 40 by Sunday as the latest storm pushed inland.

The National Weather Service was warning this is one of a “series of strong storms” pushing north.

Bad circulation (or good?)

Blame an imbalance in the polar vortex which causes a shift in high-altitude winds, and then get ready for a winter of this slop.

All climate models are suggesting a warm winter, but MIT’s Judah Cohen, an authority on the polar vortex, thinks they might be underestimating a coming polar disruption that could make the winter even warmer in Alaska.

“The American and European models all show widespread warmth across, Europe, Asia and the U.S.,” Cohen writes in his winter forecast for AER, a weather risk assessment company. “This winter’s forecast is consistent with other recent winter where the dynamical models have predicted nearly universal warmth across the Northern Hemisphere.

“I would attribute the (U.S. mainland) colder AER winter forecast to the anticipation in the model of a significant stratospheric polar vortex (PV) disruption with long-lasting impacts on the tropospheric circulation/weather.”

This is the disruption that heats up Alaska. The tropospheric winds bend to push warm weather systems out of the Pacific into Alaska then cool over the Arctic and curve back to the south to chill either the American Heartland or the East Coast.

“The region most likely influenced colder is Siberia followed by central and eastern North America,” Cohen writes. “The dynamical models either do not anticipate a significant PV disruption or that the disruption will not have a meaningful and/or short-lived impact on the weather.

“Therefore, a critical question for the winter weather and which forecast will favorably verify this winter – will there be an impactful PV disruption this winter?  The hemispheric pattern that set up in early to mid-November was highly favorable for disrupting the PV. With strong Ural/Scandinavian blocking and low heights near the Aleutians; and the PV has steadily but slowly weakened since the second week of November. ”

But Cohen admits the picture is complicated. Early Siberian snow cover, he said, argues for a major disruption; but normal amounts of sea ice in the Barents and Kara seas north of Russia – a change from the last two winters – argue against a disruption.

“Snow cover by itself might not be able to disrupt the PV sufficiently to force a major warming this year,” he writes. “Still based on the extensive snow cover, cold Siberia, generally low sea ice and warm Arctic, I expect more perturbations to the PV in the coming months followed by periods of more severe winter weather (for the Lower 48).

“Ironically though, low sea ice in the Barents-Kara Seas is favorable for disrupting the PV it does not seem to favor cold temperatures in the Eastern U.S.  Instead I believe that low sea ice in the Chukchi-Beaufort Seas and west of Greenland are more favorable for cold temperatures in the Eastern US.  Low sea ice in these regions support blocking near Alaska and Greenland respectively that often force troughing and cold temperatures in the Eastern U.S.”

Cohen believes the Arctic a big driver of weather, especially winter weather, in the Northern Hemisphere. If that is true, the lack of sea ice off Alaska’s western and northern coasts could have implications far beyond the 49th state.

“The anomalies in the North Pacific sector have emerged as the most well below normal,” Cohen observed. “Based on recent research low sea ice anomalies in the Chukchi and Bering seas favors cold temperatures in central and eastern North America while low sea ice in the Barents-Kara seas favor cold temperatures in Central and East Asia, however this topic remains controversial.”

What isn’t controversial is the west to east connection that usually sees temperatures warm in Alaska when they are cold in central and eastern North America. As this was written, a reported 13-degree temperature in Boston was 30 degrees colder than the 43 degrees at Ted Stevens International Airport.

The normal high for the date in Anchorage is 25 degrees, but it was 35 last year at the airport. Other locations in the city were warmer as they were also early this morning. The Weather Forecast Office reporting station in Potter Valley above Potter Marsh was reporting 46 degrees and the Upper DeArmoun road station reporting 44 with the winds building.

The winds were forecast to keep going up, way up. A high-wind warning calling for gusts to hurricane force was posted for Sunday night through Monday by the National Weather Service, which said southeast winds would rise to “45 to 65 mph with gusts to 90 mph possible.

“High winds could move loose debris, damage property, and cause power outages. Travel could be difficult, especially for high-profile vehicles.”

Welcome to the new Southcoastal Alaska winter.