With yet another immense North Pacific storm rolling into Alaska — complete with a closure of the Seward Highway southeast of Anchorage due to fresh avalanches, plus warnings of hurricane force winds and white-out blizzards by Tuesday night — let’s step back into the quiet before the screaming Chinook gusts and take stock of what winter has wrought so far.
Alaska just experienced its third warmest December on record, with temperatures averaging about 8.7 degrees Fahrenheit above normal, according to the latest analysis posted by the National Climate Data Center. At the same time, the state was splattered with the fifth “wettest” December – most of that precipitation piling up in big white drifts that blocked on-street parking and choked residential streets to single lanes.
Alaska’s weird warm-wet month was so unsettling, the climate agency listed it as one of the month’s most significant weather events in the nation.
December average 4 degrees warmer here
In a remarkable contrast, much of the western U.S. was bone dry. California, Nevada and Oregon saw the second driest December; Washington was third driest; Idaho fourth driest.
In Anchorage, where temperatures averaged 4 degrees F above normal to about 23 F, total precipitation was 71 percent above normal — most of that falling as 31 inches of snow, according to the preliminary climate report posted by the Anchorage forecast office of the National Weather Service.
Anchorage also saw more than 32 inches of snow in November. And yet that month was bitterly cold — the third coldest on record, with an average temperature of 14 degrees -- or more than 8 degrees F below normal, according to the monthly summary at the Alaska Climate Research Center. (Alaska as a whole saw the sixth coolest November on record, according to the National Climate Data Center.)
The result? As of Jan. 8, Anchorage had accumulated 38.9 inches more snow than normal for that date, according to the climate pages at this link. The city’s 81.9 inches is about 192 percent of an average winter’s early January yield. More snow may be coming soon.
So we get two successive months — one cold, one warm — both walloping southern Alaska with far above average snowfall and some of the strongest and most damaging winds on record. It has also smacked the Prince William Sound communities of Valdez and Cordova with building-crushing snow and tunneled streets — complete with a disaster declaration that brought in the Alaska National Guard to help with shoveling.
Alaska's weather as pulp thriller: Clash of the Oscillations
Big regional climatic patterns can work in synch to deliver wetter weather and more frequent storms to southern Alaska. But don’t look for a simple answer, especially when colossal North Pacific storms keep rolling ashore.
In general, high pressure over the poles combined with cooler sea surface temperatures in the Gulf of Alaska — combined with that infamous La Nina phenomenon that brings cooler waters to the coast of Peru — can work together to conjure a high-energy winter for the most northern state. That recipe can stir hurricane force winds in the Chugach Mountains and Turnagain Arm, blizzards in the passes, cold snaps on the backside of storms and those sloppy, drippy, ice-slick chinooks on the front side.
And sometimes, if everything lines up just so, if one of our North Pacific lows swings into position in the Gulf or PWS so that moist ocean air rushes over the land to marry frigid temperatures or bitterly cold flow down from the Interior, we get massive snow dumps.
Want more detail? The Arctic Oscillation is a polar weather pattern now considered to be in a positive phase. That means that high pressure is centered over poles with relatively low pressure at mid latitudes. Storms rolling out of the Bering Sea and along the Aleutian Chain tend to veer northward and deliver wetter weather to Alaska. Drier conditions prevail in the Western United States.
Sound clear so far? It gets more complicated. There’s another regional climate pattern having to do with the temperature of the sea surface in the North Pacific Ocean. The Pacific Decadal Oscillation is now in a negative phase, with water surface temps in the Gulf of Alaska cooler, which influences storm tracks.
And then there’s the La Nina — that infamous phenomenon where cooler water in the equatorial Pacific off Peru alters weather all over the globe. This year’s mild La Nina also has influence on Alaska’s weather, but scientists say it’s hard to gauge. It’s supposed to make Alaska both cooler and drier — a forecast still current at NOAA’s climate prediction center.
But if you add it all up — a positive AO, a negative PDO and the presence of a La Nina — Alaska can experience bigger anomalies, which creates a big potential for big snow storms and wet chinooks along Alaska’s southern coast, according to this research paper.
For more deep background as a way to understand this season's violent weather, check out the research papers posted by the local forecast office of the National Weather Service. Meteorologist John Papineau also discusses Alaska’s climate variability and the how La Nina and El Nino impact winter temperatures.