When the snow falls early and sticks in Siberia, the polar vortex shudders, and the effects are felt across the northern hemisphere.
Or so says MIT’s Judah Cohen at Atmospheric and Environmental Research.
Cohen produces what might be the most interesting long-term forecasts you are likely to read in that they take into account not only the weather spinning around the planet, but the interactions between the weather at the grounded, human level and space.
“As I have written about previously in the blog, in producing a winter forecast the predictors that I most heavily rely on are the El Niño/Southern Oscillation (ENSO), October Siberian snow cover extent, November Arctic sea ice extent and high latitude blocking,” he reported on Monday. “To monitor how well the forecast is performing I will closely follow the vertical energy transfer from the troposphere to the stratosphere and the behavior of the polar vortex (PV).”
Cohen was hot on the PV as a major influence on the northern hemisphere long before it put middle America in the icebox last year and become a national talking point.
“Lake Michigan looks like a frozen tundra, with temperatures plummeting to 20 below as a polar vortex grips the Midwest, halting trains, closing schools and setting record-low temperatures.”
Much of Alaska, of course, tends to get the warm side of this climatological phenomenon. When the polar vortex – that swirl of air that forms above our spinning globe over the arctic – is disrupted, a ridge of high-pressure air regularly forms along the west coast of North America.
Weather moving west to east across the Pacific Ocean can’t bust through that ridge and ends up being pushed north toward Alaska. Can you say “Pineapple Express?”
It has become something of a regular visitor to Alaska since the dawn of the new Millenium.
“Typically by February, Alaskans are hoping for a reprieve from winter’s cold and snow. But this year, they’re experiencing a heat wave,” the Associated Press reported in 2003.
“Unseasonably warm weather has blanketed the state all week, marking a spike in a winter of above-average temperatures. Patches of brown grass poke through thinning snowdrifts and trees are bare of snow.
‘”We call it the Pineapple Express,” said John Stepetin, in the National Weather Service’s Anchorage office. ‘It’s a pretty big low-pressure system bringing up all the warm air from Hawaii and it’s going all the way up past Fairbanks.”’
Cohen links the Express to the polar vortex and the Arctic oscillation, though traditionally El Nino has tended to get most of the blame.
The good news for the winter of 2019//20 is that El Nino, a warm Pacific current that sometimes surges along the North American coast from near the equator to Alaska, is dormant this year.
The bad news is that Judah isn’t so sure that will translate into a cold, snowy winter for the 49th state – the kind of winter desired by snow machine riders, skiers, snowshoers, dog mushers, fat biker and many of the others who hang on in Alaska in the cold months rather than retreating to warmer climes.
“Arctic sea ice extent is well below normal and that is not going to change for the remainder of the fall and the winter,” he writes. “What is a question is where will the largest negative anomalies be focused on the North Atlantic or the North Pacific side of the Arctic?
“…Sea ice extent is below normal on the North Atlantic side but much more so on the North Pacific side. The predicted atmospheric circulation over the Arctic for the next two weeks seems favorable to me for sea ice growth on the North Pacific side of the Arctic so the situation remains fluid. I do (however) expect that negative Arctic sea extent anomalies to be favorable for high latitude blocking with downstream troughing and cold temperatures across the continents and probably for disrupting the PV, but the details remain unclear.”
Alaska would be the anti-continents in this scenario. The trough that forms to direct cold, Arctic air down into the heart of North America is defined by ridges east and west. The west ridges is the one that forces east-moving, warmth-packing, central Pacific storms north toward Alaska.
Predicting how this will all develop is part science and part art. Ridging is influenced by air pressure “anomalies” at sea level and Cohan says the most impressive of those “are in the Gulf of Alaska in the region of the very warm sea surface temperatures (SSTs) in the eastern North Pacific and it will be interesting to see if during the upcoming winter the warm SSTs and positive sea level pressure anomalies couple to form persistent ridging in the region.
“If the ridging remains offshore close to the Aleutians, this would favor cold temperatures over western North America like last winter. However, if the ridging is further east along the west coast of North America this would favor colder temperatures further east over the Central and Eastern US. I think though it is too early to predict one or neither of these scenarios.”
The latter scenario is the one that hots up Alaska. Well, not exactly hot but a lot warmer than normal with a tendency toward coastal windstorms and rain directed at Alaska’s urban core. Home to more than half the state’s population, the Anchorage Metropolitan area in the state’s underbelly seems almost perfectly positioned to capture this sort of weather.
The former scenario is the one that can bring Alaska lots of snow. It doesn’t take much of a temperature change here to make a big difference. A few degrees shift can mean the difference between rain and lots and lots of snow.
Which is coming this winter?
“I do think that Mother Nature likes to foreshadow the character of the upcoming weather season,” Cohen writes. “We are about to have our second very impressive snowstorm in the Northwestern U.S. and Southwestern Canada. That coupled with the summer-like ridge and hot temperatures in the Eastern U.S. is very reminiscent of last winter. So, is the weather of September and early October portending a repeat of winter 2018/19 for North America?
“I actually believe it is more likely a head fake than anything else, but I could be totally off on this early prediction. Across Eurasia if the snow cover advance continues at a pace more impressive than last fall, then I would read this as a sign of the likelihood of a harsher winter than last year.”
That prediction is perfectly in keeping with what old timers in Alaska will tell you about the weather.
It was always colder; it was always warmer. It was always wetter; it was always drier. There was always a lot of snow; there was never enough snow.
The climate records generally support that view in the sense that there are huge, year-to-year variations in a state where annual temperatures have been trending upward since 1925, according to the Environmental Protection Agency.
In the short term, which is easier to predict than the long term though not all that easy to predict, is forecasting a trough over the Western U.S. and Alaska that will pull cold air south and bring in some snow in the next six to 10 days with a West Coast ridge developing at 11 to 15 days out.
“This will favor normal to above normal temperatures across Alaska,” Cohen writes.