With the polar vortex up to Halloween tricks, Alaska’s largest city is surfing toward November on a wave of weather historically more like early September than late October.
It has left some wondering about a climatological reorientation as Minnesota – the state that wants to rebrand itself “North” – shivered in the cold.
The midday temperature in International Falls on Tuesday was 27 degrees, which left that city on the southern edge of Canada’s border 26 degrees colder than the biggest U.S. city north of the Canadian border.
Temperatures in Minneapolis, Minnesota’s largest city, were forecast to dip to 22 degrees Tuesday night while the mercury was expected to stay above freezing in Alaska’s largest city with a forecast for temperatures in the mid-30s to lower 40s.
How unusual is this?
An Anchorage-area resident for most of his adult life, 63-year-old Doug O’Harra can’t remember a year in which Halloween wasn’t marked by either frozen ground or turf lost beneath a blanket of snow, though he concedes it is possible that might have happened sometimes in the past four decades.
“Memory is a leaky drybag with frayed seams,” O’harra admitted. National Weather Service records, however, aren’t.
The daily, climate “normal” temperature for Anchorage is usually at freezing by mid-October and falling fast. By Halloween, with daylight down to just a titch over eight and a half hours in length and the northern nights already long, the historic, normal, daytime high barely creeps above freezing to top out at 32.7 degrees while the nighttime low plunges to 21.3 degrees.
Not this year.
A record was set on Monday when the city’s high temperature hit 54 degrees – two degrees warmer than the previous record set in 2013 and 20 degrees above normal. The nighttime low of 42 degrees was 19 degrees above normal, according to the weather service.
Alaska climate trends over the last 42 years echo this weather report, according to the Alaska Climate Research Center, although the changes are not nearly as extreme except on the state’s North Slope where autumn temperatures in Utqiagvik (Barrow) are up a staggering 18 degrees.
Anchorage autumns have warmed by only 3.6 degrees, but that’s significantly above the average, annual, year-round warming of 2.1 degrees since 1976.
Swirls, swirls, swirls….
What is going on at the moment and has been happening with some regularity in the last several years is a ripple in the stream of air spinning around the globe.
Instead of northern hemisphere weather wirling neatly in a circle around the north pole, the polar vortex has been wobbling and kicking off pressure ridges in the atmosphere that can seriously mess up weather normal.
When a high-pressure ridge forms over the West Coast of North America, east-bound weather headed across the central Pacific Ocean is funneled north in the form of the aptly named “Pineapple Express,” “an atmospheric river…bringing warm and moist air all the way from Hawaii to Alaska” as the weather service describes it.
Meanwhile, behind the ridge to the east in the American Heartland, cold, Arctic air gets sucked down through central Canada into the Midwest in a pattern oddly reminiscent of the Wisconsin Glacial Episode an estimated 50,000 to 150,000 years ago.
The legendary “frozen tundra of Lambeau Field” in Green Bay, Wisc. was getting some of that frigid air this week. MIT climatologist Judah Cohen, the director of seasonal forecasting at Atmospheric and Environmental Research and an authority on the polar vortex suspects a winter-long pattern could be developing.
“…If you are a regular reader of the blog and/or my research then you are already familiar with my arguments that Arctic amplification, which not only includes amplified Arctic warming but low sea ice extent and high snow cover extent in the fall, is favorable for high pressure in the Arctic and downstream troughing and cold temperatures at least regionally across the northern hemisphere (NH) continents,” he wrote Monday.
Arctic sea ice is now at a record low, according to the National Snow and Ice Data Center, and October snow cover in the northern hemisphere is, in Cohen’s words, “relatively extensive.” He’s predicting this global-warming related phenomenon could, strangely enough, again put the big freeze on the Midwest.
“Based on my observational analysis,” Cohen wrote, the developing picture “favors high pressure in the Arctic with downstream troughing and cold temperatures across the continents. So, if you are considering Arctic predictors in your winter forecast, I would say that they are quite bullish for severe winter weather at least regionally (in the Heartland) and possibly on even larger scales if the stratospheric polar vortex gets involved.
“…In many ways this upcoming winter forecast is a good proxy or symbolic of the current debate whether accelerated Arctic warming is contributing to colder mid-latitude winters. The dynamical models clearly say no. I believe observational analysis says yes, and it will be interesting to see if this winter is consistent with the modeling or observational/empirical analysis.
Short term v long term
“Of course, one winter alone does not prove a theory or analysis but rather is one data point in a series or collection of data points,” Cohen added.
Only time will tell whether Cohen or the models are right, but the pattern is of interest to Alaska because the changes that bring winter cold to the Midwest bring the opposite to the 49th state.
At the moment, Cohen – like a lot of other climatologists – is watching “sea surface temperatures…well above normal around Alaska and the eastern North Pacific” which “favors, ridging over Alaska and the eastern North Pacific but I see mixed signals where the main axis of the ridging sets up. If it is along the West Coast like 2013/14 and 2014/15 the cold is focused in the central and eastern North America, but if it is offshore like 2017/18 then the cold is focused more in western and central North America.”
He also admits he is operating outside the scientific mainstream on this one.
“Of course, the dynamical models don’t agree with me and say ignore all that is going on in the extratropics,” he writes. “All that is important is that the Arctic is warm and if anything, that the warm anomalies will spread to the lower latitudes.”
In either of those scenarios, Alaska heats up, but in a land where just a few degrees shift in temperature can mean the difference between lots of rains and lots and lots of snow. Cohen is predicting normal or above normal pretty much through November.
He also sees possibilities for increased snowfall in Alaska. Whether that will come at all elevations is anyone’s guess. The problem is again a matter of a few degrees.
The weather service’s forecast for the week in Anchorage calls for temperatures above freezing with rain or showers almost every day. But at elevation to the south at Turnagain Pass on the Kenai Peninsula, the prediction is for near-freezing conditions with snow.
To the north where the early-season snow at Hatcher Pass in the Talkeetna Mountains has been a delight to skiers, on the other hand, the prediction is temperatures will warm up just enough to set the precipitation to flipflopping between rain and snow.
The good news for those who love winter sports is that coastal Alaska can get a lot of snow in temperatures at or even just above freezing. The bad news for those who love winter sports in coastal Alaska is that the weather now regularly goes Seattle like in any month.