Get out the rain gear and the cleats for those walkways and roads that turn quickly from packed snow to slippery ice when things warm up.
The polar-vortex whisperer and Arctic oscillation monitor expects the latter will soon begin to weaken, spilling cold air into the middle of the continent and causing pressure ridges along the West Coast.
Alaska weather watchers know well what the latter means:
Warm, low-pressure weather systems tracking west to east across the Pacific Ocean get kicked north into the Alaska underbelly. Alaska temperatures climb. Snow starts to melt.
Skate skiing speeds up on the warmer snow until it gets so slushy the skiing slows down. Fat bike trails turn slushy and rutted. Holes open in creeks and rivers to mess with the snowmachine touring. Avalanches come down.
Winter as the state knew it earlier this month in all its white glory becomes a fond memory.
Temperatures around Prince William Sound and on the Anchorage Hillside were already touching 40 degrees by midday Wednesday.
Cohen on Monday predicted more of this to come.
“Over the next two weeks, ridging/positive geopotential height anomalies are predicted to become focused across Alaska, Northwest Canada and the Gulf of Alaska forcing troughing/negative geopotential height anomalies across eastern North America,” he wrote. “This pattern will increasingly favor relatively mild temperatures across western North America.”
This is something of the new Alaska norm. Four of the warmest years on record since 1900 have come in the last five years with 2016 leading the charge with a mean annual temperature for the year of 37.2 degrees.
Whether this Alaska warming is a short-term phenomenon or a lasting climate change only time will tell. As the Alaska Climate Center notes, the climate in the state varies considerably from decade to decade, and there is no clear linear trend as “might have been expected from the fairly steady observed increase of CO2 (carbon dioxide)” since 1949.
What is most obvious in a graph of temperature from then until now are the cold decades and the warm decades which have been associated with the Pacific Decadal Oscillation (PDO), which shifts water temperatures from cooler to warmer in the North Pacific Ocean.
The PDO has generally been in a positive, or warm phase, since the late 1980s which has brought Alaska warmer weather and bounties of salmon.
A well-published scientist, Cohen has linked sea-surface temperatures in the Pacific to Siberian snow cover and troposphere-stratosphere-troposphere (T-S-T) coupling events and come up with interesting ideas on how they affect the polar vortex – the swirl of winds that develop around the frigid blob of air above the ice at the North Pole as Earth spins its way through space.
Cohen is now a visiting scientist at MIT, one of the country’s great think tanks, and the director of seasonal forecasting at AER, a consultancy providing weather data to businesses sometimes making big gambles on weather.
All of which is to say that when Cohen talks about weather and climate he probably has a better idea of what he is talking about than your Facebook friends, and here is what he is now saying:
- Through the week, expect atmospheric ridging to “deepen and expand across Eastern Canada resulting in normal to below normal temperatures widespread across Canada with normal to above normal temperatures for Alaska.”
- Starting next week look for ridging “anomalies across Alaska and the Gulf of Alaska with…normal to above normal temperatures across much of Alaska.
- And as the month draws to a close figure on “geopotential height anomalies downstream over western North America centered over in the Gulf of Alaska with more troughing/negative geopotential height anomalies across eastern North America. This will favor normal to above normal temperatures across Alaska.”
The short version? Warm and warm and warm.
That prediction happens to be in agreement with the National Climate Center assessment from December which put the odds between 60 and 70 percent for Alaska temperatures coming in above normal from now through March.
The 2,000-mile Iron Dog snowmachine race from the Matanuska-Susitna Valley to Nome to Fairbanks in February has already abandoned its traditional Big Lake start because of concerns about warm weather.
The race will start this year at Deshka Landing near Willow, Iron Dog organizers announced this week.
“We’ve held off as long as we could on making the decision to move the start from its traditional home on Big Lake,” dog director John Woodbury said in a media release. “The Nov. 30 earthquake, combined with a slothy freeze-up and deep snow with overflow this year caused concern among our board of directors.”
A cold snap followed about a week later to put a solid layer of ice over the lake. There is now enough ice on the lake to support the traditional winter ice road, but the ice thickness is below the norm and the Iron Dog usually attracts dozens, if not hundreds, of motor vehicles on the ice for its start.
The good news for both Iron Doggers and the Iditarod Trail Sled Dog Race mushers who follow them north in March is that despite the warmth there is, at least at this time, a couple of feet of snow on the ground north into the Yentna River drainage, up into the Alaska Range, and across the north slope of the range in the Kuskokwim River drainage.
Big Lake is on the northern edge of the Anchorage Metropolitan Area, which saw a very warm end to 2018. October was 6.6 degrees above normal, and November even warmer at 7.9 degrees above the norm.
It has since warmed up. The National Weather Service ended 2018 predicting a low ice year for Cook Inlet at the front door of the state’s largest city, and the Wednesday forecast said “temperatures may be conducive for
melt rather than growth” this week.
At 1,000 feet on the Hillside above the Inlet, where the Wednesday temperature never dropped below 35 degrees and peaked at 41 degrees, the snow pack was settling fast.