Despite a warm December sliding toward a balmy end along the Alaska Gulf Coast, the national Climate Prediction Center is sticking with its forecast that January, February and March are likely to return the 49th state to the long, cold dark for which it is famous.
Though this might make snow sport lovers in the north smile, the forecast also comes with a prediction for less than normal precipitation as well, and the three months in question are the snow shortest months – outside of summer – in the heavily populated part of Alaska.
The center’s Dec. 21 prediction does caution that its view of the future is based on statistical probabilities spun out of more than a half-dozen sometimes less than complimentary climate prediction models, and as such this is more a prediction of what might be rather than what will be.
So there is reason to hope the experts are wrong about the winter season, at least over the longer term.
Over the short-term, the forecasts tend to be pretty accurate, however. And January is looking to chill, according to the official experts, after a December on track to end 9 to 10 degrees above normal. The average was running 10 degrees high the day after Christmas, but the high temperatures that prevailed for most of the month have been trending down in recent days.
That said, December 2017 stands in stark contrast to December 2016 when Alaska ended its warmest year on a record with a final month three degrees colder than normal. About half of December ’16 was spent with lows in the single digits, and the temperature twice dipped below zero.
By way of comparison, the coldest day so far this year was Dec. 1 when the low temperature bottomed out at 11 degrees. The average high for the month, meanwhile, stands more than two degrees above freezing.
This will change, maybe
The climate center prediction for January on into the rest of the winter is heavily influenced by still-developing La Nina conditions in the equatorial ocean.
La Nina brings cold water from the deep ocean toward the surface where currents move it toward the coast of South America. The cold water in the gulf alters the movements of air in the atmosphere above.
“La Niña strengthened in November, and there is now a greater than 80 percent chance that it will continue through the winter,” according to the National Oceanic and Atmospheric Administration (NOAA). “The event is predicted to be a weak-to-moderate strength one.”
The latest NOAA tracking shows a broad band of cold water at the surface near the equator. In the traditional La Nina situation, the atmosphere responds by producing a high-pressure block of air that settles over the Gulf of Alaska and directs warm, eastward moving weather south of Alaska toward the Pacific Northwest.
The weather for the eastern part of Alaska seemed to be sticking to the model in November even though the state was unusually warm to the north and west. Anchorage was 1.3 degrees colder than normal that month. Yakutat was 1.5 degrees below normal. Juneau was 6.2 degrees below normal.
At NOAA’s climate blog, Emily Becker in mid-December observed that while one month “does not a season make…it’s interesting to note that this past month’s precipitation and temperature averages over North America resemble the expected La Niña winter pattern.”
Little boy winter
“For particularly strong La Niña years where the Pacific jet stream is retracted to the west, left in its wake are positive 500 millibar height anomalies…(that) are like adding a mountain onto the atmospheric landscape,” NOAA blogger Tim Di Liberto wrote. “This new obstacle causes any intrepid traveler – like a storm – to find another way around. All of which seems apropos given that this results in potentially more precipitation for the Pacific Northwest, or the end of the Oregon Trail.”
The mountain of high-pressure air to which Di Liberto refers is what keeps those famous “Pineapple Express” storms from down near Hawaii from swinging north and driving into Alaska’s underbelly. The storms instead follow a simple, west-to-east track across the Pacific into the Northwest, and colder air coming out of Siberia follows another simple, west-to-east track into Alaska and along the coast and across northwest Canada.
This is the pattern that appeared to be shaping up in November, and then that blocking high pressure that normally develops south of the Aleutian Islands moved east and set up along the North America coast.
There it formed what has been described as a “ridiculously resilient ridge” of high-pressure air over the West Coast of the Lower 48. Instead of a block kicking east-moving storms south, it sent them north.
The rain did end, and the temperatures did cool, but Daniel Swain, a NatureNet Postdoctoral Fellow in the Institute of the Environment and Sustainability at the University of California, Los Angeles, isn’t sure the “Triple R,” as he calls the ridge, is done messing with West Coast weather.
Swain is hot on the ridge, which is hot on California. When the ridge blocks east moving storms, it stops the winter rains that normally cool the state. California’s frightening problems with wildfire this year have been blamed in significant part on the ridge.
On Christmas Eve, Swain was pondering whether the ridge might return yet again, which put him somewhat at odds with the climate center.
“…Its return would rightfully raise some eyebrows, given recent research suggesting that such pressure patterns have indeed been occurring more frequently in recent years,” Swain blogged.
“My current answer: we’re not in Triple R territory quite yet, but we’re getting close. We have certainly witnessed the return of resilient ridging near California, but I don’t think we’ve yet reached the ‘ridiculous’ level of multi-month persistence that occurred during the height of the recent California drought. Should present conditions persist through January, and if seasonal precipitation has not started to recover from its early deficit by that time, I may have to revise that answer.”
Whatever the case, he added, “there has been – and remains – strong, multi-model agreement that West Coast ridging will persist for at least 1-2 more weeks.”
Forty degrees is roughly the latitude of the California-Oregon border. At the moment, that jet stream is picking up warm air from near the South China Sea and pretty much carrying it straight across the Pacific Ocean to near the U.S. coast where some ridging provides a gentle nudge to move some of that warm air north.
What the NWS in Anchorage describes as “upper level ridges over the Alcan border” block just enough of the flow to diffuse it into Alaska’s urban underbelly.
At some point, this pattern is sure to break. And a more northerly jet stream is expected to bring cold “polar” air into Alaska.
There are those scientists at the Lawrence Livermore National Laboratory theorizing that the loss of Arctic sea ice could be radically altering established weather circulation patterns in the North Pacific.
Their research raises questions as to whether the old rules apply.
Arctic sea ice has been rapidly growing since the end of November when the National Snow & Ice Data Center reported a “Record low extent in the Chukchi Sea,” but as of Christmas Day, there was still open water there and much of the Bering Sea remained ice free.
At Christmas, waves were lapping up on the beaches of St. Lawrence Island which is normally surrounded by ice this time of year.