Half-frozen Iditarod Trail Invitational hiker Tim Hewitt on the trail to the Alaska coldspot of  McGrath in 2014/Craig Medred photo

Coming off the warmest year in Alaska history, it’s been a rough month in the outpost community of McGrath on the north side of the Alaska Range.

The temperature there Thursday night was headed back toward 25 degrees below zero with the National Weather Service forecasting a further drop past 35  below by Friday night.

This or worse has been the story pretty much all month. The heatwave in mid-January wasn’t very hot and didn’t last very long. The temperature rose to a high of minus-8 before plummetting back to a night-time low of 28 below.

Still, the day was notable. It was the first one all month when the cold hadn’t been in the minus double-digits. The low came on Jan. 10 when the mercury fell to minus-45, but the rest of the days in the month weren’t all that much warmer.

Eight days in January dipped below minus-40, 19 were colder than minus-35, and 25 dropped to 30-degrees-below zero or colder.

At mid-month with the morning’s temperature at minus-35, Andrew Runkle, a tough guy who grew up in-country and has spent most of his life working outdoors, was moved to post a meme on his Facebook page observing that “it’s cold as hell and that rock tumbling around in your shoe is just your toe.”

By then, McGrath had been one of the coldest places in the state for a couple weeks. Not that it’s ever that warm in January in the community of 324 scattered along a handful of roads radiating out from an airstrip along the Kuskokwim River. 

Climate normal in McGrath in January is 2.3 degrees for the high and minus-15.3 for the low, according to the National Weather Service.  That’s cold unless you’ve spent a week with overnight temperatures dropping past 40-below and daytime temperatures never clawing above minus-30.

Then minus-15 feels positively warm.

Polar vortex

What is happening here is all about the winds spinnings around the sun-starved Arctic in winter. This is the polar vortex simplified.

Technically, it’s a little more complicated. The heart of the vortex is a pool of low-pressure air in the troposphere sitting atop a large mass of cold, dense Arctic air while interacting with the stratosphere.

When the vortex is strong, it rotates around the North Pole in a counter-clockwise direction and serves to hold all that cold, dense Arctic air in the Arctic.

Where exactly in the Arctic, or the near-Arctic, depends largely on where the vortex is centered. If it’s over toward Russia, Siberia gets the brunt of the cold. If it’s closer to Alaska, the 49th state freezes.

But the vortex isn’t always strong. It can shift and change and weaken, and, when that happens, it can influence weather far from the Arctic. For the last several years, it has been prone to weaken and fracture in a way that causes the jet stream to snake north across the Pacific Ocean and then south through the center of North American.

When it comes north, the stream pulls warm, moist air from the mid-Pacific into Alaska to warm the state, and when it later turns south, it carries cold, Arctic air down into the American Heartland to do the opposite.

So far this winter, the force in the PV has been strong, vortex guru Judah Cohen of MIT observed on his blog Monday. He is usually pretty good at anticipating what the PV will do next, but seems a little baffled by this winter’s developments.

“The models have been flip-flopping on whether the PV will become disrupted, but my expectations are for at least one or possibly two PV disruption of unknown magnitudes in February and March,” he wrote. “I don’t expect the PV to be as relatively strong in February and March as it was in January, but this forecast could very well be wrong.  I also don’t expect February and March to be as relatively warm across the Northern Hemisphere as January was but again that forecast could easily be wrong.”

Warmth as Judah uses the term there is relative. He’s describing a situation wherein the PV stays generally stays centered near the north pole and generally holds the cold Arctic air in that region. The rest of the U.S. states then avoid those “cold snaps” that come with PV air leaking south.

And the PV will eventually weaken; the cold air will slide south; and McGrath will eventually warm up, although it could stay locked in the deep freeze for a while yet.

As Cohen reads the shifting patterns of the currents in the atmosphere, they are most likely to “bring normal to above normal temperatures across Northeastern Canada, the Western and Northeastern U.S. with normal to below normal temperatures in Alaska, Northwestern Canada and the Southeastern U.S.” 

If there is a disruption that moves the cold elsewhere and allows some warm air to move into Alaska, Cohen doesn’t expect it until a week or two into February. Until then, the residents of McGrath will only be able to dream about the warmth of climate change while dealing with the vagaries of weather.

The scientific consensus is that the planet has warmed almost 2 degrees Fahrenheit since the late 1800s, and that the Arctic is thought to be warming more than twice as fast as the lower latitudes.

Bur even if the Arctic warms four degrees, the change is easily lost in the huge, daily variations in weather in the north. The historical temperature range for today in Alaska’s largest city, for instance, spans 61 degrees from a low of minus-17 in 1989 to a high of 44 in 1994, according to the National Weather Service.

A four-degree change to minus-13 would still be pretty cold in the warmer, gentler city most Anchorage residents have come to know over the course of the last several winters. A high near 50, on the other hand, might well generate headlines.