Polar Vortex? It’s really just a blast from the past

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Record low temperatures have people around the nation talking about the “polar vortex,” but state climatologist Nolan Doesken says it’s really just a blast from the past.

“It’s surprising, we’ve been talking about the polar vortex in atmospheric science for decades, and now all of sudden everyone is blaming it” for the recent cold snaps, he said. “It does fluctuate in intensity and location a bit, but it’s just part of ongoing atmospheric circulation.”

But when cold air slams down into Colorado, Doesken prefers the term “Alaska Blaster,” which pretty much define winter cold snaps in which the temperature suddenly drops 40 degrees or more over a 24-hour period. Cold air pools deeper and deeper in Alaska and sooner or later it will spill down between the Rocky Mountain and the Great Lakes, inundating the western Great Plains with cold air.

While Colorado’s winter has been incredibly volatile, going from extreme cold to very mild in a matter of days; there has been some times when being blue in the face was an easy state to reach. For instance, the Alaska Blaster that hit in early December set a record cold temperature for Dec. 6 at Hohnholz Ranch in Northern Larimer County with a temperature of minus 41 degrees Fahrenheit, just one degree off the all-time low of minus 42 set on Feb. 2 of 2011.

This winter has been a return to the past with at least two Alaska Blasters — in early December and January — and an episode in late December that almost made the grade.

“The fact that we’ve had two, almost three, already this winter may seem unusual now, but it didn’t used to be unusual,” Doesken explained. “These last cold waves sort of caught some attention because they been colder (than more recent cold snaps), but they would have been no big deal back in the ’60s and ’70s.”

These occurrences were a lot more common until 1993, with four or five often occurring every winter. Since then they’ve been significantly less common, which is probably why someone had to dream up an atmospheric explanation like “polar vortex” that inevitably led to some interesting global warming discussions, as well.

And there have also been earlier times when northeastern Colorado didn’t see that many of the blasters, especially in the 1940s. Doesken noted that there were a number of commercial fruit orchards, especially cherry orchards, back then, before extremely cold temperatures wiped out a significant number of trees.

“Northern Colorado had a significant fruit industry, especially Buckhorn Valley, from Loveland to Masonville. There were little orchards all over the place,” Doesken said. “Basically it fell in line with a lot of agricultural entrepreneurship that was going on in those days — it was just a matter of whether you could get water to those trees.”

The legendary Alaska Blaster of 1951 may have felled a number of those trees. Taylor Park set a record of minus 60 degrees Fahrenheit on Feb 1, which was barely eclipsed by Maybell, far to the west, with minus 61 on the same date in 1985. Fort Collins hit minus 40 degrees on that same date in 1951.

Across the nation the thickness of the cold air has made for some very prolonged cold temperatures that have also managed to spill below the Great Lakes. In Colorado, the thickness of the cold air mass makes it cold across the state, with cold air spilling over the Continental Divide and into the western valleys.

The big question now, of course, is if these cold weather episodes are back for continued activity for this year and years to come. That’s really anyone’s guess, Doesken said, there’s really nothing special going on climate wise this year, for instance there is neither an El Nino nor a La Nina pattern set up in the western Pacific.

The Farmer’s Almanac did call for a colder than usual winter on the northern plains, but didn’t seem to hit on how far south the cold would go. For the record, it’s calling for continued cold in the northern plains during February with Colorado expected to see a slightly warmer than usual month.