Clouds streamed across the plains from the mountains near Boulder, Colorado as temperatures plummeted and the winds kicked up on Nov. 10, 2014. (iPhone Photomosaic: © Tom Yulsman) I was blowing leaves out of my gutters this morning when the polar vortex arrived — suddenly and with a vengeance. It was 61 degrees and I was in a t-shirt when I clambered up a ladder to my roof. In anticipation of the snow that I knew was coming, I got the gutters cleaned out. Then, within five minutes, the temperature had dropped by what felt like 20 degrees, and the winds began whipping so strongly that I feared for my life as I gingerly stepped back down the ladder. I quickly jumped in my car to find a good spot to take some photographs. As I drove, stiff winds out of the north — I'd estimate the gusts at about 25 miles per hour — were blowing rivers of tumbleweeds across the road. Toward the south, sunny skies were becoming obscured by blowing dust as black, ominous clouds scudded across the plains. You can see these clouds in the iPhone photomosaic above, and in this photograph:
The high plains at foot of the Rockies near Boulder, Colorado on Nov. 10, 2014. (Photo: © Tom Yulsman) You've no doubt heard that frigid temperatures and snow have been forecast for a large swath of the U.S. midsection. In fact, it has already arrived over the Northern Plains — and, as I can attest — here along the Front Range of Colorado. And unless you've been maintaining a complete communications blackout, you've probably heard that it's due to the return of the polar vortex, a large cyclone of frigid air that's normally centered over the high Arctic. Why has a large chunk of it been displaced south? It turns out that the large Bering Sea superstorm that battered the Aleutian Islands kicked the jet stream into a large, northward bulge that brought a strong ridge of warmth-bringing high pressure over the Western United States during the weekend. Thus, my t-shirt this morning up on the roof... But the flip side of the bulge is a compensating dip in the jet stream that has allowed Arctic air to plunge south in a large trough of low atmospheric pressure.
A visualization of wind patterns at the height of the jet stream, as forecast by supercomputers. (Source: http://earth.nullschool.net/) You can see this pattern in the visualization above. The wavy feature separating the atmospheric ridge from the trough is the jet stream And now, as I'm about to publish this post, the temperature has plummeted to 27 degrees F and it is snowing like the dickens here in Niwot, Colorado...
