A week ago, a winter storm brought record low temperatures to the Western states. Cold outbreaks aren’t uncommon there in early December, but the severity of the chill amazed forecasters and the general population alike.
Great Falls, Mont., reported minus-33 degrees, which hadn’t been seen this time of the year since 1972. In Casper, Wyo., the mercury dropped to 22 below zero.
Invasions of Arctic air this early indicate the greater variability that we’ve been seeing in the weather patterns recently. When ocean temperatures are higher than normal, the warm air pushes toward the poles and makes a tall bend, called a “ridge,” in the flow pattern of the upper atmosphere. It looks like a tall curve in a roadway.
At the same time, the opposite bend, termed “trough,” develops over the North American continent. This allows for a pool of very cold air from the Arctic to push deep into the northwest and west of Canada and the U.S.
Traveling in its usual direction, from west to east, the fast airflow at high altitude is forced to go through a counterclockwise turn. It’s equivalent to a long sweeping left-hand curve on the highway. Counterclockwise turns of the atmosphere enhance the formation of low-pressure cells, which always spin in that direction in our hemisphere. This explains the long periods of rain we had during the days before last weekend.
If the cooling of far-north regions continues at the same pace, we may get a “Siberian Express” situation again this winter. An air mass over the northern half of the Eurasian continent can get so cold and heavy that it overruns the North Pole, crosses into Canada from the top of the world, and deals a hard wintery blow to the southeastern states.
Thirty years ago, Gainesville experienced this when the thermometer hovered around freezing on Dec. 22, and 1.15 inches of rain quickly turned into an ice storm the following day, followed by another half-inch. Roadways turned into skating rinks and the official low for Hall County on Christmas Day 1983 was 1 degree below zero. It took us until Dec. 28 to make it above freezing again.
The taste of winter that the West got last week is a good reminder to consider adding to the insulation of the house, check the antifreeze level in the car and make sure the battery is in good working condition.
Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.