The impact of record-setting cold accompanied by heavy snow cover was at least Topic 1-A during the winter and early spring producer conferences and trade shows. It’s quite likely that no one who experienced the harsh 2018-19 winter will ever forget it.
This past winter had the term “polar vortex” all over it. That’s slightly incorrect, because there is always a polar vortex. It’s a rotation in stratosphere over the far northern latitudes, and it influences the weather pattern beneath it. When the polar vortex is strong, it is well-defined, and the very-cold Arctic air is contained over the North Pole. The result is a “normal” winter season.
But, when that feature farther north is weaker, it can break into two or more individual segments and produce severe cold outbreaks. We saw that happen this past winter over both North America and in northeastern Siberia. The bitter cold first moved into the eastern U.S. at the end of January and refocused its center over the western U.S. in mid-February with record cold noted.
An interesting aspect of this cold outbreak is that there is a connection to the overall warming trend that Planet Earth is in. The year 2018 was the fourth-warmest year in 139 years of records. And, the past five years, 2014-18, are the warmest five years on record.
Weather extremes are to be expected with the warming trend. And, this includes outbreaks of harsh cold, even with the run of warmer global temperatures. The reason lies in the fact that the Arctic is warming at a much higher rate than the mid-latitudes or the tropics. And, this is weakening the temperature difference between the equator and the polar regions.
When that temperature difference is greater, the polar vortex is stronger; however, the Arctic has warmed so much that its ice cover is much less than it used to be, and the Arctic Ocean surface water is much warmer than the ice that used to cover it all.
In a traditional winter, the equator/North Pole temperature difference can be as much as 108ºF (86ºF to -22ºF) or 60ºC (30ºC to -30ºC). But, in this overall warmer scenario, that difference is shrinking to as little as 54ºF because of the Arctic temperatures increasing to around the freezing mark instead of around -20ºF.
This trend suggests more winters in the future having a weak and split polar vortex. The bottom line is, indications are that we will see more of these sustained outbreaks of very-cold air in future winter seasons.
Read Bryce’s weather blog at about.dtnpf.com/weather.
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