Winter of 2019-2020 was a very mild winter when compared to the blasts of Arctic air we saw in January 2014. The reason for this mild winter can be attributed to the polar vortex. One question you may be asking yourself is what exactly is the polar vortex and how does it affect whether we have a mild winter or not? The term polar vortex refers to a cone of low pressure that sits directly over the poles. The polar vortex is made up of a fast-flowing stream of air that envelops the North Pole.
The polar vortex is strongest in the winter due to the increased temperature gradient between the mid-latitudes and the poles that, in turn, strengthens the jet stream. This takes place in the stratospheric layer which is typically around 6 to 30 miles above ground. When the polar vortex is the strongest, all the cold Arctic air is trapped at the poles, but when it starts to weaken, Arctic air will plunge into North America or Europe. For much of the winter of 2019-2020, the polar vortex has remained strong which has kept the CONUS warmer than average.
(Image Credit: NOAA)
The image above shows that during a stable polar vortex like this current Winter all the cold air is contained to the north; however, when the polar vortex starts to collapse cold air will move south while warm air moves to the north causing a wavy polar vortex to sweep across North America or Europe. The wavy polar vortex will produce blasts of cold air as the pattern progresses across the Northern Hemisphere. This trapping of Arctic air in the polar latitudes has allowed record heat to dominate over colder temperatures for the last part of 2019 and first part of 2020.
According to the Weather Channel, the polar vortex should remain strong at least through March. This means the CONUS can expect above average temperatures this spring.
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©2020 Weather Forecaster Hannah Peters