Extreme winter weather across the United States is linked to Arctic warming, suggests an observational analysis of data from 1950 to 2016, published in Nature Communications. This is particularly pronounced in the Eastern US where extreme winter weather is two to four times more likely when temperatures in the Arctic are anomalously high.
In parallel to increasing warming in the Arctic, winter cooling trends have been observed in Eurasia and the eastern US. Whether this link is a result of global warming or natural variability is highly debated. Some observational studies have shown extreme winter weather in the mid-latitudes coincide with anomalous atmospheric circulation in the Arctic; however, those were limited to specific years.
Judah Cohen and colleagues present an analysis of observations across 12 US cities to show a link between Arctic temperatures and severe winter weather in the US dating back to 1950. One novel aspect of their study is the combination of an index of winter season weather in the mid-latitudes with temperature and circulation anomalies in the Arctic. They also show that since 1990, the frequency of these cold episodes in the eastern US has increased, but has decreased in the western US as Arctic warming has become more pronounced.
The authors note that while they do not provide a mechanistic explanation for this link, it is consistent with previous studies suggesting a weakened polar vortex drives this effect.