0850 GMT October 15, 2019
The culprit, as it appears, is the polar vortex which allows the flow of arctic air from the north to move southward. The zone of colder than expected winter temperatures, named the US warming hole, sits over the Southeast through spring until it migrates to the Midwest during summer months.
Warming temperatures in the Arctic and melting of Arctic sea ice appear to initiate the movement of the polar vortex southward through a wavier shaped jet stream. The Arctic has warmed twice as fast as the northern mid-latitudes, setting up an imbalance in global circulation, forbes.com wrote.
The temperature difference (gradient) between the high latitudes (Arctic) and mid-latitudes (Southeast US) traditionally acted as a boundary to keep out the polar jet stream. As temperatures disproportionately rise in high latitudes, that boundary is weakened and polar winds are able to escape southward easier.
While counterintuitive, the cooling of the Southeast US during winter months is, in fact, due to a globally warming planet. This is yet another unforeseen consequence of how global circulation patterns will react to changes in Earth's insulation (i.e. heating).
The study found that the jet stream has become wavier since the late 1950's, coincident with the timing of cooling in the Southeast US during the winter.
The recent extreme cold snaps in the Southeast, which seem counterintuitive to global warming, may be related to the US warming hole, said Trevor F. Patridge, the lead author in the study from Dartmouth College.
The warming hole in the Southeast US then migrates to the Midwest during summer months, causing cooler than expected temperatures during prime crop months in the breadbasket of the United States. These results help to define how we manage expected temperatures in the years and decades to come.
The warming hole has led to a 1.2°F cooling over the Southeast US during the winter since 1958, compared to a 1°C warming globally. Don't like winters? The Southeast US will likely continue to have colder winters with more snow/ice. This has large implications for city planning in the Southeast and will continue to impact productivity in everyday lives. In addition, the agriculture industry in the Midwest will continue to grapple with colder than expected summer months, their growing season.
As expected, changes in our global climate have unforeseen effects on other parts of the world. These will continue to be challenges as we grapple with how to manage the unintended effects of climate change: Flooding, drought, wildfires, hurricanes, etc.