“The Chicago freeze of 2019 actually began when warm air from Asia found its way up into the stratosphere and forced the normally stolid polar vortex to dissociate into lobes—one of which wobbled down over North America, taking a deep cold meander of the polar jet stream along with it. Called arctic outbreaks, these displacements appear to have become more common in the last half-century, for reasons that researchers are still working to resolve.” Hint: global warming, also great argument against deniers of kind “it’s cold now, where is the warming?” - It is above cold layer, actually displacing it downwards