Why an unusual phenomenon will cause a frigid December in the U.S.
A sudden stratospheric warming could weaken the polar vortex and trigger frigid Arctic air to spill into parts of the United States in late November–December.
Abnormally hot days may hit Australia's south-east after rare sudden warming over Antarctica
Rare sudden stratospheric warming over Antarctica could weaken the polar vortex and increase the likelihood of warmer, drier conditions in southeast Australia.