2019 began with a major sudden stratospheric warming, with the #PolarVortex splitting in two.

2020 is set to begin with the opposite! An intensification of the vortex, with strong westerlies descending in the GFS (after a briefly weaker period due to amplified wave-2). pic.twitter.com/eHrHdPoMls

— Dr Simon Lee (@SimonLeeWx) December 22, 2019