A classic case of amplified North Atlantic anticyclonic wave breaking building the Ural high in this GFS forecast [graphics: @HannahAttard]. The pattern amplifies wavenumber-2 and kick-starts a wobbly (technical term) period for the stratospheric vortex... pic.twitter.com/8Hpk0HWF9l

— Dr Simon Lee (@SimonLeeWx) December 1, 2020