Today's 00Z GFS is a pretty extreme solution in the troposphere (*huge* -NAM) but the stratospheric evolution follows on from recent runs, only ramped up - reversing the U winds in the upper stratosphere in early Jan, with significant warming at 10 hPa. Minor SSW territory... pic.twitter.com/1lxA3Rh96f

— Dr Simon Lee (@SimonLeeWx) December 18, 2020