Today's update to the ECMWF extended-range also shows the development of a weakened stratospheric vortex from the second half of December onwards (recall Nov run of SEAS5 predicted a weaker-than-avg vortex for Jan). The key period seems, again, to be around Dec 15th. https://t.co/3TU33BOLSn pic.twitter.com/aVJxAZn30l

— Dr Simon Lee (@SimonLeeWx) November 26, 2020