The subseasonal GEFS has a substantial signal for a strong (upper tercile) lower-stratospheric (100 hPa) polar vortex for the remainder of 2021, but particularly through the first two-thirds of December. These are the circulation anomalies that the troposphere 'feels'. pic.twitter.com/ZWlWIIXaYa

— Dr Simon Lee (@SimonLeeWx) November 30, 2021