CFSv2 week 3 & week 4 500 hPa height anomalies now suggesting negative NAO pattern/Greenland blocking. This North Atlantic weather "regime" is very sensitive to stratospheric vortex strength, and occurs more frequently in weak vortex states (not just after major #SSWs!). pic.twitter.com/Uixv2TqXrd

— Dr Simon Lee (@SimonLeeWx) December 20, 2018