Corresponding tropospheric forecasts in week 3 & 4 from CFS show enhancement of mean stationary wave field, including persistent Scandi-Ural blocking & Aleutian Low. For a while there has been indications that ~Dec 15th might be crucial for strat evolution & this is supportive.
Things to look out for include anticyclonic wave breaking in the North Atlantic helping to build the Scandi-Ural block & enhance vertical wave flux. Also watch out for the vortex to consolidate polewards with a sharpened vorticity gradient on its edge. MJO also important.
There remains large spread in the long-term evolution of the vortex - which may suggest there exists a critical moment where the subsequent state is sensitive (think of wings of the chaos butterfly), perhaps to both the state of the trop & strat at that time.
Check out this forecast for December 12th... could it be part of the apparent divergence point of uncertainty (see earlier threaded tweets) regarding the longer term stratospheric evolution? Maybe...
