The November update of the ECM is now suggesting a weaker than average stratospheric polar vortex at 10hPa during December 2019 contrast to last month's update. However, the Glosea5 is less confident on this with quite a high spread especially in January. It's important to note that the Glosea5 has a better verification record than the seasonal ECM but at the end of the day, they're long range models so prone to huge changes.
Yesterday's GFS backed away significantly from the SPV getting disturbed with +AO filtering down through the atmosphere in FI whilst still forecasting quite a weakening in the zonal mean zonal winds at 60N 10hPa. The ECM showed similar but actually also showed a strengthening again at the end of FI.
Very confusing picture.