Essentially, the GFS op is managing to severely disrupt the polar vortex using in large part an Arctic High that's prominent in around 10 days time. It somehow achieves this in the face of a fairly potent stratospheric vortex, which leads to questions regarding the possible effect of the distribution of sea ice deficits, for example. These are hard to assess as it's easily possible that the op run is overdoing things.
Interestingly enough, ECM does have that Arctic High at day 10 now, which wasn't the case on its 00z op run, and there are signs that the polar vortex could split apart in the following days - in similar fashion to GFS.
The ECM ensembles don't seem to offer much help on the face of it, with a very wide spread of outcomes:
http://www.weerplaza.nl/15daagseverwachting/?type=eps_pluim
...which is disappointing as I daren't pay too much attention to the GEFS until they receive their much-delayed upgrade early next month which will bring them a lot closer to the operational in terms of the levels of the atmosphere and - I believe - the horizontal resolution.
The money remains on a zonal December for the time being but these Arctic Highs and the lack of coherent strat. to trop. coupling are starting to raise a few eyebrows in the scientific community. Just a little, but still...!
Originally Posted by: Stormchaser