I've been quite pessimistic re: potential Greenland/sustained blocking that has been appearing on the models, I'll try to explain my reasoning why I think this projected blocking will "fail". This is a thread.

Models are currently dealing with the uncertainty of a +EAMT next week, these events often throw the models into a temporary "chaos" where errors at longer lead times increase. Coupled with that, we've got a huge Scandi high descending into China late week 2..

..which will possibly lead to a +PNA event either towards the end of this year or early January. The AAM is expected to fall through the floor. On top of this, we've got on-going strat disruption in the form of strong wave-1 activity how will this impact the troposphere?

Winter storms across N America/Canada are also throwing the models into a spin, how/where they form & track depends on how much ridging gets thrown up ahead of them, and subsequently how much blocking we see in the Atlantic/Greenland area. Next, we have the MJO;

The MJO is forecast to drop into the COD which essentially means no real 'forcing', ideally we'd want to see this moving through phases 8-1 for a decent shout at sustained blocking, but that doesn't appear to be on the cards (caveat being the RMM's have been poor this winter)

The GFS, whilst the det has been consistent in building a more amplified Greenland block, the means haven't been reflecting this, however there is good support for a N Atlantic block, I don't think there is any doubt in the northerly potential xmas > new year..

The EPS are similar to the GEFS in that they have a good signal for blocking out in the Atlantic however little support proper Greenland blocking, even the EC Det (up to todays 00z) hasn't been going for a GH, albeit a slight shift towards a more amplified Atlantic block recently

So to sum up;

- A few events on-going are likely leading to more errors in the shorter term which have big impacts in the longer range

- No real tele-connective support for true Greenland blocking

- No EPS/GEFS support for proper UK cold.

Given the above, I would expect the models (the GFS Det mainly) to begin backing away from the Greenland blocking scenario in the next couple of days with a focus becoming more weighted towards an amplified Atlantic block (perhaps temporary before it topples)

The 12z GEM actually is a perfect example of how I expect the pattern to evolve.

Atlantic block instead of a Greenland block.