...stratosphere still warming...still looks like this could eventually downwell into an east based -NAO, and a -AO/-EPO. However, we'll see if this warming continues and if it eventually downwells into a 500mb block...
There are two possible issues here.
1. The development (or lack there of) of a Polar Vortex. The 12z GFS develops a big one, and displaces it due to a -NAO and HUGE +PNA into SE Canada causing by far the coldest air of the young winter...
Right now though there is no sign of a PV anywhere over the western hemisphere:
And, with an overall +NAO/+EPO/-PNA pattern persisting for at least the next 10 days I'm not sure if we'll see some sort of big storm occur that forms into a PV...right now the Euro has no signs of a PV at 240 hours, and still has a very +EPO/NAO, with a neutral-negative PNA:
And, while the ECM does have a S/W over the Plains at 240 hours, it isn't nearly as deep as the one the GFS has at 240 hours...this S/W gets pulled into the GFS's PV...there is also no sign of a deep PV over the N. Pole at 240 hours on the ECM, although it's there on the GFS:
So, big model differences at 10 days out...the GFS has a huge PV with a trough sitting over the Plains that eventually deepens as the PV becomes displaced...the GFS also has a developing +PNA at day 10 although it isn't too strong yet...the Euro is vastly different with the Pac pattern...so, getting to the Pac pattern, my next big concern:
2. The Pac jet will be ripping for at least the next 10 days. The GFS slows it down by day 16, but at day 10 the ECM shows no sign of weakening the +EPO and slowing the Pac jet down...the GFS ensemble members are different from the op in this matter as well, and do not slow down the pac jet that much either, and don't have a huge PV over SE Canada either...right now, there is some tropical forcing over the central and eastern equatorial Pacific. This may be strengthening the Hadley cell over the central/eastern Pacific and be the reason for the raging Pac jet right now...the EWP model shows this persisting for at least 10-15 days...
If this is the case the Pac jet will not slow down and allow for a huge Turkey day cool down like the GFS is showing...note that a lot of the ensemble members still show a strong Pac jet at the end of the run (FWIW at this point), and only like 2 or 3 other members (out of 11 pertributions that are different than the GFS) show a displaced PV making it into SE Canada:
The GFS (upper left) is the most negative with the NAO, most negative with the EPO, and by FAR the most positive with the +PNA...this should throw up a red flag that the cool down the GFS is continuing to show near the end of its run is very possibly complete fantasy...what may be happening is the GFS is seeing the stratospheric warming and down welling it too quickly.
So, despite the stratosphere warming there still are no guarantees of a big cool down. While the warming continues to strengthen, we don't know when the warming may downwell into high latitude blocks, and where they may occur. FWIW, the strongest warming does appear to be over western Canada/Alaska/N. Pacific. If the strong block ends up here, over Alaska/Aleutians, this could cause the cold to end up over the west/MW when the Pac jet does relax some, especially if the we don't get a Greenland block out of this. FWIW, there is some good stratospheric warming over like the Iceland/UK area, if we get a block there it may be an east based block. Again, no guarantee for cold over the east. If we get the best tropical forcing to be focused near the dateline as this warming downwells into high latitude blocking in 2-4 weeks, then we may indeed get a Greenland block to form. However, there is definitely no guarantee of that happening, and right now the pattern doesn't look good for cold, especially over the east as we end November and head into the beginning of December.
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