Several of us have mentioned in the last week or so that the models were hinting at a flip in the NPAC. Well the overnight runs in the extended I believe do show the lead into that possible flip.
Below we have the verification for Dec 4th which is shortly before we saw a flip to the long duration strong +PNA/-EPO combo. Now the features I want you to notice are the higher heights towards the pole (B) with ridging (C) extending towards it up off the west coast and into Alaska. We also have a portion of the PV (D) located in north central Canada with troughing (E) extending from it down into the southwest. The key feature here is the strong PV in the NPAC (A) which I believe initiates the flip. What we have seen in the days before this snapshot below is that the pv begins elongating and shifting eastward from the western Pacific where it was originally situated to where we have it now into the Aleutians. This in turn is forcing the ridging/higher heights (C) northward as it gets squeezed by the trough into the southwest.
Now compare the above to what we see below on the 15 day EPS. Remarkable similarities between both maps. We again see the higher heights over the pole (B) with a pv (D) located to the south in NCentral Canada. We also see the ridging (C) off the west coast building northward into Alaska with a trough (E) into the southwest. The initiating feature once again is the PV (A) as we have seen it elongate and shift eastward into the Aleutians.
Not to be outdone the GEFS at day 15 is almost spot on with the features on both maps above and it too shifts the NPAC pv eastward into the Aleutians.. About the only difference we see is it is a little weaker and more progressive with the SW trough so we are not seeing the ridging/higher heights building to the extent that we saw on the previous two examples.
Now one other thing I want to bring up is the eastern half of the globe on the maps below. When taking into account smoothing we see occur on the extended ensembles, which lose the finer details especially at the mid latitudes, and the fact that there are some slight timing issues with some of the features, the similarities match up extremely well. I can never recall having one model run match up so well in the N-Hemisphere to a previous verified time. And yet here we have two and both timed at 15 days to boot.
And here we have what verified two days later, Dec 6. The NPAC has flipped and we begin the long duration +PNA/-EPO. We also see the pv drop southward into southern Canada and the higher heights in the east forced into the NAO domain where we then saw a predominately -NAO for roughly a week. For those that can recall I was very high going into this period even considering climo for early December. We in fact did see a roughly 9/10 day stretch where some made out fairly well for so early in the season. The one thing that did limit our potential was that we saw the pv/associated mean trough located a little too far to the east for our region.
Give me this and the following 10 days we saw, with better climo and the pv/trough located a little farther to the west and I think we do much better then what we saw in early December. Who knows. Maybe even WOOF worthy.