The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
BUT first lets deal w/ the N PAC signal since its been the main topic of discussion in various sectors the past several weeks. In doing so, let’s REWIND back to the MAY-JUL period 2004.
Notice how the N PAC SSTA configuration is HIGHLY supportive of a +PNA and –EPO pattern w/ the cool pool centered near 40 N / 160 W and the warm pool east of 150W and N of 30N in the GOA. w/ this setup in place the ridge would develop in the means near 60N / 145W allowing the trough to set-up over the central US.
This is one of the reasons for the RECORD warmth over AK and western Canada during the early spring. Under normal circumstances the Aleutian low contracts during the spring as the seasonal position of the westerlies lifts northward—thusly, the PNA is virtually absent during the period; however thanks to this particular SSTA configuration it was quite evident and dominating during the MAY-JUL period.
Why is this significant? It would appear to me there is a strong positive correlation between the MAY-JUN N PAC signal and that of the following winter. e.g., if the N PAC signal in MAY-JUN of a given year favors a +PNA pattern, the E PAC signal the following winter will do the same. This has worked in EVERY year which I have studied from 1856-1890 except for two--1869 and 1889.
MAY-JUN 1869:
Winter 1869-70
MAY-JUN 1889:
Winter 1889-90
As you can see the EL NINO of 1889 declined and La Nina conditions developed during the winter of 1889-90. The same occurred in 1869. This leads me to believe the reason why the correlations didn’t hold up for those two seasons is b/c the ENSO phase reversed. As you know, LA NINA conditions favor the opposite set-up over the N PAC which ties into the reason why LA NINA events are associated w/ a persistent RNA pattern and +EPO. In the years which DID work EL NINO conditions were prevalent.
We may be able to conclude that since the EPAC signal during the late spring and early Summer 2004 was such that it favored a +PNA/-EPO pattern that the aforesaid pattern will once again develop as we head into the winter GIVEN the fact that El Nino conditions (Albeit weak) are still present. Recall in the years where this did NOT work, the EL NINO decayed and the ENSO phase changed.
Over the past week or two we’ve already seen these changes take place, however we aren’t quite there yet. As of today the warm pool is still located near 45N latitude / 150 W longitude.
https://www.fnmoc.navy.mil/products/NCO ... nomaly.gif
The warm pool at the beginning of NOV was located WEST of 150 W; near 40N / 165W
https://www.fnmoc.navy.mil/products/NCO ... nomaly.gif
it is making headway ENE and eventually once it gets into the region bounded by 45N / 145W the pattern will begin to change since the ridge would develop along the west coast of NA, NOT in the GOA or near the Aleutians as it is now. The CURRENT location favors the mean trough position over the Rockies and Western plains it would indicate a weak to moderate SE ridge. This is where the NAO comes in since the appearance of a 50-50 low (or a strong/southwardly displaced PV) in combination of the block would act to suppress the height field along the east coast thusly killing the ridge even in spite of the fact that the long wave trough position is over the Rockes/Plains.
The trough position over NA this fall has moved in tandem w/ the variations in the N PAC signal—where when the warm pool was located W of 150W the ridge was near the Aleutians and the trough in the means over the West. Now that it has migrated eastward the ridge and trough positions have also.
D8-10 European MAY be showing the first signs of an Aleutian low and slightly +PNA pattern, however it would take at least a week or two for the pattern to completely reverse to one which is favorable for the mean trough position over the Central or EUS. The block development over Scandinavia is also critical b/c if it were to retrograde westward to Iceland and Greenland it would send the NAO negative. This takes us up to the week of DEC 15-21. Still no signs of a Caspian connection though near 70E in Asia.
The pattern AFTER the week of DEC 15-21 should be one which is more conducive for a EUS snow event.
