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Back in late OCT I stated that we should slowly ease into the expected winter pattern (discussed in the winter outlook) during the later half of NOV and into early DEC. that idea seems to be holding up.
What has been precluding the development of a decent winter pattern over North America is fairly straightforward.
1. The SSTA configuration over the North pacific which supports a strong pacific jet and western US trough (RNA pattern) has to reverse. Right now it is the opposite of what we saw two winters ago in the NPAC which screamed persistent PNA pattern and EUS through.
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
https://www.fnmoc.navy.mil/products/OTI ... nomaly.gif
2. The Absence of ridging near 70E in Asia has prevented the PV from moving over to our side of the Pole. As long as remains the case, it’s hard to get a winter pattern to develop over North America. Simply put, heights remain anomalously high and temps run above normal in the means.
Remember The POLAR VORTEX (PV for short) is analyzed at h500 and is the core of the coldest air found in either the northern or southern hemisphere. For our purposes we will take a look at the northern hemispheric PV. Cold air is more dense and compressed, so it has a low thickness (we will use 1000-500mb thicknesses for this example). The density of the cold air causes heights to fall and thusly the reason why lower heights = colder temperatures, lower thicknesses, and higher heights = warmer temps and higher thicknesses. So b/c the cold air is very dense and has a low thickness, heights at h500 will lower. The center of the lowest heights and temperatures in the northern hemisphere is regarded as the PV. The PV moves in the direction of arctic airmass. At the surface however a polar airmass is represented by high pressure.
3. +EPO pattern. This is associated with a north south dipole of anomalous heights over the pacific basin. In the positive phase, below normal heights are found in the GOA w/ a center of opposite sign near Hawaii (ridge). The resultant effect causes an intensification and eastward extension of the pacific jet.
On the positive side, the STJ is still alive and kicking w/ the snows over the western low plains, TX, NM as you might expect to see since the SOI is negative (and perhaps headed for the tank again over the next few days) as it should be w/ the weak EL NINO in place.
Whats interesting to note is the persistent trough over extreme southeastern Canada and the NW Atlantic that had been recurring quite a bit last month and the first part of this month. That may be a critical this winter, but in the short term, it has helped to cool the SSTs off the east coast thanks to the continual NW flow and upwelling taking place.
The new 12z ECMWF from today is showing what looks to be the beginnings of a large scale pattern change which it has been advertising for the past few runs.
http://vortex.plymouth.edu/gifs/041114013213.gif
The first thing of note is the DUAL PV, with one center along the Siberian Arctic coast and the other center developing on our side of the pole—NW of Hudson bay near Baffin Island.
The ridge up along the North coast of Alaska (which is what became of the bock that retrograded westward and from Greenland and now reemerged) is helping to anchor the development of the new PV, plus aiding in what looks to be a cross-polar connection in the developmental stages. The ridge is also showing signs of popping up east of the Caspian.
Thirdly, were seeing another cutoff trying to form off the west coast of CA. this is critical since the ridge gets pumped overtop of it due to the positive tilt to the trough and would setup another REX BLOCKING pattern off the west coast. That would force the jet to split (split flow over the east pacific) and the trough to come back into the EUS. The PV setting up in Canada would suggest that there is cold air present and waiting to be discharged—a cross polar flow would make it worse. Moreover this would help to develop a more defined Aleutian low.
Lastly—the trough is headed down into Scandinavia so w/ the PV forming on our side of the pole, and signs of a 50/50 low (albeit displaced somewhat east of its climatological position). If this is the case, the ridge would amplify toward Greenland and send the NAO negative.
Supporting this are the 00z 11/13 Canadian ensembles
http://www.meteo.psu.edu/~gadomski/ENSC ... z/f240.gif
The GFS ensembles from 0z are all over the place in general, but a few members do seem to be jumping on the ECMWF idea. Notice the PNA ridge present on some of the members. One even has an omega block developing in western Canada.
http://www.meteo.psu.edu/~gadomski/ENSHGT_0z/f252.gif
The 12z runs were even more disorderly WRT the pattern evolution over the EPAC, but DO seem to be picking up on the development of the PV in North central Canada.
http://www.meteo.psu.edu/~gadomski/ENSHGT_12z/f240.gif
And for laughs, the 12z Operational run of the GFS:
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_192l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_216l.gif
Has the PNA ridge, and PV. Now let’s see if it holds on to it.
As far as the teleconnections go, the Ensembles are indicating a –AO developing toward the end of the period but if we look at the verification, they have not been doing a great job over the past few weeks—especially in the long range.
http://www.cpc.ncep.noaa.gov/products/p ... .sprd2.gif
PNA is forecasted positive, which is pretty likely especially w/ the development of the rex blocking off the west coast.
NAO:
http://www.cpc.ncep.noaa.gov/products/p ... .sprd2.gif
Again I want to stress the fact that the GFS ensembles have been doing a reprehensible job over the past few weeks from 10-14 days out, so it’s important to see if there is support among the other models before buying these solutions.
Looks unclear at this moment for who, if midwest, northeast or like you said maybe both. Should get more clear in a week or so.
