Pac NW to get battered for at least another week; +PNA to develop after 12/20

Assuming that I'm up and about at a reasonable hour in early in the morning I will endeavor from on to have this plot updated everyday by 730 --800 am EST ( weeekend somewhat later).

There really is not much to change in the next five or six days with how this is going to unfold from the current mild pattern back to a +PNA pattern by DEC 22-23 . The first important piece the puzzle is going to be the songs shortwave which crashes into Seattle or lower Vancouver Island Thursday night and races east along the US Canada border ... tracking north of the Great Lakes on Saturday and Sunday. This is an important feature because the trailing cold front is going to drive south and east across the Upper Plains the Great Lakes and into New England . This front will then probably come to a halt in a sw to ne direction 12/18-19 roughly on a line from eastern Texas thru the Upper Delta... very close to the Ohio River then close to the Mason Dixon line. The European i & Canadian models develop a weak wave of Low pressure on the front while the operational 0z GFS and Ukmet do not. This wave is going to the first forecast problem to deal with in eastern US because if that wave does actually develop we may see some overrunning when to whether north of front across portions of Ohio Pennsylvania and New York.

Longer term the problem is what happens in the southwest US. The operational GFS this morning at Day 7 has a deep close ULL over the southwest which comes about because the models biased to over phasing systems. The energy from the northern branch in western Canada faces and the model develops the ULL too far west on the 0z run. This is in stark contrast to the operational 00z European and Canadian which do have a close the 500 low over the southwest but those models have the closed ULL significantly further east and they do NOT show a CUTOFF Closed ULL. This implies the 500 low in the SW is going to be a lot more progressive than what the operational 0z GFS is showing.
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/00/fp0_180.shtml
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_180.shtml



The 0z GFS ensembles do NOT support the 0z GFS operational run... but do strongly support the European Canadian solution. Really this should be a TEXT BOOK case where one should be looking at the ensembles rather closely... whenever you have a synoptic situation where there may or may not be a close to 500 Low hanging back over the southwest then the ensembles really have to be used very heavily as operational medium and long-range models have a tendency of screwing up the solutions pretty badly.
http://www.meteo.psu.edu/~gadomski/ENSHGT_0z/f180.html

Obviously this is important because if the system it does hang back as far to the west as the 0z GFS is showing dandy rage over the Southeast is going to be significantly stronger and a cold front is delayed at least a day may be to perform reaches East Coast. As a result the 0z GFS doesn't have a cold front reaching East Coast almost the 24th whereas the operational European and Canadian are much faster.

Taking a look at the 6z op GFS we see a much more realistic run that is a lot closer to the GFS ensembles mean as well as the operational European and Canadian. You going to see me refer to this as a RULE many times this winter and even to the summer months but whenever the 6z operational GFS turns around and shows a solution that is similar to the 0z Euro it's a pretty good sign that the European solution is more likely be correct.

That is not to say I do not have a problem with the operational European this morning at D7. I most certainly do. Usually when a clsoed and cutoff 500 Low forms over Bja Calif or NW old Mexico the s/w energy drops down along the west coast of North America then along the coast of California. But in this particular case the model forms that piece of energy on D6 which gets left behind and then intensifies and retogrades. This sort of development is not really supported by the European ensembles is morning. On the other hand I do liked what the European Day seven is depicting that shortwave moving through the Great Lakes and ushering in a reinforcing shot of colder air across the Northeast.

No matter which model you prefer the key point here is that by Day 7 the overall pattern shifts from a unified flow into a split flow with two distinct branches.... and that always leads to some interesting whether in the winter months especially when you have a Moderate El Nino.

What happens by Day 8 & Day 9 is that the operational European develops a a strong ridge in the Northern Branch which allows a shortwave to drop and amplify into the Plains states as the southwest low comes out across southern Texas. In this situation if we could keep a 50/50 Low in place then we would have a pretty good shot for a significant storm on East Coast say 12/23-24. But the operational European doesn't show the 50/50 Low over NF holding so as a result when the two systems meet or "Phase" it occurs to far to the WEST to be a East Coast winter storm and instead we are looking at Appalachian event where places like Pittsburgh Columbus Ohio West NY state and even Greensburg PA could see significant or even heavy snow.
By 12/24 we are back into a full bore +PNA pattern with seasonal cold over much of the central eastern US and many the models showing some sort of significant storm thread on Christmas Day. Taking a look at what say the 300 hour 0z GFS ensembles either dropping into the Plains states and/or head towards East Coast... C001 p002 p003 p007 p008 p009 p010.

I've particularly liked the 6z GFS idea at 288 hrs...
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/fp0_288.shtml

Last point I want to make regarding good feedback question I got yesterday regarding the pattern. Earlier this season and in my winter forecast I stressed how it seemed that no matter what happened with the pattern we were getting East Coast Low to forms ... but now I appear to stressing that we are in this repeating cycle where the mean trough is forming out over the west coast we can ridge in East and pattern progresses and return cold East with several days of a +PNA forming... and arent I contradictring myself?

Yes that person has a point --I am changing little bit here because for one thing the blocking pattern we had during late September October and early November is no longer in position around Greenland. SECOND ... is that during the month of November the El Nino did strengthen from a weak event to a modern event and there is a lot of research which shows how significantly different the overall pattern to North America run between a weak El Niño event versus a moderate want..

Thus I have changed the ideas here in DEC a bit in this regard from what we saw in October and early November. Again this is a way I do thing and it is a point on which some forecasters and some weather hobbyists do NOT like. The data changes so the forecast has to change. It's not about my ego... It's about getting the forecast right and IF that means I have to change how I see things developing in this 1 portion of winter for a few weeks I do so. This is in stark contrast to some of the other forecasters out there who have latched onto the warm winter dogma and who have continued to deny that cold air at any time is ever coming and totally missed the cold outbreak we had a first week of December... and even now are way behind the eight ball this morning WRT the developing +PNA pattern we see developing in the days right before Christmas.