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the 1st issue to deal with is the s/w coming out of the sw states into the Lower Plains and Midwest this weekend and what it means for East coast with regard to Sunday and Monday.
There are some important changes in the midday models very early in the medium-range period -- Sunday night and Monday. The first major change is that the arctic HIGH which comes down after this cold front on Friday and Saturday does NOT drop y into the Lower Plains and instead it stays across the central Plains then heads into the Great Lakes and New England. This means that the cold air is going to be further north and the threat for significant snow and ice over Central and the lower portions of Texas as well as the upper Delta is greatly diminished. NM OK and north TX as well as MO look to see a good snow.

In addition most of the short-range models now show that the shortwave comes out of the Southwest further north. Yesterday that was taken a system to Missouri now it takes that of the northern Missouri Southern Iowa and very close to Chicago.

The primary reason for this shift has to do with the southeast ridge and eight another stronger shortwave which drops down from Weston Canada along the Rockies into Arizona and New Mexico this weekend in early next week.

Because you have one piece of energy dropping from north to south ...that is to say from the northern Rockies into the Southwest states you HAVE to get a corresponding reaction to the flat Ridge over the Gulf coast of Florida and that reaction will be to see the southeast Ridge expand a little to the north.

As a result the threat of winter precipitation with a system for the Tennessee Valley and lower portions of both NC and northwestern SC is greatly diminished in my opinion. Oh there maybe some BUT it does not look like a big deal at this point.

the model trend is clear to me... the strong s/w that comes out of the sw state that then gets crushed once it reaches Mississippi roiver is going to develop NOT a east coast Low per se... but it is an over running.

It is time for Me and others to make clear that this Sunday night Monday is NOT a coastal Low or major snow ... The only reason this event is going to be SIGNIFICANT is that its the 1st one of the season...

Not surprisingly the mid day Thursday GFS of courses screws this up since the cold air bias makes the model essentially useless this far out in time. Even though we can clearly see that the shortwave is now further north than what the model was showing yesterday and the Ridge over the southeast a little stronger somehow or another the model still takes the surface reflection of low well south of Cape Hatteras which of course makes no sense in all.

Actually I think the midday Canadian is probably the best are most reasonable with this solution regarding Sunday night and Monday
http://meteocentre.com/models/gemglb_amer_12/gemglb_amer_12_panel.gif


The next major problem have to deal with is that big shortwave I talked about above dropping into the Southwest states late this weekend and early next week. It certainly has the potential to bring another significant snowstorm to the central Rockies as well as a Denver area But the issue is that the MR models are having real trouble figuring out what to do with the shortwave.
http://www.nco.ncep.noaa.gov/pmb/nwprod/an...2/fp0_096.shtml

For example the midday GFS has another piece of energy coming in on the northern branch which ends up crushing the shortwave in the southern branch and we end up with a sheer ZONE axis ... in a SW to NE direction tracking through the Deep South and Tennessee Valley. This means that the only wave / LOW development can occur over the Florida Panhandle or perhaps far southern Georgia and the low scoots out to sea by the end of Next week
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/fp0_144.shtml

as you can clearly see from this map at 144 hours... IF the southern s/w were to come out intact and NOT get sheared apart AND we do in fact have that next strong shortwave in coming down from Central Canada in the northern branch... the potential exists for significant winter storm on East Coast. I am confident that the operational GFS is ripping up the southern system too rapidly and therefore I reject the solution as shown on the Thursday midday operational GFS.

In addition most of the GFS ensembles which also still have the cold bias are mishandling this southern shortwave so most of their solutions are not viable in my opinion.

However the midday European does not have this problem and since it handles systems on the southern stream far better than he GFS we end up with a phased development.
The European keeps the coastal ffront which develops from the Monday system along the Southeast and middle Atlantic coast . Because the model handles the southern system differently we end up getting a significant coastal Low that forms late next week. Of course the issue is how close to the coast will this Low form and will there be enough cold air in place? None of those questions can be answered at this time but because we do have a split flow pattern and we are going to have a significant shortwave hanging back in the Southwest that will come out in SOME form or another the next several days has to be watched very carefully for the potential for winter storm on the NE Coast.

It is also possible that the system in the southern stream might get ripped apart and if that is the case we will end up with a Clipper system moving thru with a reinforcing arctic cold front
the other aspect to the potential for the storm on East Coast late next week is that this Low has major implications for the overall pattern in the last week of January and into early February.... and in particular which model is correct in terms of the Arctic blast after the 25th January.
As you know the last few runs of the operational European as shown a severe arctic outbreak developing after January 25 with the Arctic Airport in all liens isn't the Deep South and 850 temperatures as low as minus for driving into Central Florida.

The European model is doing this because the development of major Low the East Coast that moves into southeastern Canada LOCKs the Eastern trough positioned in place over the eastern half of the CONUS which results in a much colder pattern. That's the next strong arctic high that develops a Weston Canada does not plunge down East southern Rockies but hates into the Midwest and East Coast. The midday European model continues the trend from the last couple of days and develops a bitter cold Arctic air mass that plunges deep into the central and eastern CONUS... with below freezing temperatures plunging into Central Florida by Day 9-10!!!

On the other hand the midday Thursday op GFS does NOT develop a significant NE Low late next week... so the trough over the East Coast is able to slide further off the coast and the pattern is able to relax a little bit in terms of the cold air eastern Mississippi River.

In the week 2 time frame the midday American model Has a couple all the transient troughs that swing through the eastern US with some cold air on Day 10-11 then relaxes the trough of bit only to rebuilds the trough day 14-15 with a severe arctic blast over the eastern conus.
Which one do I think is going to be correct? At this point I don't know although I am far more likely to lean towards the European because as a general rule the European does better with Storms on East Coast and because the GFS solution which is to crush the shortwave in a Southwest when it comes East is most likely not the correct one. It's possible we may getting a big Low in the west of Atlantic similar to what the European are showing ... just a little further to the east. This would still lock the trough in place over the East Coast provided the ocean low would move up into southeastern Canada Labrador.