SECL -- but NOT a SECS

In the most prominent feature in the weather maps today here at midday is the massive low pressure area in the central Plains... along with the heavy snow over eastern Colorado... Northwest Kansas western Nebraska along with the heavy rains to the east.
I am mentioning this feature because of what the last few runs of the operational GFS have been showing with regard to the next system which drops into the Southwest and closes off as a 5h cutoff Low.

If you recall the medium-range models from last week most of them had the CUURENT Plains Low coming out of the Southwest yesterday tracking across the Delta and into the Southeastern states then tracking off the Atlantic Coast. Then the MR models showed a new shortwave -- A KICKER -- would come over the flat Ridge in the eastern Pacific... then drop SSE into the Great Basin while the closed 500 low started to track east. With the new system dropping SSE into the Vegas area... the SE ridge from hell re-exerted itself ... and thus the closed 5H low coming out of the SW states was FORCED over the ridge and hence a NE track into the central and upper Plains .

However now the focus is on that "kicker".... the new s/w that crashes into the Pacific Northwest and drops SSE Friday and Saturday. The 0z 6z and now 12z theOp GFS all take that new clsoed 5Low over the to the SW states due east... across Lower TX thru th Deep south and into / UP the East coast.

First let me assert that I'm not certain about this scenario we are about to discuss. From this point on I am operating on the assumption that the OP GFS models are correct with track of the 5H low and that a new or undiscovered s/w does NOT come in from the Pacific and drop to the Rockies . IF that were tio happen -- IF --- it would n turn would causes this 5H Low to track NE... just like the current Plains Low.

That being case -- again operating from this critical ASSUMPTION -- the synoptic set up at 0z 6z and 12z is a classic Text book case of WHY this East coast Low on 12/26 and 12/27 can ONLY be a RAINSTORM for the BIG cities of the Northeast / I-95... and WHY certain features must be present BEFORE the Lowe reaches the coast. To drive home the point even further this is a TOTALLY different situtation from the 11-13 FEB 2006 HECS event.... where the issue was which AREA was going to get bommbed with heavy snow and which areas were NOT. In this upcoming event there are NO such questions with regard to the Big cities of I-95 seeing heavy snow. Its not going to happen. Period.

Lets start off with the 5H synoptic set up from the 0z Models . At 96 hrs we see the 5H low in the SW with one s/w moving thru MN and the western Great Lakes ( GL) and a NEW s/w coming towards the Pacific NW. THis is feature I am worried that the models are missing or not handling right and it might drop into the Calif or Great Basin as I discussed above.

In any event by 114 hours on the 0z op GFS the s/w that was passing through Minnesota and a 2nd s/w is passing thru the Northeast as well. This does dump some cold air into the Northeast. But as you can see simply by looking at these maps there is absolutely nothing DOWN stream -- over se Canada or in the NW Atlantic that is going to cause the northern streams to slowdown. As a result the High-pressure systems which moved into the Midwest Northeast will quickly slide out to see as any sort of Southern stream system comes north.
http://www.nco.ncep.noaa.gov/pmb/nwtest/analysis/namer//gfs/00/gfs_500096114_s.shtml
http://www.nco.ncep.noaa.gov/pmb/nwtest/analysis/namer//gfs/00/gfs_500120138_s.shtml
By 120 hours we have all the ingredients with regard to the classic setting Over the Midwest for significant winter storm on East coast. In other worda the UP stream features look to be pretty good... with a discernible powerful s/w in the northern branch and we have a large closed ULL over eastern TX. 850 temps over the NE seem to be easily cold enough to support a major snowstorm.
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/00/fp0_120.shtml

Between D5 -D6 the operational GFS develops a very strong and important closed 500 low over Southeastern Canada which is often referred to as the 50/50 Low-- the upper low is located near 50 degrees north latitude and 50° west longitude. This is a very important feature for the development of a possible East Coast snowstorm pattern but there are other features problems with his overall set up. Note that the s/w that was over MB and ND is now plunging into the Midwest and beginning to PHASE -- merge -- with ULL coming out of Texas. However this is occurring too soon and as a result the 850 low and a surface low is going to take a track in land.

One of the primary reasons why this phase occurs WEST of the Appalachian Mountains... which is very bad news for snow lovers in the Northeast big cities but very good news for snow lovers in the Appalachians and potentially the Ohio Valley... is that there is NO polar vortex situated anywhere North America!!!. The position of the PV often sets up where the mean TROUGH position is going to be located.... so in this case IF we had a typical garden type late December PV over say Hudson's Bay... the mean trough would be set much closer to the East coast so the PHASE between this strong S/W in the northern branch dropping into the Midwest and a Southern system would occur further east which in turn means a better chance for more winter precip in the BIG I-95 cities. http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/00/fp0_144.shtml

Ya follow? Note that D6 the model does NOT close off a 850 low of but it IMPlIES one over southwest VA... and by 156 the 850 Low is over PHILLY whicvh is way way too far inland for snow in the I-95 cities.... its good track for heavy snow over western MD WVA western PA and central NY regions. By 168 hrs the rainstorm is over in se New England
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/00/fp0_168.shtml

Of course it's a possible that as the 500 low tracks Northeast the rain could flash over to snow and the 0z Models DO show really good wraparound snow and snow showers over portions of western MD Northwest Virginia Western Central Maryland eastern PA much a Southeastern New York and a good portion of the New England. Wrap around snow is better than nothing... BUT it aint real snow...

The op 6z GFS...
again we can see a really good synoptic set up occurring UPSTREAM over the Midwest as the two streams are phasing very clearly at Day 6. But as you can 850 Low is in a HORRIBLE position... well inalnd... and this is even more critical than normal because there is no sustained arctic flow or Cold High to the north. As I have already stated ....and as I am sure you are aware of... we are NOT seeing any sort of amplification in the northern branch over western Canada. Thus there is NO real cold air source to come south when the northern branch begins to amplify. As result even though we have a pretty good phase here at Day 6.5 the only air mass we have to work with is a Pacific air mass. And when you have any 850 Low that is so far inland .... well you are toast. It's just not going to happen with 850 track
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/images/gfs_500_144l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/images/gfs_850_144l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/06/images/gfs_500_156l.gif

The 12z OP GFS... is consistent with the last couple runs in how the overall set up is going to affect the surface track and the 850 low. At 120 hours the model is clearly showing the phase is occurring even FURTHER to the West and temperatures at 850 are much warmer on the 12z run for 12/25 than what we saw on the 0z run at 132 hrs!!!

And 132 hours the model has developed a closed 500 low over the Southeastern states and again that is fairly consistent with the previous runs and with what we are seen on other models.
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/fp0_120.shtml
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/fp0_132.shtml
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/fp0_144.shtml

As you can see the 850 low is now west of Roanoke Virginia and tracking NE which is a disaster if you like snow in the I-95 corridor. Note how the zero isotherm at 850 is well West of I-95 cities and 850 winds are 30-50 knots out of the SE. By D6... the 850 low is NORTH of NYC and still tracking and almost all of se New England is getting strong SE winds at 850 and winds at the surface.


http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/images/gfs_850_132l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/images/gfs_850_144l.gif

The 12z GFS ensembles are showing very much the same sort of thing with no source of cold air to dumping to the system and no changes over eastern Canada would force the phase to occur further east. The operational midday Canadian at D6 is showing the same sort of thing with the phase occurring over to the WEST of the Appalachians which is just not a good sign for folks who want winter weather in the big season the Northeast. It is of course a pretty good sign for the mountains of the Northeast... the Appalachians.
http://weatheroffice.ec.gc.ca/data/model_forecast/colour_images/12_054_G1_north@america@zoomout_I_4PAN_CLASSIC@012_144.jpg
Finally here is the midday European and we can see at D5 the kiss of death here... note how the northern branch is now phasing with the Southern system over the Mississippi Valley which is significantly further WEST than what we were seeing on the earlier runs the European. It is also supportive of the trend that we are seeing here midday WED with the other models such as the 12z GFS as I have already discussed.... such as the midday Canadian and the midday UKMETl. Of course this is all assuming that these medium-range models are fairly close to reality here at Day 5. I believe they are because most of them are showing the same sort of thing and the same trend here at midday.