DT IS CLOSE TO BARKING AND LETTING LOOSE THE HOUNDS OF SNOW ..
As I go about explaining why I am about to bark I have set up key premises. Yesterday I made the following statement in the blog.... and it is really important you read it so you understand how the pattern is going to change at the end the month in such a manner so that there is likely be a significant winter storm over the East Coast of the US. Please read this statement carefully
You see the main problem have right now is that all the shortwave activity coming out of STJ / southern branch is over northern portions of Mexico and S Texas. In the current flow... and in the pattern over the next 7 days... these S/Ws cannot Gain enough Latitude so any surface development is over the Northern Gulf and the Lows end up sliding off the SC and GA in ENE direction.
However if we do enter the process undercutting the Ridge in the last few days in January and early FEB this will (as I said) establish a Split flow pattern. And more importantly the S/ws coming in across the Southwest will have enough time and distance to gain latitude as they head E or ENE . In other words IF you have a shortwave over the SE Texas that tracks in a 060 direction (ENE) it's going to slide out to sea as will the surface Low. The same track however with a shortwave which is starting back over the Southwest... well now you are in a different ball game.
Recall the weak Low that moved off the NC coast this past weekend ? Originally that Low was played up as 1st decent moderate snow for Middle Atlantic... yes several days out I did that as well. The reason? Most forecasters could NOT believe the pattern which has featured the prominent and very strong Southeast Ridge for the past 75 days would suddnely give up so quickly. But that is exactly what has happened.
That is why the shortwave which came through with the Northeast states on the Arctic front today is going to form a big Low so far out to sea because ....there is no Southeast Ridge to keep the Low closer to the coast.... That is why the area of Low pressure develops the Northeast Gulf in 60 hrs and moves off the GA SC coast in 72 hours is NOT going to climb further up the coast.... because there is NO Southeast Ridge.
The pattern change over the past 5 days has been so complete so massive and the PJ has become so dominant that any sort of Low that develops in Eastern Texas the Delta or along the Gulf Coast is quickly whisked out to sea....because we have no Southeast Ridge !!! and because we have no sustained negative phase of the NAO.
This pattern is NOT going to change unless something makes it change. We also have to keep in mind that we have no hint at all on a -NAO on any of the models. The PNA ridge is so massive and strongly positive and the flow is simply too fast to allow any sort of buckling in the jet stream over the North Atlantic to support a -NAO.
This leads to two important problem with respect to getting snowstorms for the East Coast. Right now in this pattern all the Arctic High-pressure systems are dropping down from western Canada into the lower Plains. At that point the Polar Jet tuns ENE so the HIGHs scoot across the Deep South then move off the Southeast coast. This of course shuts down the Gulf of Mexico as well as force the fronts deep into the Gulf. Low pressure areas are NOT forming over AL or TN but over or near New Orleans or in the North Central Gulf.... and in this flow that means Out to sea!!
As I stated yesterday there are only TWO ways to get out of this trap.
One way is to to have the S/Ws in the southern stream start out further WEST --- such as the Southwest states or perhaps even the Central Plains so that the same ENE flow of the PJ ....-whch has been taking these Gulf Lows off the SC coast and out to sea ... is now taking these Lows into TN and NC / VA. In this possible solution to the snowless trap for the Eastern US the overall pattern has not really changed .... what happens is st that the hypothetical shortwave which triggers the surface development is starting out further to the North and the West so it simply has more time to gain latitude.
TWO the Other solutioin is to have more and more energy coming over the top Ridge in western Canada plunging into the Plains states which forces the trough to become very deep and very powerful.... taking on more of a V shape then the broad U shape than what the trough is now in.
We can see many of the medium-range models are beginning to develop the second solution quite nicely. Here is the0z Thursday GFS at day 9 at 500 MB... and what has happened is a whole new surge of energy has dropped in from over thetop the Ridge on the West Coast of North America and has forced the trough into a large EGG shape.... with the bottom or rounded point of the EGG reaching into the central and Lower Mississippi Valley. This of course generates some sort of Llow pressure area developing over the Mississippi Valley or perhaps Tennessee Valley... but because it starts out at a further north latitude the whole system gets to track further to the North which brings the threat of significant winter to much of the eastern US.
At first glance one might argue that this pattern amplification could be an over reaction from the op GFS since it occurs after the model truncate at 180 hours and often that is when the model comes up with some thing that is goofy. However the 12z Thursday op GFS closely matches the European from Wednesday as well as the European runs from today...
many of the 0z GFS ensembles strongly supports the operational run ... pay attention to the particular members.
p01 p01 p05 p06 p07 p08 p09
The 12z op GFS continues this trend; you see what is happening here that this huge surge of energy coming over-the-top the Ridge in western North America is forcing the PV --polar vortex -- to drop dangerously far to the south by D10. Again this is NOT a recent model development but a trend I have been seeing since Since 0z WED and even some hints before that. Take a look at the three maps below -- at 500 MB -- from the Midday Thursday 12z GFS and notice how the vortex is being dragged into Manitoba.
What this does is
1) bring in even More Arctic air to dominate most of the nation especially east of the Rockies... 2) establishes the mean trough over the Mississippi Valley.... which is WEST of where it is now.
Because you have the mean a trough position over the Mississippi Valley you must also have a downstream Ridge developing which in this case is over the Southeast and Middle Atlantic states. Thus any sort of Low pressure area which develops in the Delta is forced to take more of NE track as opposed to E or ENE.
This is exactly what happens here at 192 and 204 hrs on the midday Thursday Op GFS as well as many of the other medium-range models.
More significantly the European runs are very consistent over the few cycles... and closely matches the0z and 12z operational GFS . Day 6 and Day 7 --- again notice how the overall trough and Day 7 sharpens up dramatically http://www.meteo.psu.edu/~gadomski/ECMWF_12z/f144.gif
I have seen the operational European past Day 7 and the model develops a significant TRIPLE point Low area over the Tennessee Valley that moves ENE off the coast of VA or Northeast NC at day 8.5 or 9. I think that is a little too far to the south but it's the general idea in the overall sense.
The midday GFS ensembles are very supportive of the operational solution as well.... with many members showing a significant system tracking east Northeast off the VA or NC coast... some of the members have a more Northeast track.
The critical issue is going to be what shaped as the trough move into after Day 6? According to most of the medium-range models the broad U-shaped trough is going to change into a much sharper and elongated elliptical trough . If that happens then when Low pressure forms over the Delta it will be able to track further up the coast than the last several systems and there will be a significant snowstorm for much of the East Coast.
that being said to me also emphasize again that is a very fine line we are going to have to walk with the system along the East Coast. Take a look at the 12z Day 8-10 op Ecmwf and op GFS maps... they both show a huge amplified trough whopse center or axis is over or along the Mississippi vally.
Because we are not going to have a large cold HIGH to the North and we do NOT have a -NAO temperatures are going to be very critical and very sensitive along many of the I-95 cities in this event FEB 3.... ASSUMING of course it does develop. If we end up getting too much of Ridge over the Southeast the Low will track further north so iot will be more of a snow to ice to rain set up for the big cities of I-95.. On the other hand If we don't get enough of a Ridge the Low stay south and much of the snow and/or ice will fall across places such as TN NC and VA .
Lastly as a move in February the solution offered by the midday operational GFS at day 10 seems very reasonable to me and it is supproted by the 12z GFS ensembles