As everyone is quite well aware the models had given up on the ideal of a White Christmas because they were ejecting the energy from the cut off low over the SW too soon and the storm has become delayed now till the time frame of the 28th-29th. Post x mas storm!
However, before we look at the guidance we are going to take a look at the teleconnections that are in place..
First up is the Madden Julian Oscillation and you can see as of the 23rd we were in Phase 5 of the MJO. Phase 5 is a warm phase for the eastern USA and much of the USA in general as the below image will show you..
These are your 500 mb anomalies and as you can see blue is no where to be seen in the USA but rather green which indicates a warmer then normal pattern.
This should come as no surprise as we see that both the GFS and the ECM are both showing a very positive Arctic Oscillation
Whenever you have a positive AO it means all the cold air is locked up to the north and the USA is generally above normal and this has been the case since at least November 1st..
The next is the North Atlantic Oscillation and you can also see that we are looking at a very positive NAO which is forecasted to go negative but not in time for this upcoming storm system. When the NAO is positive it is very hard for storm systems to slip off the coast to the South and east and inland runners become more common.
Finally the PNA is neutral at best right now but as you can see it is expected to rise. When we have a positive PNA this correlates to troughing in the east or central part of North America and a ridge to the west.
So what we are looking at is a + AO +NAO neutral PNA and a very positive EPO. Along with the MJO in an unfavorable phase.
So the reality of the scenario is that we are having warm signals and it should be no surprise when we see the CPC issue this type of map for the 6-10 day time frame..
Now, that is a pretty clear picture of what the teleconnections in place indicate. This would be the over all theme but it does not mean that some cold air intrusion can not happen it just will not be sustained and that leads us to the storm system for the 29th and 30th.
With a rising PNA this would indicate a trough digging into the east. However..with the other teleconnections unfavorable for any real “arctic air” we are looking at some colder air or more seasonable air incoming . The question is whether or not this colder air can make inroads before the storm system comes out of the Southwest.
The other piece of the puzzle is all season long we have had a SE ridge in place and the models have been generally under doing this ridge in the medium and the long range. Matter of fact if you believed the GFS about two weeks ago we should be in a very cold pattern right now and for the next couple weeks. They been under doing the SE ridge and trying to rush in the pattern change..
Now lets look at the guidance for the upcoming storm..
Now as you can see the ridge is pumping out ahead of the system and this system becomes an inland runner. Matter of fact it travels thru central PA into Central NY.. Below is the ECM verbatim off the accu pro images:
At 72 hrs. the 540 line runs essentially right at KPIT in a north to south fashion then bends towards the NE along the US/Canadian border..Temps at 72 are as follows: 30-35 from about central PA west Into the NE.. from north of ABE SW into SC PA 40-50 degrees and these go into New Jersey and SNE ..At 78 hrs. low pressure is over SC NY almost on the PA/NY border..540 line is into East Central PA.. then the 540 line runs NORTH to touching the eastern side of Lake Ontario so the only part of NY that is behind the 540 line is the part that is SW of Lake Ontario it then runs right along the Canada US border so all of NEW ENGLAND or the NE is on the warm sector side...temps are now 35-50 depending where you are Located from NE PA SW into South Central PA ..North central PA (SC PA and NC PA are 35-40) so the temps rise from 72 hours in these regions..these 35-50 temps then go into the NE into SE NY/Central New England and into Southern Maine where they are in the 40 degree range! At 84 hrs. the 540 line has now crashed thru all but VT/NH and NE into Maine which is still warm sectored and the low is over VT/NH temps at this hour are now 30-45 across the region with the warmest NE of the center of low pressure! 1 inch to as much as 2.5 liquid total equiv...
Now as you can see the ECM verbatim would be too warm for much of the area to see any snowfall with the exception of western PA and parts of Western NY..
The image above is the 00z UKMET along with the 00z ECM and you can see that the two models are in pretty good agreement with the track of the low at 72 hours and the UKMET also is a warm model run for this system.
GGEM not quite as far west as the UK/ECM but again you can see that it is showing an inland runner and also the 540 line is pretty far to the west.
Then we have the GFS..
Now as you can see the GFS is SE of all the other guidance and it is also slower then the rest of the guidance. You also notice that the cold air is a touch stronger on the GFS but when you look at the surface temps you see that they are the warmest underneath the heaviest precipitation where the 850s are above 0 and so is the surface..
This would indicate rain along the east coast with some lighter snows in the lighter precipitation to the west of the blue 850 line.
However we also see that the GFS is an outlier when it comes to the rest of the guidance.
So we have essentially four models that are showing far western areas with the potential for snowfall , and these areas may start as rain..and for the rest of the region they are indicating heavy rain.
With the teleconnections that are in place we feel that the best chances of snow are going to be in the areas to the west. This would be west central PA into western NY and into Western New England.
This would be taking a blend of the 00z UKMET/ECM/GGEM and about 10 % of the GFS since it appears to be to SE which would make it to cold at the surface in some locations.
The teleconnections in place would point more to a coastal hugger or an inland runner.
It is way to early to speculate about accumulations. This would not be a 10:1 ratio for places that do get snow because the 850s are not all that cold in locations that will be cold enough to change to snow.
So this is our current thinking at this point and time..
If we were to take the ECM verbatim the rain line would be further west. The GGEM would also be further west. And the UKMET would also be further west but the above is a “blend” of those three models.
Its also important that people realize when we analyze a model it is verbatim to what the model run is showing but does NOT mean that that is what we are thinking. The ECM would suggest ALL RAIN for pretty much all of New England and you can see that we do not have ALL of New England in rain! The GGEM would be pretty much the same story as well as the UKMET. And this STILL could end up being to cold above..
If the ECM track verbatim ends up being correct along with the UKMET then the snow area will decrease but for NOW we are using a blend..
Stay tuned …
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