The time period we are talking about is the weekend. Friday into Saturday ..or perhaps late thursday night into friday night..
Generally this season models have been having a really difficult time with forecasting storms in the medium range or around 72 hours out which this is approx. As of 00z guidance tonight we have everything from thunderstorms with heavy rain potential to a snowstorm potential for those N & W of the major cities.
We have two major models that have been relatively consistent. The GFS/ECM but they have two totally different solutions.
You can see that the GFS is the model that would support a snowstorm for inland locations from about E Central PA and points to the west and north..
On the opposite side of the spectrum is the ECM which at 66 hrs (sorry its a pay site image) is over SW PA…quite the difference for 72 and under…
Looking at the rest of the guidance ..
UKMET which is not available at 66 hrs is shown here at 60 hours and this would be considered an extreme western outlier.
GGEM at 66 hrs is over SE PA essentially which is closer to the GFS operational track…then it would be to the ECM operational track..However..its snows would be further inland then the GFS.
The NAM at 66 hrs at 00z is also on the eastern side of the solutions but also the snows would be further inland then what the GFS shows.
So we have the GGEM/NAM similar to the GFS but warmer and or further NE…
UKMET extreme western outlier..
ECM further to the west & warmer and also supportive of a thunder with rain event.
So we essentially have no model agreement and we are about 72 hrs out.
Normally the GFS would be considered an outlier with its colder solution..however..it has support from its ensemble means and more importantly only 3 out of 12 members are further west then the GFS op. This means that 9 members out of 12 support the OP and you would not expect this model to change all that much run to run..
As far as ensemble means the 00z GFS means and the 00z GGEM means essentially agree on the 60 hr position and 72 hour position but there is no access to the in between hours.
You can see some fair agreement there between the two different means. This leads us to believe that the GGEM individual members probably closely resemble the GFS individual members as well.
So what causes the differences between for example the ECM /GFS? I believe the differences start at 48 hrs already..
You can see at 48 hrs already the GFS digs the energy further to the south and is also weaker with the system at that point and time. Now..what is interesting is that both the models show a strong negative EPO around this time period.
As you can see by the images above. What this means is that you will have a strong southeast ridge in place. They also both show a rising NAO from neutral negative and a negative PNA..
Generally speaking ..the NAO rising from neutral negative to positive is a signal for a big east coast storm. Throw in the wild card on top of this of the MJO..
Which is in phase 7 and you have some more support for a GFS like solution as phases 7,8 and or 1 are the best for East Coast storms. The negative EPO also would be sending ridging out west which would cause this energy to dig further south as indicated by the GFS..
However..at the same time we can not simply just side with the GFS model even though it does indeed seem to have more support..fit the teleconnections better.
At this point and time we generally think that this should take a track from NC Arkansas to Northern West Virginia.
The question then becomes does this continue to move NE from that point or does the confluence from the high pressure dropping into the Central states cause this to take a more easterly track?
We are going to be honest and say that right now with guidance not in harmony it is just to early to know the complete answer at this time. The best bet scenario seems to be that the big cities would be rain..perhaps ending as snow and the inland locations (how far inland is not known yet) would be a wintery mix to snow scenario.
We are keeping in the back of our mind the past two systems which just delivered snow across the region ..and how at this time range they were modeled to far to the north and west..too warm and as rain..and the final result was snow!
So stay tuned for more information on this developing winter storm.
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