As we have been talking about for several days now winter is about to return and those that were spoiled by the warmer weather and thinking winter was over are probably going to be in for a rude awakening. Temperatures today were dropping all day and were being ushered in with some very strong NW winds. Winds have been gusting into the 40s and 50s thru out the region which has been ushering in colder air. This colder air is going to set the stage for potential winter weather Sunday Night into Monday night and perhaps another round of winter weather on Tuesday…
Latest guidance as of 12 Z has actually started to trend further to the south with wave #1 and then for wave #2 the guidance is still split. We feel the reason that guidance is starting to trend south with wave #1 is because it was too far north to begin with. If you are going to have confluence strong enough to make the second wave south..then it only makes sense that with the storm being 6 hrs apart that the first storm would not be as far north.
As you can see by looking at the guidance above for wave # 1 ..the ECM is actually the model that is further to the south then the rest of the guidance..however..all of these models have trended further to the south with this first wave. Presently we think that the ECM probably has the best handle of the track with wave # 1 but we believe that it is probably too warm at this time range. This can be a bias of the ECM model and usually by about 24 hours out the model will actually be closer to reality with the temperatures.
We have been talking about how it will depend on where the polar boundary sets up and this is the track that the systems should ultimately travel across. Right now we feel that boundary will probably set up just along or just south of the PA/MD border and that is pretty much what we have felt from the start of tracking these systems.
Now..as of 18 Z ..the NAM actually moved further to the North with wave #1..while the GFS actually moved further to the south from 12 Z..
Compare that to 48 hrs and you will see that it has come south. Now..you may be reading across the internet that this can be attributed to the models southeast bias at 18 Z runs. First..there is no truth to this statement. 18 Z runs are as valid as any other runs of the GFS. Second as we see above the ECM was further south then the GFS at 12 Z…and with the ECM in the short range being a better performing model it makes sense that the latest GFS has come further to the south.
The 18 Z GFS actually brings with wave # 1 about .50-.75 from E central PA and points to the North. Surface temps are below freezing in the same areas and 850s are as well so if this were to be pure snow those areas above would be looking at about 5-7 inches of snow. However..there could be some warm layer in there so ..the scenario would look like snow and some sleet/zr possible with wave #1 . To the south of those areas however..temperatures would be warm enough for rain or a wintery mix.
So at this point and time it appears that wave #1 will bring the areas from about central PA and north the best chances for some snow along with some ice potential.
This brings us to wave # 2. Models for the most part have been suppressed with wave # 2. Now there is some model divergence on this so..we will once again look at the guidance from 12 Z with wave #2 .
The NAM shears the system out and has it pretty well to the south with perhaps a light snowfall in Southern PA and then heavier amounts south of the PA/MD border..
GFS paints a similar picture as the NAM with wave # 2.
Now lets look at the foreign models..
GGEM shows a stronger system with QPF more to the north then the american models above. Nothing impressive but a light snowfall for central PA and points to the south in PA.
ECM we see no surface reflection of the low however…compared to the two prior runs of the ECM..the QPF from the system is further to the north. As prior runs the furthest N was ABE for light QPF..now the furthest N is in NE PA. So while the American models are south ..the ECM is slightly further to the North and more similar to the GGEM.
Perhaps the most interesting foreign model of them all however is the UKMET..
UKMET has a stronger system and would be a decent snowstorm across the region. This could potentially serve as a red flag to the ECM with its not strong enough nor far enough to the North.
So the foreign models actually give a fairly strong reason to continue to monitor storm or wave # 2. As well as the GFS means from 18 Z..
Presently it would appear as the second system would take a further south track and bring some lighter snows into SE PA , S NJ and DE and MD..
However..with the foreign models indicating further north and the track of the first wave coming further south (towards the PA/MD border) ..this second storm will likely depend on the boundary from the first storm and where it sets up.
Edited to add:
There is some more mis information going around on the internet. That is that once one gets inside 72 hours they should stop looking at the GFS means and start looking at the SREFS (NAMS ensembles) ..This simply is NOT TRUE! The SREF is the NAMS ensembles and the NAM was not created to be used beyond 48 hrs. So if we are talking about a system beyond 48 hrs..you would look at the GFS means before the SREF.. Under 48 hrs then you would look at both the SREF and the GFS means. So..please be careful with some of the information going across the internet!
Stay tuned for further updates.
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