8:59 PM

If you put your ear to the ground, you could hear the fall of a million snow lovers faint to the ground after seeing the 12Z GFS, which basically if taken verbatum would produce a significant snowfall for most of the forecast area, save southern New Jersey (even that location would still get measureable snow if the 12Z guidance is correct).  However, before we get ready for an all snow event, we better reason a bit on what the GFS and other guidance is suggesting.  Let’s deal with the 12Z GFS right off the bat.

12Z GFS:  The basic idea of the GFS is this.  The strong shortwave, which is a closed 500 MB low over the central Great Lakes by Friday morning runs into one very impressive 50/50 low at 500 MB.  Sensing that there is no way that the disturbance can go much further east, the strong PVA dives towards the Mid Atlantic coast.  The short wave trough tilts to the negative towards the coast and a coastal low is spawned.  The cold air on the model is kept over the coastal plain as the developing coastal low bombs outs and pulls the deeper cold air towards the center of the low pressure system.  Heights crash.  Intense lifting is seen along the coastal plain, and everyone gets into the snow parade over the forecast area along the coast.  The position of the high pressure is mute in this scenario as the idea is the cold air behind the clipper reenforces and strengthens the marginal cold air in place left by the previous clipper on New Years Eve.  So can this solution happen? 

Verbatum, I think that the idea of no mixing of sleet and/or rain along the coast is a bit of wishful thinking especially with a high pressure system off the coast.  The strongest high over eastern North America is over Ontario, but too far away to have a direct impact on the forecast area at this point.  The key here is that the coastal low boms and tracks in such a way that cold air has no where else to go but towards the coastal plain, and any warm air advection is forced above 700 MB to not produce significant change in precipitation type.  Although even in this situation, you have to expect some sleet.  So by the naked eye, yes the solution looks like a significant snow storm for the forecast area.  However, reasoning of the set up should lead up to the idea of some mixing back and forth through the evolution of the storm.

As for precipitation amount, the 12Z GFS produces intense Omega at 850 MB as a new 850 MB low quickly develops and significant low level forcing develops as a result of the bombing low pressure system.  The guidance suggest a deepening rate of around 2 MB per hour between 18Z Friday and 06Z Saturday.

The 500 MB set up is possible.  Yes.  There is also support of this solution with the Ensemble guidance and the UKMET.  The NAM hints at the possiblity as well.

12Z ECMWF:

Then we have the ECMWF, which likely caused snow lovers to faint again.  The ECMWF and the 18Z GFS for that matter completely loses the storm.  Why?  Well, because of the other possible solution.  The ECMWF and GFS up to 96 hours or Friday morning is rather similar in the upper level set up.  A strong 50/50 is in place.  A strong disturbance is driving towards the Great Lakes.  Then BAM.  The ECMWF loses the storm.  Where did it go?  The answer is that the ECMWF decides to try to merge the disturbance with the 50/50 low.  Basically shearing the storm appart and not allowing any sort of redevelopment.  Why would the low need to redevelop if the low simply falls apart?  Well, I have some problems with this idea.  First, I could understand if the disturbance was weak and unorganized, but this disturbance is anything but.  Although the blocking is strong, I doubt that the entire upper level system will just fall apart and those lead to a non-issue of a storm for not only the forecast area but the entire Northeast.  The idea just sounds suspect to me.  So for now I am throwing the solution out.  However, if the ECMWF is trying to pick up on the idea that this disturbance is much weaker than what has been forecasted, then the idea of this storm being sheared apart is plausable. 

00Z Guidance:

The 00Z guidance is going to be very interesting to watch tonight.  Why?  Because the models will be getting a better read on the disturbance, which is currently over the coastal waters of British Columbia, really is.  If the disturbance is as strong as what has been advertised, then I think we end up seeing guidance similar to the 12Z GFS.  If this disturbance is a 98 lb weakling, then the 50/50 low will crush this disturbance like a tin can, thus leading to a non-event for the forecast area. 

From this point on, we will get a much better feel on not only the evolution of this storm, but the track and some boundary layer characteristics. 

So the next few days are going to be hectic for all of us, but hey we have the summer to rest!