I wanted to post my thoughts before my cold medicine knocks me out for the rest of the night.  

I’m sure everyone is excited by what was seen on the GFS today, especially the 18 Z guidance, which supported the 12Z run.  So why did the GFS go so cold?  Simple, remember that clipper that I was discussing this morning?  The one that I found intriguing.  Well, the GFS takes a very different take on the interaction of the southern stream disturbance and the clipper low.  First, the important key here is we are seeing a trend from ALL model guidance of slowing the southern stream disturbance down.  This is due to the intensification of the southern branch disturbance into a closed low.  The large majority of the guidance including some of the SREF guidance is now depicting this scenario.  As a result, the cold air has more time to build into the forecast area.  Additionally the slowly of the upper low over the Southeast allows for the clipper over the Great Lakes to interact with the coastal storm, and BAM, colder solution.  Now, am I ready to jump all over this solution?  

Not yet.

The problem here once again is that we don’t have a slam dunk case for the southern branch disturbance to slow down.  Sure, the ridge over the Atlantic would prevent the disturbance to exit to the East, but not necessarily slow down the storm.  That’s one of the key impacts of a negative NAO, which is not present.  So I would say that right now there is a strong case for heavy FROZEN precipitation for the coastal plain, but certainly not a slam dunk.  I want to see the 00Z guidance continue the trend of this interaction before I issue an official snowfall/ice accumulation map.  

Also note that the ECMWF depicts an equally rational case for a mostly rain event for the coastal  plain as the clipper remains separate from the coastal storm, thus a warmer solution.  So obviously, there is a lot to consider over the next 24 to 48 hours.  A wise forecaster would not jump the gun just yet and wait for more guidance, and that’s exactly what I’m doing.  That, and hoping I feel less stuffy by morning!