Real Weather Services Alert #4

Time 3;10 PM

Date: 1/26/2010

Potential exists for a significant snowfall from the PA/MD line south. All guidance as of 12 Z today has shifted this next area of low pressure further to the south. Even the most northern model which was the GFS has shifted to the south.

I have been reading alot about the reason for the shift to the south is due to the position of the Polar Vortex. This , however, is not the case. The Polar Vortex is actually to the east. The reason that this system is not being shown to come up the coast is due to a lack of phasing. If the two streams were to phase together then this storm could come up the coast. Is this a case of the southern stream energy being over poor data areas? This could be a possibility and we will know by 12 Z tomorrow if that is indeed the missing key to this winter storm puzzle.

Real weather services looks to the models for guidance but more importantly takes a blend of the models for the final solution. R.W.S also likes to look to the means when there is some question as to what to expect weather wise.

12 Z GFS ensemble means have shifted to the south and to the east. This is a abrupt change from its earlier runs of the 25th of January.

12 Z GGEM ensemble members 12 out of 20 show the low pressure area further to the north and quite a few even suggest a coastal hugger.

12 Z ECM ensemble means is about 30 miles further to the north and west and the precipitation is somewhat further north as well

12 Z UKMET has not updated on the source that i use so I have no information on that model. 

At this point and time the NAM does not go out far enough to cover the storm.

So where does this lead us? Here at R.W.S we are viewing the guidance as still not in complete harmony due to the factor that the ensemble means of two of the foreign models are further to the north and west and in one of those models much further north and west.  

R.W.S also recognizes that the southern stream energy is still not on land so the exact strength of this S/W is still not known. 

R.W.S feels that right now the best chances for a significant snowstorm are to the south of the PA/MD border. This would be using a blend of the models at this point and time. However..this is also not set in stone and probably will not be set in stone until 00z runs on thursday. 

R.W.S feels that since this storm is coming from the GOM that it is going to be heavily laden with QPF and its also possible that even though the low may stay suppressed to the south..with such a massive QPF shield that places N of the PA/MD border along the coast to slightly inland could end up seeing snow.

R.W.S does not think at this point that 40 N or PA/MD border north along the coast is out of the game..but chances of anything significant have been lowered at this point and time.

Stay tuned for further updates!