Real Weather Services Alert #5

Time: 1:30 AM

Date 1/27/2010

Dates Effected: 1/29-1/31

Real Weather Services continues to maintain the thinking that a significant snowfall is on the way for the MD/PA border and points south..

R.W.S also continues to maintain that until the energy gets on land we are still not at the final solution.

Summary of tonights 00z Model runs..It should be no surprise as to what we are seeing on the model runs tonight. As was noted earlier in the afternoon by R.W.S .. beyond 72 hours the models have had a bias of having the Polar Vortex to far south and too strong. We have seen on tonights models that the PV is continuing to move off to the east and the southern stream S/W is being held back over the Southwest longer.. What this does is it allows the PV to move out of the way and allow the energy coming down on the backside to attempt at partially phasing which then is causing this system to slowly become nudged northwards...

Tonights 00z ECM has jumped pretty solidly north with the QPF . 12 Z runs were bone dry in Richmond VA and had no precipitation to DC and tonights ECM has precipitation to DC and moderate precipitation in Richmond

To some this may seem insignificant but its actually quite significant. 

00Z GGEM also has come in more North and west then its 12 Z counterpart. Again, this should be no surprise as the ensemble mean was more N & W with the system and its QPF.

Here at R.W.S we like to point out potential red flags that can have an effect on a models outcome down the road. On tonights 00z UKMET at 72 hours the low pressure is over Central Lousianna..However its bigger brother the ECM is further to the south. This could be a potential red flag to the ECM that it should come further to the north then what it currently is being depicted.

00z GFS ensembles have also come further north with the QPF shield compared to the earlier model runs during the day on the 26th.

So..what does this all mean? This is the current thinking at R.W.S ..if the trends we seen starting at 18 Z on the NAM/GFS continue as they have in the 00z runs of the PV moving out faster and the southern stream S/W slowing down..this potentially could lead to a partial phase or a full phase (though much lesser chance) with the energy dropping in on the backside. This then would lead to an even more north solution.

As is now, a significant snowstorm is likely from the PA/MD border south but some  potential signs that are being shown are looking like precipitation could now make it north of that borderline, 

How far North is the question? If things continue to trend where they appear to be trending and that southern stream s/w is becoming stronger each run..and if that southern stream s/w coming on land adds extra strength..then we could be looking at this getting far enough north to effect NYC and extreme Southern New England.

Right now its becoming an almost certainty for south of the PA/MD border but chances of snow occurring North of that border have been upped slightly.

Stay tuned for further updates!