Alright there still seems to be alot of confusion going around the internet and this is because of two American Models. Now..before we get to looking at the guidance..the very first thing I want to do is to look at the pattern.
MJO or Madden Julian Oscillation is currently in phase 7 and looks to be headed towards Phase 8. By the time of this storm which is still 72-96 hrs away we will probably be borderline 7/8. These phases, especially phase 8 are very favorable for east coast winter storms.
The arctic Oscillation is actually negative but expected to rise towards neutral in the next 7 days. So with a negative AO we do have a supply of cold air available to tap into.
NAO is negative and expected to go towards neutral negative over the next 7 days. This is a change from before which was more a neutral positive. So this too would be more supportive of colder air available.
Next is the Pacific North America Oscillation or the PNA. Clearly the PNA is positive & a positive PNA argues for a trough across the east and a ridge across the west. So as you can see all teleconnections are favorable for an east coast storm.
Now lets look at the guidance and we are going to start with the 12 Z Nogaps followed by the 18 Z Nogaps..
Keep in mind the SE bias of this model and notice where it ends up at 12 Z at 96 hrs.
Notice how a model with a very progressive SE bias is very close to the coast? With the models bias this should be more south and east.
So lets see what the models have done at 12 Z & 18 Z.
Well as you can see the GFS is still taking this system off the coast and out over the gulf stream. This is the models first error. The system is going to want to develop and track along the greatest thermal gradient which is on the western side of the gulf stream. Secondly we can see that the GFS at 12 Z is no more closer to the coast then the NOGAPS. So this is certainly a flag to the GFS/and its ensemble means. What about 18z?
As you can see it stays on its same track and if you now compare it to 18 Z Nogaps it is well out there beyond the Nogaps. So again we will consider this model as an outlier at this point and time.
GGEM..its kind of funny when one looks at the GGEM because it is actually showing what the Nogaps was showing at its most western extreme model run. The GGEM essentially goes across C Pa. This was what the NOGAPS had done as well at one point and time. The GGEM is too far west & while a track that west could happen..the chances of it happening are slim less then 2 %. The GGEM would be rain for alot of folks and alot of it. Exception being western PA and NY.
Now people are bringing up the GGEM ensembles and how they are further to the east. This is indeed true but with what was just said above you would think the means would be further east. However, at the same time what these people fail to mention is that the means are trending west. Of course you will hear that the western members of the means are skewing the means. That is only true if you do not know that the means are a smoothed down average of all the solutions & in order to get a means further to the west..it means more members are west then there are east members.
00z GGEM means
12 Z means
One can clearly once again see that the 12 Z indeed is more west then the 00z.
Many have claimed the UKMET is out to sea. This simply is once again misinformation as at 84 hrs the UKMET is actually snug to the coast of Hatteras. From there it moves ENE and ends up in a position about where the GFS is at 96 hrs. Once again using the NOGAPS bias and how its more west..one would expect the UKMET to come back west as we get closer to the event.
All that remains to discuss is the 12 Z ECM…
Now as you can see above the ECM has actually trended more west with the area of low pressure & this is very evident when you look at the QPF image. I am not going to do the normal breakdown of the hours like I normally would do ..but basically from East Central PA to NW NJ and 40 miles Inland from the coast to the NE would be cold enough to support all snow. To the West of KPHL in PA and then in MD from about WC MD on all are cold enough to support snow. The temperatures are in the lower to mid 30s at the surface with the exception of Central Jersey and South they are 35-40 and then along the coast into SNE they are 35-40. Basically if you are inland..you are looking good for a heavy wet snowfall.
The means are above and as you can see the means are pretty much more organized and amped up ..There are about 30% of the members that are more west then the op.
Current thinking has not changed from what we have set out with from the beginning of tracking this event. If you are N & W of the cities you will be a snow to wintery mix..far N & W mainly a heavy wet snow. In the cities themselves more rain then anything else with the potential of some snowfall at the start and at the end.
Track of the storm would be along the eastern side of the appalachians (inland ) to just west of Hatteras and then NNE from there within 50 miles or less from the coast.
We are upgrading to a level 3 alert for the interior regions from Md on NE . Potential in the interior regions exists for a significant winter storm with a heavy wet snow accumulation.
As you can see the ECM QPF outlook below…
(removed cause accuweather complained)
One thing to consider is the airmass that is in place before this storm arrives is extremely cold. This cold air at the surface will be very hard to dislodge and could be stubborn to leave the area in the areas where rain is expected. So this could result in ZR. This is something we will have to keep an eye on.
Stay tuned for more information on this winter storm!
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