We have been talking about this time period for some time now. I actually think we were the first probably to start talking about this system and its potential based on the Heather A signal of the rising NAO from a negative state. We have been talking about the potential for a significant storm system along the east coast due to this signal in the teleconnections.
Some folks in the weather forecasting business have been saying things such as “Nothing supports a Major Storm” or perhaps “ or “consistency of a model does not matter”..
To those folks we would suggest researching Heather Archambault and study what she has found in reference to when the NAO is transitioning from negative to positive!
ITS ALSO BEEN NOTED BY HEATHER
ARCHAMBAULT THAT LARGE PRECIPITATION EVENTS OFTEN OCCUR DURING
PATTERN CHANGE
Perhaps this is something that they are not familiar with? Consistency in a model is also something that is very important. For example..You can not base a forecast on a model that at 00z calls for 1-2 feet of snow and at 12 Z now says an inch or less and then at 00z now says a wind driven rain storm. When forecasting the weather one has to take into consideration all the guidance available and then scour out those that do not make synoptic sense and are contrary to what teleconnections are in place and then to make that forecast take a blend of those models that do fit the bill. To do anything else is quite frankly WEATHER SUICIDE!
So with that out of the way lets look at the latest guidance..as of 12 Z and 18 Z.
First up is the UKMET. This model has been by far the most consistent model when it comes to showing a potent system effecting the east coast. It has been shifting east. However..it has not gone from showing a non event to an event or reverse. The consistency does not mean its correct ..however..the UKMET would definitely be representative of the type of event that Heather A talks about.
Nogaps at 12 Z..there is no doubt about the NOGAPS and what it is showing. 850s are plenty cold enough and it as well is showing a potent storm system (sub 992) moving up and along the coast. As of 18 Z this model has gone well OTS. Often this model will do that on off hour runs..so we will have to see what the 00z model does later this evening.
(not sure what happened to this image)
Now..the 12 Z ECM seems to be showing two sustems within the 72 hr to 120 hr time frame. However…with system number 1..the QPF is quite paltry and surface temperatures are marginal at best ..but it seems to focus more on the wave at 72 hrs out (wed) then the latter wave for friday /sat. At this present time it is the only model that is showing any measurable QPF with the wed/thurday event.
The next wave ..due to the first wave..deamplifies things and never pulls the baroclinic zone back in to allow the 2nd wave to effect the east coast.
Its ensemble means pretty much support the operational run but would argue for perhaps a more stronger system and west at 72 hrs . The means do show the second system from 96-120 hrs (the one the rest of the guidance focuses on) .
The problem with the operational ECM is its too much of a strung out system. Pretty weak area of low pressure not able to get organized due to what is mentioned above.
12 Z GGEM has the first wave going OTS or to the south and then OTS..
Second wave never really gets organized..generally because the trough is so broad and there are so many shortwaves within the flow that the model does not know what to focus on.
GFS @ 12 Z had two systems effect the region. Which is similar to what the ECM showed but the GFS was pretty cold overall and to the N & W of the major cities could argue for a wet snowfall. Then it had another system follow thru:
This followed up behind the previous low and was a fairly amped up system. Temperatures were fairly marginal.
Now the 18 Z GFS has changed its tune a little and no longer has two systems (like the 12 Z and the 12 Z ECM) but has one system.
This system forms over the southeast and essentially moves up the east coast along the coast. Pretty far west with its track but pretty well amped up and this causes the 850s and surface temperatures to remain pretty cold. Verbatim the 18 Z GFS delivers almost 1 inch of QPF to the ABE region which would support a wet snow event.
So there we have the break down of all the latest model guidance. The question still remains..will this be one system or will this be two systems within the time frame?
Well..if you believe the European Computer model there will be two systems ..one brings a shot of rain to the big cities on wed-thursday with snow further north possible and the other (operational) is a non event..
Majority of your people that are following the weather are essentially hugging the ECM and that comes right down to the pro mets with various agencies such as the NWS…some private pro mets as well.
Here at R.W.S we recognize there is no such thing as hugging a model.
We see no reason to change our thinking of a significant system moving up along the east coast. That significant system will more then likely be the friday/saturday time frame in which at that time depending on what sector you are in could mean a significant wet snow storm ( Far N and W of I-95) or if you are in the warm sector would imply flooding situation with some heavy rains. (along the immediate coast)
With striving for more accurate forecasts and it only being monday ..it would be foolish to start talking about amounts etc..However…chances are pretty good for a significant east coast system in this time frame.
Stay tuned for more information on this developing situation.
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