1845 HOURS EST 12 DECEMBER 2012… STARDATE 201212.12
I think now is a good time to review where things stand with regard to the overall pattern … and specifically with regard to the December 17 LOW… and the December 18-19 Low (which clearly is going to be the bigger of the two events).
First let me make a clear statement about where the forecast is headed and about my thought process. My ORIGINAL thought process from earlier in the week was that the MAIN Low was going to track up through the Ohio Valley then “jump” across the Middle Atlantic states and reform off the New England coast (called coastal redevelopment in the weather biz). And while I was forecasting or a least anticipating the possibility of heavy snow for central and northern New England ( 12″+) … I also asserted that the Main Low … which in the weather business is refer to as the “PRIMARY LOW” … would bring heavy snow to portions of the Midwest and the Great Lakes. That is no longer going to be the case and in that respect my preliminary forecast/ speculation is going to turn out to be WRONG. I don’t have to wait to December 18 to figure this out. Wrong is wrong and and with respect to that part of my preliminary forecast .. I am going to be WRONG.
There are two specific reasons why my initial assessment have turned out to be wrong. FIRST … I was skeptical about the models are building the block pattern ( West based -NAO) into Eastern Canada and Hudson’s bay before December 20. Given the fact that the models and over forecasted this event price before I think by skepticism was well warranted. SECOND… this image shows the Pacific jet. It’s very strong and very powerful and shows no signs of rapid weakening. What this means is that systems coming in from the West Coast are being driven across the country and are being forced consistently eastward. So originally when it looked like the main Low pressure area was going to track into the Midwest … the strong Pacific jet has kept pushing the DEC 18-19 Low further east …and …east and …east and now in ends up on the East Coast
On the other hand with respect to the the argument / forecast that most of the precipitation over the big cities of I – 95 is going to fall as rain …. is looking more more likely. My analysis a least so far according to most of the model data has been correct . The Upper air features which are needed to support a East Coast snowstorm are not there. There is not nearly enough low level cold air over the coastal Plain and there is no col air source.
In addition I have also seen a lot of speculation from some weather hobbyists and a few meteorologist –who should know better –that this event for DEC 18-19 has a lot of of similarity to the great Middle Atlantic s snowstorm of December 19 – 20, 2009. That analysis is delusional. It’s like saying …..”World War 1 had tanks and planes so in that regard it was just like WWII…”
Let me explain why the two events not similar. This image shows a comparison of the upper air mapS between the two events. The map of the LEFT HAND side is the Jet stream ( 500 mb) map from 18 DEC 2009… and the map on the RIGHT side is the pper air map from this Wednesday morning European model Valid for December 18, 2012. As you can see there a number of key features which are not even close to being the same.
*The blocking pattern is vastly different.
*There is no West Coast Ridge to speak of with this upcoming event but back in Mid DEC 2009 there was a major ridge on the West Coast.
***And finally the air mass over the Eastern US on the two days BEFORE on the 19th of December 2009 snowstorm was much much colder than what we are going to see next week.
DEC 16-17. This event is being somewhat overlooked –as it should be since it is the weaker of the two events — but for folks in interior New England and central and Northern New York State this Low could drop several inches of snow. The map on the left hand side is the operational or regular European model hand the image on the right hand side is the European ensemble. If there was enough time between this week are low and the bigger event on December 18…. Then we get more cold air into the northeast U.S. and stand a better chance for saying snow. But that is not going to be the case.
DEC 18-19 LOW
This image is the midday Wednesday run of the GFS and you can see how the model has moved to track a below inland . If we assume that the GFS is correct then everybody over the coastal plain even into Boston would see primarily rain…. And although snow would be over the mountains of eastern and Northern West Virginia Western Maryland western and Central Pennsylvania western central and Northern New York State and central and Northern New England.
This next image is from the European model from the 12 Z or midday Wednesday run. The image on the right hand side is the 12z operational or regular European … The image on the LEFT side is the European ENSEMBLE. Clearly the operational regular European is a driving rainstorm as the actual deepening Low pressure area is located over southeastern Virginia. Winds are very strong along the coast probably gusting up over 50 mph. What is interesting here is that the European ENSEMBLE is a little further to the east and it is colder and implies a lot more snow for the Piedmont areas of the middle Atlantic states that is to say the area between the coast and the mountains… This would include areas such as northwest Virginia …Central Maryland …eastern and southeastern Pennsylvania (such areas as reading Lancaster and Allentown) just north of New York City in places like White Plains ….Central Connecticut and even into Boston.
If the European ensemble turns out to be correct…IF… IF…. the it is quite possible that the rain will END as snow the big cities the Northeast and areas just inland from the big cities of Washington Baltimore Philadelphia New York could see several hours of moderate or heavy snow with some accumulations. The site may also occur over the northwest third of Virginia.
Once we get beyond the system the overwhelming amount of data clearly shows that the big coastal storm will move up into southeastern Canada and become connected with the blocking feature over Hudson’s bay and Quebec Canada. The interaction of these two features will allow for true arctic air and strong north wins to cover all of the U.S. east the Mississippi River DEC 20-25.
Finally beyond this event there is the potential event for something in around Christmas day. Whether not the weather models pick up on this event is questionable. Essentially what I am thinking about is that all the energy coming in from the eastern Pacific into the West Coast is going to Eject a small piece of energy across the southern Rockies and into the lower Plains sometime before Christmas. If this energy is strong enough … IF… THEN given the the overall pattern with the massive Block over central and Eastern Canada…. should drive this feature East … NOT northeast… and it could be a band of snow across places such as TN NC VA maybe soihern KY and MD/ DE.
This is the jet stream map at 240 hrs from the operational GFS and it shows some sort of weak piece of energy busting through the southern Rockies into the lower Plains on DEC 23.
The GFS ESNEMBLE mean shows this energy over the sw states coming out later… DEC 24 which is whatbthe euro ensemble at 312 – 336 hours shows. This would delay any event until DEC 26.