Posted by wxrisk | GENERAL,WINTER 2012 -13 | Thursday 13 December 2012 12:18 am

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.



  1. Pingback by East Coast winter storm Dec 18-19. « coastlinesproject — December 14, 2012 @ 2:16 pm

    [...] DEC 18-19 EAST COAST WINTER STORM… Posted by wxrisk | general,winter 2012 -13 | Thursday 13 December 2012 12:18 am [...]

  2. Comment by beams — December 22, 2012 @ 3:21 am

    i guess this site is done. really liked this guy anybody got any other site to go to

  3. Comment by Weatherbane — January 2, 2013 @ 6:14 pm

    This was great stuff. I’d like more updates please.

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