1145  EST   15 JAN

The   FIRST  issue   we have to deal wth is  in the short term and wave of Low pressure which is going to develop on the cold front on the 17th and 18th as it moves through the Midwest and towards the East coast.  Although this is going to be primarily a rain event for the  Ohio valley  and all of the Deep South…  from Virginia and northward into the big cities of I 95 –there  is  some uncertainty as to the precipitation type and how long frozen precipitation is going to last before changes over    to rain.

All the models agree   that at 60 hours  — the afternoon of the 17th –there going to be two areas of Low pressure over the middle portion of the country.  One will be  the   Great Lakes and the other over the Delta.  Originally it looked like the southern Low was going to track  up the Appalachians  or just west of it ….which would ensure that most of the precipitation  (even into southeastern New England )   would fall as rain or snow rapidly changing over to rain.  However the new model data is showing the southern Low developing a bit stronger and tracking much further to the east.    The  Oz  GFS  the 6z GFS and the 0z   EURO a fairly strongly with the coastal low taking over by the inning of the 18th .

Complicating this even further it is the arrival the fresh cold area of High pressure on Sunday and Monday across the Great Lakes and into New England.  If the  cold HIGH was to stay locked in over the Northeast ….then this event could be a lot more snow and sleet then rain for anybody from Virginia to Maine but that is not going to happen.

There is no blocking feature in the jet stream over Eastern Canada and / or Greenland and there  is no  Low  either at the surface or in the upper levels over southeastern Canada.  This means that the cold High   IS going to slide off the New  England coast  so winds will NOT  stay NE  but  turn  to a  East  direction.    This in turn  means the cold air   over the  coastal  Plains of the  NE will get  eaten away.

   For the Great lakes and the northern portions of the Ohio Valley   and for the interior portions of the Northeast …such as   western and central PA and NY this will be primarily a snow going over to sleet event and significant accumulations are likely . 

However  for the NE  quadrant of the nation — Maine to   Virginia –the key is going to be the timing and arrival of the precipitation over the Northeast.  IF the precipitation begins early enough that it will start as snow or sleet over  western  VA    and MD.  It  MIGHT  begin as frozen precipitation over   central and eastern VA and   eastern  MD but it should quickly change over to rain there.   But  over  WVA   western  1/3 of  VA    western  third of MD  significant snow  & ice   is a  real possibility especially if the  Cold High    manges to  keep the  WEDGE of cold air  in place   over the    VA Piedmont.  

For the big cities of I95  –  DCA  to   BOS…  There is little doubt that the southern portion of the big cities   –  DCA  BWI  PHl  cities will change over to  sleet then rain.   However  over   NYC   CT and BOS more than half of the total precipitation may be either snow or sleet  with additional accumulations possible and the precipitation and being as rain .
Down the road the pattern shows more promise if you like cold weather and winter precipitation.  So far this winter  three  have been distinct blocking intervals  or  episodes in the atmosphere over the western hemisphere.    The Blocking has been the development of a bubble or block over Greenland which has retrograded — moved west and set of east– into Eastern Canada and then eventually into North Central Canada and then into Alaska. 

It is the   repeating     re-development of this block   which has caused the pattern to become  cold and stormy.   In the last two episodes of the blocking we saw two very distinct major East coast winter storms which  occurred as the blocking episodes were weakening or falling apart.  The first coastal storm was the December 25 – 26 nor’easter…  which is coming at the end of the very strong  2  week blocking episode which is falling apart over North Central Canada.    The second event was the January  10-12 coastal storm which was a major event from Alabama to Boston  — except for Central  and western Virginia  — which also a occurred as a intense blocking episode over Eastern Canada was coming to an end.

After the January 18 event the models all show a strong cold front which is going to drive deep into the Plains and into the Deep South.  The European model on Friday the January  14 develop significant low pressure on the front….  as  cold HIGH pressure  moved into Montreal and Vermont.  You can see what the model was showing here. 

  If the European model is correct it would be a major winter storm….  bringing possibly significant ice into Northern Georgia   northwest  SC    much of NC  and   snow  over  much  of  VA into  MD  southern WVA  DE and possibly into southern  PA and  southern NJ.   The 0z   SATURDAY   EURO    continues to show this event  for JAN   21-22.

  
0Z  EURO   ensembles

 The  12z GFS and GFS  ensemble from yesterday did not support this solution at all .  Those Models    show   just large cold arctic High dominating the weather east of the Rockies and especially Eastern Mississippi River.     And the 0z  SATURDAY and  6z GFS continue to show no such event of any kind around January   21-22.   Not surprisingly the  0z European and European   ensembles  continue to show a significant event .

Because this is a southern stream feature –that is to say the Low pressure area is a piece of energy in the southern jet stream which will be coming out of the Gulf coast or Delta region –  it is likely that the GFS  Models which do not handle southern features well at all ….will continue to not see the system until about 72 HRS before the event . 

Instead the 0z   GFS  has a major coastal event developing around January 25.  The model does this because it takes the blocking which develops east  of Greenland and pulls it back towards Greenland and then Northeast Canada.

Longer term the European model yesterday showed a the return of a massive blocking feature over Greenland.  This   would be in the fourth major episode of strong   Blocking   over Greenland   ( called  a -NAO  Iin the weather  biz)   and it’s not even February 1 yet.

The data this morning however is not quite as impressive with this potential blocking feature.  The European model shows the the strong block developing but has it east of Greenland closer towards  Iceland….  and this is supported by the  GFS and GFS ensemble.  

When   the blocking develops east of Grenland  — is called   EAST BASED  – NAO.   When the blocking is over Greenland or northeastern Canada it  is  referred to   in the  weather    biz as a   WEST BASED  -NAO.      Got it?

If you like big East coast snowstorms then  you  want  a  good strong   -NAO   feature to help set up the overall winter pattern in the jet stream.  However there is a difference as to the favorability of a  EAST BASED -NAO  vs  WEST BASED -NAO.    The western -NAO there is the entire East coast   (see DEC  25-26  and JAN   11-12)     whereas as a   eastern based -NAO   favors  NYC  to BOS.

At this Point I believe that even if we do end up seeing a  east  BASED   -NAO  initially did well retrograted back in court Greenland and northeastern Canada before the end of the month which will set up another stormy episode for the eastern third of the  Conus.