1515  EST   19 JAN
This whole event for the weekend is turning out vastly different from what I thought was going to happen over the past weekend–  that is to  say JAN  15-16.  Recall or read read the post below from a afternoon of the 16th the the scenario which I was considering was that the cold front which sweeps through the east coast first…. on JAN 20… then  when the front stalled a second piece of energy would interact along the front …  and develop a second larger coastal Low   for  at least some portion of the Middle Atlantic Coast and possibly into New England JAN 22-23.

Since that posting   obviously a whole lot of data has come out and this scenario is no longer viable.  The first change has to do with the cold front.  It still going to come through on the 20th  or 21st but the the Low pressure area is going to develop on the cold front BEFORE or just as   the front is  reaching the the Middle Atlantic states.  This greatly reduces the  chance  if seeing ANY accumulating snow over Central  … southwest   and    eastern Virginia.

Another  reason is that ahead of the cold front we  have  a pretty mild air mass.  Temperatures have surged into the 50s  across the Middle Atlantic states   this afternoon…  (which oddly enough  is exactly what I  have been forecasting from last week to my private clients even though the  GFS  MOS  guidance only supported temperatures in the lower to Midddle  40s.)  With SW winds coming in a head of the cold front tomorrow and mild temperatures currently in place any precipitation is going to fall over Central Virginia will be rain which might and as wet snow.

Now once   the  surface Low begins to rapidly develop it will  pull in colder air so that the mixture of rain / snow over the Washington, DC area were quickly change over to  snow  in Northern Virginia as well as DCA and into  Baltimore.  If the cold air gets into   the  Northern VA DCA the metro area in time …a few inches of snow could fall.

It is important to keep in mind that this is a fast moving cold front and the Low pressure area is going to zip rapidly through the  East coast.  This is one of the reasons why I am not forecasting significant snow amounts over the big cities of I95 from Philadelphia to Boston.   Another  main reason has to do with the storm track.  I  am not sure if the Low was going to pass close enough  to those  I-95  big cities  or develop into a significant system   that  drives heavy snow into  Philly  NYC   Northern NJ  CT and Boston    (Not  NO snow… heavy snow …   over  6″).

Beyond this event the models continue to show a strong piece of energy into southern Jet stream    that is going to develop a significant coastal Low over Georgia on January 22.  So in that regard the European model has gotten at least some of the general features of the pattern correct.  We   can  see the significant  Low pressure area off  the southeast coast here.    It is  THIS feature that the models were    focusing on last weekend for a possible significant East coast winter storm.

What  is killing the second storm– the Low off the GA coast on JAN 22  —from coming up the coast   is a another piece of energy in the Jet stream  that is diving SE from the central Rockies chords the lower Plains.  In the old days this feature would be called   “a kicker” because it drives the main piece of energy the or shortwave over the Georgia Coast EAST and out to sea.

Taking a look at the larger picture one of the reasons perhaps the primary reason why the big storm scenario   for JAN 22-23 which the models were forecasting on January 15-16… is not going to verify has to do with the overall pattern which is change significantly in the past seven days.

The High latitude blocking over Eastern Canada and Greenland is no longer there. And   NO model data of any kind  on the Morning   or   afternoon  cycles  shows any hint of this feature coming back before the end the month.  This has a profound impact on the overall pattern.  In some of the the weather forms which are out there on the Internet you will come  across some  Ignorant  weenie tried to argue that we don’t need to have high latitude blocking in place for east coast snowstorm patterns.

Not only is that not true but the Ignorant weenies  deliberately distort   the premise into something which is not     relevant.    The research and data is clear that at the time of the Noreaster  hitting the East coast we do not have to have a block over Greenland Eastern Canada  –    known as the      -NAO.      The issue  is getting the pattern to set up so that the coastal low becomes a snowstorm  and NOT a rain storm or Midwest storm.

The high latitude blocking which develops over Canada and eastern Greenland    the  -NAO…  affects the pattern in many different ways   when one is considering the potential for East coast winter storm.

In the days leading up to a  possible  East coast winter  storm…  the  blocking  often causes Low pressure  areas over  southeast   Canada to get  “trapped”    over   or close to  the New Foundland Canada.  This feature in the weather business is referred  to as a  NF  LOW or a  50/50  Low….(50° N latitude 50° W longitude ).       The combination of the blocking feature over Eastern Canada and Greenland   and the  50/50 Low  means  that the large cold arctic High which settles in over the Great Lakes and /or  New England stays in position and is not able to slide off the coast.  This means that the cold air stays in place over the northeast from North Carolina to Maine .

Without the blocking features over Canada and without the 50/50  Low  the  cold High  pressure  ares  do  not stay in postion   long enough to ensure an all snow event for the   coastal  Plains — from  Raleigh  to  Boston).  Now obviously the impact of the large cold High in position is much more important for locations such as Raleigh NC and Richmond VA   than it is  for  Boston and  New  England.

We can see the impact of this with the next potential event on January 25 – 26.      Looking at the weather maps initially on January 24  25 from the various weather models it would seem to be ideal or pretty close to ideal for a significant East coast winter storm to occur.

However all the models showed that the large cold High slides off the coast rapidly once the coastal low begins to develop.     Why does this happen?    There  is NO  50/50 Low and   No  Blocking over    eastern  Canada and / or Greeland  so there is No actual mechanism in the atmosphere to keep the cold High in place over the Great Lakes/ southern Canada  and or  northern New England.

But even besides all that… the blocking patterns are what good  meteorologists   look at  to see  if the   pattern is    ” setting  up”     for East  coast winter storms has further implications.

The jet stream maps from the various global weather models such as the European the Canadian and the GFS all show   at the surface low on January 25 it is going to come inland and track along the coast or very close to it.

Some of you may already be wondering if it  is possible that this Low  could be  shift its   track to the East a couple  of Hundred miles?   This is where the blocking patterns that we look for come  into play because   IF we had those features in existence over Eastern Canada and Greenland…  that any shift to the east would be favored.

Instead what we have is the merging or Phasing  of the    Two Pieces of energy  into one  BIG  trough over the  Midwest   because of    the lack of Blocking .

If we had the blocking over Eastern Canada and Greenland   then this phasing  of the  2 pieces   of  energy would  occur   East of the Mississippi river and this in turn would favor  the coastal Low  on JAN 25-26 tracking more to the east and thus increasing the chances of late all snow event.

But since we don’t have any that blocking —the phasing between the two pieces of energy  — occurs of much sooner  ( WEST  of the Mississippi River)    which  is    the  kiss of death sign for those wanting were or hoping for an all snow event on the East Coast.

Looking out to day 10  we  see   some HINTS  that  a  New  MIGHT  be forming  over    Iceland and the  UK.  WE  can  clearly see  significant  heights    building in the Jet stream.   often… but not alwways… when this happens  the Block  will retogreade into  Greenland.   So far NONE of the    11-15  day ensemble   are showing  this.  

 

1955   EST    JAN  16

Well it’s time to start talking about the next significant winter threat for the East coast.  And by that I am  not talking about the the January 18 event since that is a whole bunch of nothing.  Sure the precipitation still might start off as snow from   PHL to Boston but it IS   going to change over to rain on southeasterly winds… low level warming  temperatures  both at the surface  and all the way  to  850 mb.  Now some of you may look at the surface map from our morning or tomorrow evening and see this large cold High centered over southeastern Canada and wonder why  or how can the cold air possibly not hold in place   as the  southern Low  comes up the coast.

The first reason is that we don’t have any feature over southeastern Canada to  cause the the cold High to slowdown.  So it is  going to keep on moving rapidly to the east.  But in addition the event on Tuesday is going to consist of two areas of Low pressure–   one over the  Great Lakes and the   southern  Low  (which we can see the heavy showers and thunderstorms over the delta region this evening).     It is the “attack”  of  both  of these Lows which will help rapidly wrote the cold air just as the precipitation begins to move surge northward.   850 MB temps will  warm   to +3c  or warmer   even over  eastern  and southern New England.    In addition if you look at the   RH (relative humidity)   fields on the walk short range weather models you  will notice that there is large gaps in the precipitation coverage over  VA MD  and south  central  PA.

The main issue of concern and focused  from MY which really is on the   THREAT  of  significant  winter storm threat   for  JAN 21-22-23.

THREAT… not   yet a   fact or a  forecast

Once again we have the European models which had been the most bullish and aggressive on this feature and have shown the coastal development of some type on the cold front  for the past 7  runs.  And not surprisingly the operational GFS has been showing no such event of any kind –until early this morning and midday today.  And   the  Canadian model has been hinting at some sort of system developing on the cold front over the southeastern states  since Saturday.

Essentially what we are looking at are two possible scenarios.   The   new  strong cold front will drive through the Midwest into the Middle Atlantic states on January 20.  The front should drive fairly deep into the Tennessee Valley and the southeastern states by the morning of the 21st.  Arctic High pressure will move into position over Montreal.

At that point some sort of wave of Low pressure will develop on the front over the southeast states.  The interaction between the large cold High to the north and  this Low will set the stage for a classic cold air damming   event.

This image will show you what a COLD AIR  DAMMING event looks like on the weather maps and weather models.

We can see the   the  numerous thick   Black Lines  over  VC  NC  MD PA   NJ  having this funny  bend of  ” kink” in them.  The  appearance of   CAD is often but not always a sign of a significant winter storm developing but it does not tell us which areas could see the the significant snow and ice .   Many years ago weather models consistently over warmed the atmosphere at low levels during East coast storms and would prematurely forecast   a changeover from snow to rain.      However once the the phenomenon known as CAD was identified …meterologists were able to see this very clearly and the winter forecasts became a lot better when  it  ame to winter storms along the East coast.

THE  BIG  EAST COAST STORM   SCENARIO:

The last few runs of the regular or operational European model has been developing Low pressure over Georgia…  which moves to Eastern North Carolina on JAN 22 then   undergoes rapid intensification as a tracks off the southeast coast of New England.  In this sort of scenario  the model  has heavy ice over  northeast GA  western SC    much of NC  and   snow  from   VA to  southern Maine — including the big cities of the I   95 corridor.

The FLAT WAVE  SCENARIO  is supported by most of the other model data including the European ensemble . In this   set up a wet but rather flat looking Low pressure area develops  over the southeastern states and then tracks  ENE off the North Carolina Coast out to sea.

The following Models  support this   scenario.

12Z  SUNDAY  CANADIAN

12Z  SUNDAY  GFS

12S   SUNDAY   BRITISH/ UKMET

In  this particular scenario only North Carolina and Virginia would see significant snow and ice.  The precipitation would probably start off as ICE  then changeover to snow and   probably  no significant  snow  from DC northward.

Given the number of big storms which is hammered the Northeast US this winter  it is  easy to assume  that the big  East coast winter storm  scenrio #1 is probably going to turn out to be orrect .  And of course given the seasonal trend it’s hard to argue against that   the  BIG   East coast winter  storm idea.   But if we decide to use science as opposed to   weenie wishcasting…      the  last 3 big East coast winter storms have all occured with strong High latitude blocking over Eastern Canada and Greenland     (a  strong  negative phase of the NAO) .  That is clearly not going to be the case this time around and certainly not by January 20-21-22.

On the other hand if we do  end up getting   the  flat wave of Low pressure   scenario    then   there  COULD  be a problem with that northern extent of the precipitation.  We could end up seeing significant snow and ice storm over   NC and  only the  southern half  VA….  with very little winter precipitation falling north of Fredericksburg.

Right now I do not have a particular favorite— I am not biased towards one  scenario  or another one.  The change in the pattern in the jet stream over the Eastern Canada and Greenland should be significant in my opinion  so  as  to favor the flatter weaker way of scenario affecting only the Virginia North Carolina this coming weekend .

But on the other hand it sure is hard to ignore the seasonal trend which has been for big snow storms and the northeast US.