0800 14 NOV  2011

If it wasn’t clear last week in the weather models… it certainly is clear now:     there is  little chance of a turn towards a significantly colder  pattern over   any portion of the CONUS before December 1.  Again that in itself is not that unusual   per se.  But obviously as we move towards Thanksgiving and  the last   days of VOV  there will   be a big emphasis on whether or not we are going to see a significant large scale pattern change.  Last December that  is exactly what happened…  but  back in 2007-8   the   pacific jet   never let  up  and all of the DEC    cold in the    eastern  CONUS forecasts busted horribly.

In  looking at the “overall”   pattern I do see some changes of current  pattern. But with respect to affecting sensible weather conditions  in the  Conus….  there  is  not much to get excited about if you like cold weather.  It  is important that as a meteorologist we communicate in a clear and effective manner.  So while I can talk about changes occurring in the overall pattern at the high latitudes which over the long term could be more positive towards   getting a colder  pattern… the fact  is that  for most people this will sound like a bunch of esoteric   gobbledygook  because  their forecast shows  more  mild  temps. From the  average person point of  view   there  appears to be  no significant change in the overall pattern.

If we compare the current hemispheric  500 MB  map   as of 0z NOV 14   to the one from  NOV  7 we do indeed see significant changes.   The  PV has split which is what most of the models were  e forecasting and we now have one of the PV centers moving into far northwest portions of North America    (the  north  slop of    eastern Alaska/ Yukon).   The   other  PV has  retrograted and is now moving towards the north side of central Siberia on the arctic circle.   And we also seeing the widespread introduction of arctic air across all of Central  and Northern Canada which is something we did not see last week  or the  week before.  This is leading to increase in snow cover across Canada as well.  

 Another key aspect to the overall pattern is the powerful European or Scandinavian  Ridge.  Last week most of the model data show this Ridge  retrograting  into Iceland   or Greenland  but clearly that is not happening on any the model data over the weekend or this morning and that’s one of the reasons why the pattern change at the high latitudes is not working its way down to the mid latitudes.

Part of the problem is that the new polar vortex over Northwest North America splits into two sections. The  Eastern   portions  slides to Eastern Canada by the end of the week and moving towards Baffin island and the Davis straits by Day 7.  This movement initially causes a  moderate   trough to develop over the eastern CONUS   but once this feature moves into Eastern Canada were labrador in actually  cuases the NAO  to  flip  back to Neutral or  Positive and it also kills any chance of the Scandinavian   ridge   retrograting to Iceland.

This is reflected in the the  Teleconnections  Indicies…   http://raleighwx.americanwx.com/models/00zlinegraphs.html

However the western portion  of the  North  American  PV…. continues to move from the north slope of Alaska southeast into the gulf Alaska and along the Alaskan panhandle  by  day 3.  This feature slides down towards Vancouver Island and the Pacific Northwest    by day 7.     It  is a very intense vortex and if this was the middle of December  there is no doubt that this feature bring a major snowstorm to locations such as Vancouver and Seattle.  It still might give an how  impressive this feature is.   A piece of this energy  breaks off and develops  a  significant surface Low  that tracks of the western high plains this weekend with the arctic air pressing south across sea was Canada border into Montana and the Dakotas.  This will probably be the first serious winter storm for the Upper Plains of the season  — there was a moderate one last week .

By day 10  the  operational European and the European  ensemble show a dual center pattern with one PV  over central Siberia and the other one located over northwest Canada –perhaps in the Yukon. The PV  over   the  Yukon is clearly was stronger on most of the model data with  its  value     below 500 DM .   The Teleconnections from this intense vortex over far Northwest North America of course supports a strong southeast U.S. to ridge so all of the Model  data here  apears to be  very consistent and  meteorologically sound. 

In addition if you take a look at the  500 MB   height lines over the north Pacific you will see that the extremely strong central north Pacific    positive   height  anomaly  — the   Ridge   at 588dm– is located surprisingly close to the   498  dm   very strong and negative  height anomaly over the Yukon.  This of course is causing the Pacific jet to become squeezed causing ncreased  velocities to a extremely powerful  180 knots on the 0z GFS   at 192 hrs.    And  having the jet streak slam into    the  West coast  / br Columbia   ensures the mean trough stays on the West coast and  the  the cold air   building Canada  cannot possiblly   drop south of the   US Canada  Border .

Clearly the impediment in terms of getting the pattern to turn significantly colder is the extremely intense polar vortex over the Yukon.   This  fat  pig   has  got  to MOVE  or slide    southeast into   north central  Canada.  As long as that feature  is in  that part of the western hemisphere the pattern is absolutely no chance of changing.  This position for a  PV  has   long been know  as the Kiss of  death if one is forecasting any sort of sustained colder outbreak were pattern developing over the eastern half of North America.  Of course there have been plenty of winters where the vortex up there in northwest Canada in November has moved  to the southeast  which ends up altering the entire pattern.  But as long as that feature  is  there and the 180  knot    long jet streak ….     the central and eastern  CONUS stays Mild.