14 NOVEMBER  2007

 

  The Winter of 2007-2008 is going to be a mild Winter for most of the CONUS but it will be an active Winter as well.   The West Coast  (especially the Pacific Northwest)   as well as most Rockies and Upper Plains  will see the most active  of the Winter weather and has the best chance of seeing temperatures Below Normal.   For most of the Winter the Central Plains --  OK  to  NEB --   as  well as Midwest   is going to be  the  "battleground"  while the Deep South will feature  dry conditions and abnormally warm temperatures. In the Northeast US....  New England should see temperatures somewhat Above Normal  in the  General sense but  there will be   significant  cold intervals as well.   However the Middle Atlantic states including the big cities of the I-95 corridor from New York down to Richmond will see several bouts of   Above  and   Much  Above Normal temperatures.

 

The pattern will bear a striking resemblance to the Winter of 2005 -- 2006 and the Winter of 1970-71. In many ways this Winter will be a compromise between the two since I do not see the Winter 2007 -- 2008 as being as warm as the 05-06 Winter and not as cold or a snowy as the 70-71 Winter .

 

For those that have read my seasonal  forecasts  before  you know   that  there have been times  when  I have gone against the CF or consensus forecast   ( Hurricane season 2006   and  the  Winter  2005-06  just to name a few).  When I have done so   it is with good reason and for the most part  those contrarian Winter and Summer forecasts worked out quite well.   However in this particular instance   -- the   Winter   20007-08 forecast --  I think the CF  (consensus forecast)  is going to be correct.   That being said there are some surprises and issues which have to be dealt with.    As a general  rule   there have some  improvements over the last 10 years with regard to seasonal forecasting.   But  one the major sticking points I have with seasonal forecasts whether they are government or private forecasts   is that there is too much focus on    question   of  which areas  will see Above Normal  or Below Normal Temps  or the  precipitation  question and not  emphasis on  the underlying features.  WxRisk  seasonal  forecasts  are  premised on the idea that by focusing on more  underlying large scale weather features  a  more complete  picture or  "paradigm"    develops.  That is to say a more complete scenario of how of  the upcoming forecast is formed. The advantage  in doing   a season  forecast in this manner  is that it enables a forecaster to stay on top of any changes or surprises that might be developing as the  season  begins to reveal itself.

 

There are several critical assumptions which ALL  extended and long-range and seasonal forecasts are based upon. By emphasizing these features it becomes possible to develop that large-scale view of how I see the season unfolding and what to expect with trends. In the   Winter of  2007-87   these   Critical   features will be:

LA NINA... Currently the  Moderate La Nina  that  has  developed in  AUG   had  held  steady at  Moderate  levels  from Early  OCT   thru Mid Nov   2007.  The Moderate La Nina will hold its intensity   through  Mid  Jan...possibly   later.  There  is also the  issue of   when and How the  La Nina decays   from Moderate    to Weak  intensity  which could    have   significant impact  late in the  Winter and early in the  Spring  of 2008.

 

QBO  --    the  QBO is  currently in  the extreme  Negative Phase   (blowing  from West to East).  Its  two most  recent readings  (Sept   and   Oct 2008)  is the  2nd   most intense  East  QBO values  ever  recorded  and  and  are a  very close match  to the  Most   intense  East QBO  phase    of all time  ( Sept / Oct /  Nov 2005).    Moderately   strong East QBO   events strongly   support   Blocking  patterns  over the  North America  but  severely  negative  QBO values  strongly  support  progressive   weather patterns... restrict  large scale  Arctic  outbreaks and often play Havoc  with Model performance  in  the week 2 time frame .   More details  on this will be provides in the  full   report 

 

PDO  --  The PDO     or   "Pacific Decadal Oscillation"     a long-lived   climate  pattern   that    exists over the northern Pacific Ocean.   The  PDO Phase  involves the location  and intensity   of   large pools of  warm and /or cold   Seas Surface   Temperature Anomalies  (SSTAs)   in the  central and   eastern areas of the  Northern Pacific.   Currently the  PDO is  in a  negative phase or Mode   as there is a large areas of   Colder than  Normal  SSTAs  in the  Eastern  Pacific.  This  strongly  supports  the Mean trough  Position  in the Jet Stream over the    eastern Pacific/ West coast.

NAO-- The NAO or North Atlantic Oscillation is one of the major configurations  in the   Jet stream patterns  over   the Northern Hemisphere atmosphere.  The NAO   configuration covers a   geographical   regions from eastern or northeastern Canada to Greenland and over towards Iceland / Ireland and it is particularly important in Winter months  when it exerts a strong control on the climate of the Northern Hemisphere. There are several manifestations of the NAO  but  the feature is   extremely  hard to predict. There are  no Known    methods for doing so but over the last several years  there are have been some  "preliminary"  findings that some  some promise in this matter.  Last Winter   the NAO turned  strongly  Negative in Mid January and  Locked into  place   which set up a   dramatically   different   second half of the Winter   2006-07
(Jan 15- March 15)

SE DROUGHT  -   This is an unusual   feature for the  Winter 2007-08. The  severe  and  large drought    that developed  over the  Deep  South in the  Summer of  2007  has  continued    thru the  Autumn.  The features mentioned  above   (-PDO  Moderate La Nina    -QBO  etc)    tend to  support  the  Mean trough  position in the Jet stream over the  West   coast/ Far eastern  Pacific  at least through the  1st half of the Winter.   This in turns means that downstream of the  trough   thee is going to be a  Ridge which  might be located anywhere between  the  Lower Plains and  Bermuda.  However with the   large drought over the SE CONUS   will    focus the   Ridge locking into Place  over the   SE.

 

SEASONAL TREND  -- So far the seasonal trend has supported a progressive pattern over the northern hemisphere and especially North America. There has been very little high latitude blocking and very little sustained -NAO over Greenland and / or northeast Canada. Most of the storm track activity over the past 60 days has been over the Plains... upper Mississippi Valley... and Great Lakes. There have been a few significant events for the East Coast but only one classic Nor'easter. The medium and extended range forecasts from the various global climate models in the week 2 timeframe had been unbelievably bad... which is to be expected given all the above-mentioned parameters.  

The month of November 2007 so far has turned out to be fairly cold over the eastern half of the CONUS which has led some to speculate that we might be headed for a colder pattern in the Consensus Forecast is indicating. However the data clearly shows that November's that featured moderate La Niņa tended to feature a colder than normal November.

 

 

In the general sense the overall Winter pattern for 2007 -- 08 is going to feature the mean trough position being located  either over the  far eastern  Pacific /West Coast or the western third of North America and a mean Ridge position over the Southeast US.  The combination of these stronger than normal Pacific Jet stream... the typical climatalogical pattern one sees with a Moderate La Nina.... the pool of anomalously cold sea surface temperatures over the eastern Pacific (negative phase of the PDO)   and the effect of the extremely strong easterly phase QBO    (reminiscent of what we saw in the autumn of 2005)  will all contribute to ensure that the mean proposition is going to be located over the western portions of North America/ West Coast of the CONUS.

 

Since the basic laws of physics and meteorology say that for every Ridge position there must also be a trough.... the placement of the mean trough position over the West Coast means that   "downstream"   there must be a corresponding Ridge. That Ridge CAN be located somewhere between the Plains and Bermuda.

 

What determines  WHERE   this downstream Ridge position " sets  up"   can be several  factors. However going into the  Winter of  2007-8   we have an important and unusual feature which does not typically exists going into the Winter months. I am referring to the large and  intense area of the drought over the Southeast CONUS.

 

It is the position of  WxRisk    forecast  that  the Winter of 2007 -- 08 that the interaction between  above  mentioned seasonal  factors  ( Moderate La Nina  Very  strong -QBO  -PDO    and  the  late Autumn pattern)     along  with the large drought area over the Southeast will ensure that the downstream Ridge position.... which could be located anywhere from the Lower Plains east towards Bermuda... is going to  "Lock  in"  the mean Ridge position over the Southeast for much of this Winter.

There will of course be times when the Mean southeast US Ridge is almost nonexistent or playing a minimal role in the overall pattern. But on a large scale or seasonal perspective the ridge will be an important feature for this Winter.

 

 

DEC  2007  JET STREAM DEC  2007  PRECIP DEC  2007  TEMPS
JAN 2008  JET STREAM JAN 2008    PRECIP JAN  2008  TEMPS
FEB 2008  JET STREAM FEB 2008 PRECIP FEB 2008  TEMPS

 

Finally in the WHAT CAN WRONG ? department  we can  focus on during the middle and second-half of the Winter.  It is possible that the moderate La Nina may continue right through the heart of  Winter  and not begin to break down until late March or April. If that is the case there is not going to be any significant change  to the overall pattern in mid-or late February.

 

Another concern has to be the  weakening of  the strong easterly phase of the QBO which may occur late in the Winter and Spring 2008. The question is whether or not the weakening of the QBO will occur in time to affect the last third or 25% of the Winter season. WxRisk   believes  FEB  and MARCH 208  will be  the coldest /  stormiest   portions of the  winter for the eastern   Third of the CONUS.

 

And lastly the October monthly reading of the NAO was positive. There is some indication that suggests a correlation between the October NAO phase and the inverse or opposite phase during the Winter months. If during the Winter months there is a sustained negative phase of the NAO over Canada and Greenland... there could be major shift in the overall pattern with the Northeast US turning quite stormy and cold.