***  Issued   privately 5/ 16/08  ***

 

This Summer 2008 forecast will be heavily based upon the weakening of the current La Nina which has been one of the dominant... if not THE dominant feature... affecting North America's weather patterns over the past 9 months. How fast the La Niņa decays will be a critical aspect to this Summer forecast as well as any other Summer forecast that you may come across. There are going to be other factors for consideration as well with the primary ones between the development of the strongly negative PDO in the eastern Pacific and the saturated ground conditions over the Midwest and Northeast.

 

 

While the data continues to support the idea of the La Niņa event weakening to neutral conditions by the middle of Summer there is a possibility that the La Nina event could linger right into August or September as a very weak but still noticeable phenomena. Typically this sort of uncertainty could be important because there are significant differences in the overall weather pattern in the Summer months between La Niņa and neutral conditions.

            

 REVIEW   OF SPRING   2008

  The link below shows the WxRisk  SPRING  2007-08 forecast  MAPS. The  actual  Summary   said this

    The Spring season of 2008 is going to be dominated by the continuing strong La Niņa event which has been raging since last Autumn across the equatorial Pacific. Moderate and strong La Nina events in the Spring season have a strong correlation to particular types of weather pattern for the Plains and the Midwest.    This specific  Spring  time  Moderate / Strong La Nina   Pattern  features Below and Much Below Normal temperatures and Above Normal rainfall especially across the Midwest and into portions of the Deep South.

  If you would  compare  these Maps to  ACTUAL  Maps  section -- see Below-- this was  a VERY  good  SPRING forecast.

 JET STREAM MAPS:  The Jet stream  Maps   for all 3  months...especially so   for  APRIL  were  very good. 

TEMPERATURES:     For  MARCH my Temperature   Forecast  for was  GREAT  as I  correctly   forecasted the  Below Normal temps over the   Pacific NW and  Northeast  and  the   warm   temps over the   SW and Lower Plains.   In APRIL I    totally Missed  the  warmth over the Northeast   but  got the  Below Normal  temps over the Pacific NW correct.  IN MAY ...  thru MAY 16  I  appear to have gotten the large area of Below Normal temps over the   Rockies and Upper half of Plains  partially  correct SORT  But I have   the area  of  Above Normal temps   TOO far to the North.

 PRECIPITATION:  for MARCH   the rainfall forecast was   good   BUT I missed the  Above  Normal Rainfall   area   over  the Tenn Valley and Delta.  I did  get the  Dry area over the West   correctly.  In APRIL I had the  Below Normal area  too far into the  Central Plains and   near the  Lower Mississippi river... which was  VERY wrong but the  Above Normal rainfall area    over the Midwest and Northeast  was spot on.  For MAY...  I  forecasted a  developing  area  of Below Normal rainfall  over the  central Plains  which  might be correct But I have the    Above  Normal  rainfall area too far to the south and   east.

    Click HERE  to see the  Full SPRING 2008   FORECAST

 

 MARCH JET STREAM    MARCH   TEMPS   MARCH    PRECIP
 APRIL JET STREAM   APRIL  TEMPS   APRIL  PRECIP
 MAY JET STREAM    MAY   TEMPS   MAY   PRECIP

                  ACTUAL                                             

                     

 MARCH JET STREAM    MARCH   TEMPS   MARCH    PRECIP
 APRIL JET STREAM   APRIL  TEMPS   APRIL  PRECIP
 MAY JET STREAM    MAY   TEMPS   MAY   PRECIP

 

 

     SUMMARY OF   SUMMER  2008 FORECAST      

  The Summer pattern of 2008 will be one which features a slow drying trend during the month of June and a shift to a significantly drier and warmer pattern than Normal for the latter half of July and August. The wet pattern we have experienced during the Spring of 2008 is breaking down as the La Niņa event continues to decay . For a while the saturated soils over the Midwest will tend to keep the Mean trough position over the Midwest or eastern third of the CONUS. Once the La Niņa event has ended... the blocking pattern over eastern Canada will break down or simply move away which means that the rain events will become more infrequent allowing for more drying over the Midwest.

By the middle of Summer the dominating feature will NOT be the La Nina but the large pool of cold SSTs -sea surface temperatures- in the far eastern Pacific. This phenomenona is known as the negative phase of the EPO.   When the EPO is strongly negative it strongly supports a pattern that features the Mean trough over the far eastern Pacific and/or a West Coast... and correspondingly a Ridge downstream ... which in this case strongly implies a Mean Ridge position over the southeast or Midwest. This sort of pattern will allow for a significantly drier and hotter pattern than normal east of the Mississippi River in the second half of the Summer.

  

JUNE  2007  JET STREAM JUNE   2007  PRECIP JUNE  2007  TEMPS
JULY 2008  JET STREAM JULY 2008    PRECIP JULY  2008  TEMPS
AUG 2008 
JET STREAM
AUG 2008  PRECIP AUG 2008  TEMPS

 

   DISCUSSION  OF   SUMMER  2008 FORECAST  

 The weather pattern we have seen over North America during the Spring of 2008 is essentially the same weather pattern we saw for most of the winter. A very strong Pacific Jet has been dominating feature combined with the strong La Niņa and this has kept the pattern very active with the Pacific Northwest... the Plains and the Midwest rather cold and stormy. The very wet Spring is simply a continuation of the very wet and snowy winter much of the Plains and Midwest experienced.

The typical pattern during a moderate or strong La Nina features two distinct features. First we see an active Pacific Jet which means a mean trough position either over the eastern Pacific and /or along the West coast. This results in temperatures running below normal over much of the Pacific Northwest and northern Rockies as well as portions of southwest and south central Canada.

However when there is trough over the West coast it means that you have to have a Ridge "downstream" which in this case means a ridge over the southeast states or just offshore.

The second important feature of a moderate or strong Spring La Niņa event is the higher than normal probability of blocking patterns developing over central or eastern Canada. These blocking patterns have a tendency of keeping the same overall pattern in place for weeks at a time and indeed that has been very much the case for the Spring season of 2008.

The blocking pattern situated over eastern Canada in the Spring of 2008 has been acting as a suppressing mechanism for the Ridge of the southeast. As a result the systems which have been coming into the West Coast are tracking further to the south and east than they normally would and this has resulted in the abnormally wet Spring for much of the Midwest and the Northeast.

The key is the decay and collapse of the La Niņa event early in the Summer of 2008. The decay of the La Niņa means that the blocking feature over eastern Canada will be gone and as a result we will see a basic or typical pattern that features rainfall events at longer intervals.

Climate research shows that saturated soils over large areas can influence the overall pattern of troughs and ridges positions through a process known as trans evaporation. This is considered to be a positive feedback mechanism. Euphemistically this idea is expressed in the well known phrase drought begets drought and wet patterns beget wet patterns. As a result even though the pattern in June will turn Drier the wetter than normal ground conditions over the Midwest will still tend to support the mean trough position over the Midwest and Northeast. The drier and warmer pattern will allow for significant drying over the saturated areas of the Midwest during the month of June.

For July and August the pattern will essentially be a basic one which features the trough on the West coast and the Ridge over the southeast and Lower Midwest. The Rockies and the Plains will turn hotter and drier much sooner in the Summer season and last for much longer period of time since the mean Ridge position could be over the eastern Rockies or Plains.

 

   ...THE   DECAYING  LA   NINA...   

  

  This next map  is presented  so that   the reader can   more  easily  comprehend  that La
Nina and El Nino events occur within a certain geographical region along the equatorial Pacific Ocean.      The  ENSO  region   consists  of   several sectors .... ENSO 1+2   ENSO   3    ENSO  4   and   ENSO  3.4.   Officially  an El Nino or La Nina event is declared when the SSTA     (sea  surface temperature anomalies)    have reached a certain level for a 5 month time period   over the   ENSO   region known as    3.4 .

 

  

   

  

 The various international weather agencies around the Pacific-- including the US' CPC as well as the Japanese and Australian weather services have standardize the definitions of what constitutes a La Nina and El Nino event. There are several different criteria one can use but the most important one has to do with the region known as ENSO 3.4.

In the Period from JAN FEB MARCH 2008 the numerical value of ENSO region 3.4 was -1.4C . Since the La Niņa is dying and come to an end  by JUNE 2008 it is going to be important to look at other moderate or strongly Nina events of similar intensity doing the period of January February and March... and observe what those Summer weather patterns were like.

 Since 1950 there have been  6 Seasons which featured La Nina events with a ENSO region value of -1.4c or lower.    These years    are   1950, 1971, 1974, 1976  1989, 2000.

These  two images  from  the    IRI  center    show the  APRIL 2008   and MAY 2008     forecasts for the  current  La Nina event. AS you can see  MOST of these climate models  show  the La Nina either  holding  barely  at   Minimun threshold   for WEAK La Nina Status  OR  show the La Nina   weakening to  Neutral   by  the Summer and  early  Autumn  of 2008.

 

APRIL 2008  FORECAST MAY  2008   FORECAST

   

   This   in considering the  Analog La Nina years   of 950, 1971, 1974, 1976  1989, 2000  some of those years  features a  La Nina   event that  continued    thru the Summer and into  the  Autumn and Winter Months  ( 1950  1971 1974) .   As  I stated   above   this forecast  is   based on the  CRITICAL   Assumption that the  La Nina  event  that is  currently  weakening  continues to do   and end  in JUNE 2008.

  Therefore the   Analog La Nina years  are 1976 1989  and 2000. In those  Years the Moderate to Strong  La Nina of the  previous Winter   died  by  the  Summer season.

   These  3 analog   years   seem to show Much drier than Normal  over the  WCB  (Upper Mississippi valley) ... slightly  wetter than Normal  over Ohio valley and  much wetter than Normal over the    Northeast.... and Hotter  than Normal  the  Rockies   Upper Plains ... and    cooler than Normal over the   Lower  Plains  into the  Ohio valley and Northeast

PRECIPITATION  ANALOG
1976   1989  2000
TEMPERATURE ANALOG
1976   1989  2000

 

  However  the   3 years  selected as Analogs  are  a  very small    sample base and   should NOT be countered on too heavily.

 

 

...SOIL   MOISTURE CONCERNS...   
  

 Ask any farmer and he or she will tell you that the old wise phrase drought begets drought has a lot of validity to it. There is a lot of scientific reasoning and basis of for this concept. Its called Evapotranspiration.

There is a lot of research over the last decade showing that there is a strong connection between large areas of excessively wet and excessively dry ground conditions and the impact it can have on the general atmospheric circulation
patterns. Interestingly enough with all the focus on some of the newer indices and ideas in in climate / seasonal forecasting this rather a well-known phenomenon is often neglected by seasonal forecasters.

That being said one has to be careful in how one uses this idea that excessively wet or dry ground conditions over large areas can affect the general atmospheric pattern. Often times it will be a common addition of an excessively wet or dry area over a particular region combined with some other important factors such as a La Nina event that will help shape the overall pattern.

This first image represents a long-term drought and moisture conditions across the 108 different climate zones in the CONUS.   By LONG TERM TERM we are referring to the last several months as well as recent weeks. As you can see from this image much of the Midwest into the Northeast has been excessively wet ... while the good which was very intense over the southeastern US is still in place but its not nearly as intense when compared to what we saw last year.

The short-term climate trend shows the impact of the wet spring... and the dry conditions over the Southwest.   We can see that the trend over the last few weeks has been for the ECB and the Northeast has been towards less and less moisture/ precipitation. Over the southeast states precipitation has been moderately below normal but again not as severely Below Normal as what we saw in the Spring 2007. Over West coast the Short term trend is much Drier. .

Thus we can conclude that indeed the Northeast and Ohio Valley regions ARE drying out but still have a ways to go.

The implications of these maps are significant. The excessively wet conditions we see over the Midwest and the Northeast continue to support the mean trough position being centered over the Midwest and the Northeast for the first portion of the summer. However the drying trend that were saying in the short term map also indicates the that the excessively wet conditions have come to an end.

Of deeper concern are the dry conditions over the Deep South which continued to show Below Normal rainfall even in the short term. This may have more significant implications down the road in the second half of the Summer.

 

    

            ...THE STRONG  -PDO  EVENT...   

 

Over the  last   10 years there has been a significant amount of   research  done  on a   climate pattern   that   is   called the  PDO in the weather biz.  The PDO     or   "Pacific Decadal Oscillation"     a long cycle  climate  pattern   that    exists over the northern Pacific Ocean. 

The  PDO   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.  Why is this important? Again     research  has  shown that large  areas  of   warm and cold  water   pools     called     SSTA  couplets    STRONGLY affect the    Jet stream pattern and the   positions of    Ridges and troughs  within   the Jet Stream over the   Pacific   and  western North America.

This is   diagram   shows    you    the Two phases  of the   PDO... the      BLUE  color    represents   very cold  SSTA...    the  Green    cool SSTA....   the    RED color  very  warm SSTA and the  Yellow   warm SSTA.

pdo_warm_cool.jpeg (194655 bytes)

 

 

 The map below explains     HOW  and  why the   PDO affects the pattern   across  North   America.  Click on the Maps to see the     Full  size.   As you can see when the PDO is in the Positive or WARM  phase... the warm sea surface temperature anomalies along the West Coast North America strongly supports a  ridge developing over the western portions of the continent and locking this Ridge in   place.    Of course if you have a Ridge over the West Coast then downstream you have to have a trough.... (for every action there is the equal opposite reaction)... which in this case is over the eastern third of the US. This pattern is known as the +PNA and it is the classic signature for a cold weather pattern. The arctic air masses from the Arctic regions and northern Canada follow the Jet stream down into this trough which results in sustained intervals of below row temperatures cold water. On the West Coast the Ridge of High-pressure means clear skies very little storminess and Above normal temperatures.

 However the opposite is true what we had a negative or cold phase of the PDO. In this case the warm water is located out in the Central Pacific Ocean and cold water develops along the West Coast North America. This results in the jet stream developing a trough along the West coast... and of course downstream a Ridge develops over the eastern half the US. This sort of pattern results in a very cold and stormy West Coast with areas such as a Seattle and Portland saying snowstorms in the very strong cases out of the negative phase PDO... and the central and eastern US saying below normal precipitation and above mobile temperatures.

 

SCHEposPDO.jpg (132518 bytes) SCHEnegPDO.jpg (142521 bytes)

 

    The average JAN-FEB-MAR APRIL PDO   INDEX is the most negative in +30 years .  

  JAN 2008 FEB 2008 MARCH 2008 APRIL 2008
-1.00 -0.77 -0.71  -1.52

 

PDO    AS OF MAY 10

  

 These TWO maps show the current ocean water temperatures from around the world. They are Both from MAY 10 and they essentially show the same thing... and on the left is from the UNISYS web site and the map on the right fro NASA. The important thing here is that pay attention to what is going on in the Pacific Ocean and specifically the large pool of very cold waters running from the Bering Sea down to the Gulf of Alaska off the West Coast of Canada off the West Coast of the US and then out into the Pacific off the Baja California.

That sort of ocean temperature configuration clearly supports a classic looking and very strong -PDO event.

 


   The  Link  that shows the raw data is HERE   http://jisao.washington.edu/pdo/PDO.latest    What we  are Looking for   4 Month   intervals  with SIMILAR    numerical   values.  The Following years are  clear   matches   to  the   PDO   values of JAN to APRIL 2008
  

  1950 1952 1954 1956 1962 1968 1971 1972 1974 1975 1976 1991

  These  analog years   produce  the following  anomaly Maps

PRECIPITATION  ANALOG   TEMPERATURE   ANALOG

  These  analog   years   show Much drier than Normal over a portion of the  WCB  (western
Mississippi valley) ... slightly  drier  than Normal over the portions of  the  ECB.   For Temperatures   these analogs clearly show a large area of  Below and Much Below Normal  temps over the Western third of the CONUS ... Above  Normal  temps   over the   Central Plains. 

 

 

 HURRICANE  SEASON   2008

  For the last 3 seasons the WxRisk hurricane seasonal forecast has been nothing short of spectacular. In June of 2005 the WxRisk seasonal hurricane forecast that predicted historic hurricane activity for the Gulf of Mexico was picked up by Dow Jones and Bloomberg news services... as was the 2006 and 2007 seasonal Hurricane forecasts which called for below normal activity when the vast majority of the consensus forecasts were calling for more Avove and / or Much Above Normal  activity.

The   2007   Hurricane   forecast

  http://www.wxrisk.com/Seasonalforcst/SUMMER2007/summer2007.htm

  This time around WxRisk.com does see an INCREASED   probability  of  significantly More  active Hurricane season for 2007 . However where I disagree with the consensus forecasts  is the   subject matter   of which   regions of  the    US Coasts   are more likely to be hit.... ( Gulf / Florida / SE US coast / NE US CONUS).    I see a much reduced chance of  the central and eastern  Gulf  as well as the   SE Coast and the     Northeast  coast being hit   as well  a much reduced chance   of central and northern portions of the Texas coast being hit this year....  with an increased chance of areas from Brownsville /southern TX   southward  into northern  and central Mexico getting hit ...   Nor do I see    the  2007 Hurricane as  a  New England    year either...

   Note  Hurricane  DEAN and FELIX  both category 5  Hurricanes   both  stayed well south  hitting   the Yucatan and Mainland  Mexico....see the  GREEN  track

 

The   2006   Hurricane   forecast

  http://www.wxrisk.com/Seasonalforcst/Summer2006/summer2006.htm
 

    The Hurricane  season of  2006  will NOT be nearly  as bad  as  many forecasters are  forecasting.  WxRisk  is calling for  ONY 13  named   Tropical  Cyclones...  and it could less than that IF   an El Nino  event develops  by  AUGUST 2006.    The 2006 Hurricane season  will be nothing   like the  severe Hurricane  activity  in the  Gulf we saw in 2005 .   WXRISK   also   strongly  disagrees with the  assertion  made by  some other  well known Private weather forecast services that  the  East coast   will see an increased chance of seeing   several  Land falling   Hurricane  or near Misses  in 2006.  In fact  WXRISK sees a late Summer   early  Autumn  pattern that  makes  such a  forecast  extremely unlikely. 

  

  There been several reasons why the last two hurricane seasons have not lived up to expectations.

The primary reason is that while it is true that the Atlantic Basin is currently in a super active phase and has been since 1995 that does not mean that every single year is going to feature above Normal activity. Clearly after the super active hurricane season of 2005 many private and government forecasters believe that it was a "given" the the that the 2006 and the 2007 hurricane seasons would have at least a normal amount of hurricane activity. it never occurred to them that something might be going wrong and that there should be no base assumptions.

Another words it's been a classic case of group think and it's one thing that WXRISK.COM really hates its group think.      ( Weather is suppose to be Science NOT a Gallup poll).

On a meteorological level the Azores HIGH has stronger than Normal in the 2006 and to a lessor degree the 2007 hurricane season. When the Azores High is stronger than Normal it  has  3 important   affect.

  1.  It causes UPWELLING -- a process where warm SSTs get the displaced by colder SSTs  from below the Ocean surface. These colder SST anomalies damper Tropical wave development.      
  2. The   stronger   than Normal Azores High helps to suppressed rainfall over sw Africa. With less rainfall the DUST problem (called the SAL in the weather biz) became a real problem for strong Tropical waves as they moved off the sw African coast.
  3. The stronger than Normal Azores HIGH enhances the Low level easterly winds over the tropical Atlantic which carries  the Dust far out into the the Tropical Eastern Atlantic .

Case in point: the two category 5 Hurricanes that hit Mexico BOTH came off the sw African coast at near 10.0 north Latitude which enabled these systems to avoid the cold waters and high Dust levels. And other Tropical waves that came off of the African coast pretty much died. 

    THIS   SEASON:  the  Azores  High is NOT stronger  than Normal and rainfall over the Sahel  has been close to Normal.  

  This IMAGE shows the current sea surface temperature anomalies for the middle of May over the entire Atlantic basin.

   As you can see the sea surface temperature anomalies are actually quite warm in the far eastern Atlantic which is indicative of less upwelling than what we have seen over the past couple of hurricane seasons and is supportive of the idea that the 2008 hurricane season could see Above Normal activity over the Cape Verde Island / far eastern Atlantic .

 However  the  Seat Surface  temps  over the Caribbean basin and over  the southwest Atlantic  and  gulf of Mexico remained rather chilly. The sea surface temperature anomalies here are Below Normal but not especially so and it would not take much to get these cold anomalies to warm up.

  

    Taking a look at the various analog years from both the PDO discussion and from the decaying La Niņa discussion... I have called up the corresponding hurricane seasons to detect what if any sort of pattern we can see from these years.

 

 1950 1952 1954 1956 1962 1968 1971

 

1972 1974 1975 1976 1989 1991 2000

            

  There are some rather interesting statistics and trends.

  • Only  the 1950 1971 and 2000 Hurricane  seasons  featured Above Normal activity.
  • Only the hurricane season of 2000 featured as many as 15 named storms.
  • The seasons of 1954 1974 and 1976 featured 11 named storms
  • All of the other hurricane seasons featured Below Normal activity!

And taking a look at the actual seasons and their tracks... from these 14 various hurricane analogs we see some activity in the Gulf of Mexico but not a lot.

  •  7  of the 14 analog years featured either NO  hurricane activity or only 1 hurricane in the Gulf of Mexico...
  • 3 of the 14 seasons featured only 2  hurricanes in the Gulf.
  • Only the 1950 1956 and 1968 hurricane seasons featured three or more named hurricanes in the Gulf.

 The analog Hurricane seasons are showing a clear trend that the odds are NOT  good that the Gulf of Mexico is going to see an Above Normal hurricane activity in the 2008.

The analog seasons also appear to support the idea of a lot of activity along the Southeast US coast or over southwest Atlantic just off the southeast coast and through the Bahamas.

  There will be  Above  Normal Cape  Verde   Hurricanes / Tropical  cyclones... hence the  threat to the Bahamas  FL and the SE  coast... IF -- and ONLY  IF... the     trough  over the Midwest and  NE is gone   the  Hurricane  season of   2008  could see   Above  Average   SE  landfalls.   

  TOTAL  NAMED  STORMS....  16  of which  9   will be Hurricanes  and  3 intense  Hurricanes.
Of the  16

    3 or 4  Tropical  cyclones  in the  Gulf... 2  canes 1 Major  (west side of FL= Gulf)
    6  Tropical  cyclones   for the  SE  coast area  3  landfalls   3 near misses( passes within
        200 miles of coast ... 3  canes  3   tropical storms
    No   signal one way or the other  at this time for  New  England   hurricane threats