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
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.
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
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 are1950, 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.
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
However the 3 years selected as Analogs are a very small sample base and should NOT be countered on too heavily.
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
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.
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.
The average JAN-FEB-MAR APRIL PDO INDEX is the most negative in +30 years .
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.
These analog years produce the following anomaly Maps
These analog years show Much
drier than Normal over a portion of the WCB (western
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
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...
The 2006 Hurricane forecast
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.
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.
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. 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. 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. 3 or 4
Tropical cyclones in the Gulf... 2 canes 1 Major
(west side of FL= Gulf)
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.
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.
STORMS.... 16 of which 9 will be
Hurricanes and 3 intense Hurricanes.
3 or 4
Tropical cyclones in the Gulf... 2 canes 1 Major
(west side of FL= Gulf)