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SUMMER 2010 REVIEW
REVIEW issued 20 OCT 2010
There is an increased RISK (Not probability just RISK) of a DROUGHT in the 2nd Half of the Summer into Early Autumn over the some portion of the Midwest and Deep South.
For the better part of the year the weather pattern across North America has been persistent and unyielding. From the Spring of 2009... through the Summer... Autumn and into this past Winter we have seen the same pattern stayed locked in.
The pattern has featured a persistent Trough in the Jet stream and persistent blocking in the High Latitudes over Eastern Canada and Greenland. The blocking pattern during the Autumn of 2009 and Winter 2009-10 reached record levels ... Stronger and more persistent than any other high latitude blocking in six month period since meteorologist and climatologists started keeping track of blocking patterns (back to the 1950s).
In addition at times this pattern has also been aided by a persistent ridge over Western Canada AND the Moderate / strong El Nino event (known as a WARM ENSO event in the weather biz) that developed in the late Summer of 2009 and lasted right through the Winter of 2009-10 into the early Spring of 2010.
The combination of these four factors has produced large areas of persistently Below Normal and Much Below Normal temperatures over the Plains the Midwest and northeast Conus. The pattern over the past 12 months has also been a persistently... and at times... excessively wet one with many areas across the Plains and the Midwest experiencing Much Above Normal with respect to soil moisture and the soil saturation. Many areas from the Plains to the Northeast have seen ground soil conditions that have been super saturated for months at a time.
Agricultural traders can be easily recall the excessively wet Spring of 2009... the record cool Midwest Summer... and the record shattering cold and wet September and October in the Autumn of 2009.
KEY ASSUMPTIONS & PREMISE
That pattern is over and something new is developing. The evidence for this is apparent already in the spring 2010 season and in the changes of the overall hemispheric pattern. SPECIFICALLY:
THE BOTTOM LINE is this: the old weather pattern that has dominated North America is over. It is dead. Something new is coming. Any Summer2010 forecast that that was premised on the idea that the weather pattern of the past year would continue... is going to bust.
WHAT WILL THE NEW PATTERN LOOK LIKE AND WHAT WILL IT MEAN?
Without a doubt the overall driving factor for THIS Summer 2010... and ANY forecast for the Summer 2010 has been the status of the El Nino. Most of the long range computer models which forecasters rely on to get an idea of the El Nino and its trends in the future... have consistently showed that the current El Nino would continue through the Spring and slowly fade over the Summer of 2010.
That assumption is wrong. As you will see the El Nino is weakening RAPIDLY. Thus ANY Summer 2010 forecast issued back in March or early April are therefore premised upon a key factor which is no longer likely to occur.
The data over the last few weeks shows a rapid weakening of the El Nino. The new climate models are showing a strong trend for the El Nino to drop to Neutral conditions early this Summer and shift into a La Niņa event which develops in the second half of the Summer of 2010. The new data shows La Nina has a good chance to become a Moderate La Nina event by early in the Autumn 2010.
This WxRisk.com Summer 2010 preview forecast is based strongly on this trend. The European El Nino forecast model based upon March 1 show a strong trend the SSTA (sea surface temperature anomalies ) developing over the El Nino regions starting in July and becoming moderate by August September and October. The NEW updated version of these forecasts in SSTA (April 1) show a even more rapid trend towards a La Nina event.
Significantly back in the month of March most of climate models did NOT agree with the European climate model that showing the rapid cooling over the El Nino regions. However the new April climate models are now significantly colder and have moved much closer to the European Model of a moderate La Nina even developing in the 2nd half of the Summer and into the Autumn of 2010.
WHY is this significant? There is a strong correlation between the development of drought conditions over some portion of the Plains and or Midwest and Moderate or strong La Niņa conditions.
Since 1999... when WxRisk.com began seasonal agricultural and energy forecasting I have never forecasted a drought... or the risk of a drought over a significant portion of the Midwest. Unless the data changes.. when I issue the official Summer 2010 forecast... ( about 5/20/10) I probably will be forecasting a high a risk or threat of seeing a significant drought LATE in the Summer into the Autumn of 2010.
We may already be seeing the beginnings of this new warmer & drier weather pattern and how things COULD evolve into a potential Drought pattern. The development of the persistent trough over the West coast has brought California... the Pacific Northwest and much of the southwest states a pretty nasty chilly Spring 2010 with Below and Much Below Normal temperatures and Much Above normal rainfall. This image is a cleaned up map of this European Model analysis of the atmosphere from Mid April.
EURO MODEL OF ATMOSPHERE VALID APRIL 15
As I said above this is a fundamentally different pattern from what we have seen over the past year across North America.
Because it is still early in the warm season... the parade of Low pressure areas coming out of California are tracking ENE through the central Rockies and into the Plains and the Midwest. Therefore in terms of sensible or "actual" weather it appears that the pattern is still staying stormy and wet.
However... in response to this persistent trough over the West coast ...the atmosphere has countered this by developing a ridge in the Jet stream over the Lower Plains and the Deep South. This has resulted in warm conditions over the past 45 days with respect to temperatures which have been running Above normal over the lower half of the Plains the Deep South and Midwest and somewhat Below Normal rainfall.
As we move into the late Spring and Summer the persistent trough over the West coast will shift to the north because the main jet stream position always shifts to the north as we approach the Summer season. This means that eventually the Low pressure areas that are Now coming out of central and Southern California will instead into come out of Northern California and/or Oregon. These systems will still track ENE but instead of moving through the central Plains then into the Midwest ...these weather systems ENE track will take them across and northern Rockies and into Southern central Canada and perhaps the Dakotas and western Great Lakes.
To the south the Ridge which is currently centered over the Lower Plains and the Deep South will begin to expand to the north and west as the jet stream shifts to the north and west. This will allow drier in warmer conditions to develop during the late Spring and early Summer.
As the La Nina strengthens and kicks in... The ridge over the Deep South will continue to strengthen and expand. This sort of scenario is based on a classic moderate La Niņa drought scenario.
One of the most overlooked aspects to forecasting seasonal weather patterns has to do with soil moisture. I Am not sure why this is the case but a lot of seasonal forecasters and climatologist often overlooked the impact that large areas of the excessively wet ground or super saturated ground and large areas of very dry or drought conditions can have on the overall pattern.
For example the great drought in the Summer of 1988 followed a very dry winter of 1987-88 and Dry Spring of 1988. These are all part of a strong La Nina event.
In using the soil moisture conditions and patterns as a clue as to what the upcoming season might look like one has to be careful. Using the soil moisture method for seasonal forecasting really only works IF and only IF... you have large areas of excessively wet ground / soils and large areas of excessively dry soils.
Let's take a look how this works. It is a well known and proven weather "saying" that drought begets drought and a wet pattern be gets more wet patterns. The reason that these "sayings" are valid hass to do with something called positive feedback. Large areas of dry grounds give off excessive Heat and lower than Normal Humidity especially during the hot Summer months. This additional heat feeds into the atmosphere and reinforces a ridge which might be in place at the jet stream level. Likewise large areas of really wet ground often mean that the soils are colder than normal and the excessive low level humidity from the wet soils feedback into the atmospere in such a way as to keep the mean trough position located over a general area.
These NEXT two images show the soil conditions moisture from last of all autumn-- NOV 7 2009 to be exact. The first image represents the LOMG TERM TREND ( the past few months) and the second image represents the SHORT TERM TREND or the past few weeks.
As you can see their large areas of extremely wet soil conditions covering all of the Midwest... From the Delta to the Great Lakes with a secondary area of wet conditions over the Northeast. There were also fairly dry conditions along the West Coast. The SHORT TERM TREND map showed that these are excessively wet soil conditions was continuing and if anything expanding into the deep south and the Delta .
My argument from last autumn was that the very cool Summer and sept and OCT of 2009 was just a precursor of the winter coming up. This was suggested / forecasted because of these very wet conditions which supported the mean trough being located over the Mississippi river valley . From that position any significant Low pressure area would come out of the Gulf of Mexico track up the East coast and bring large areas of heavy snow and Below Normal temperatures especially for the Northeast but for the Midwest in general .
As we know that is exactly what happened this past winter .
These images show the actual winter conditions (DJF) with respect to precipitation and temperatures. Notice that the Midwest east of the Mississippi River-- the ECB-- actually saw Drier than normal conditions while the East coast from Georgia to Maine experience wetter than normal conditions. With respect to temperatures ...the Northeast actually saw temperatures that were close to normal but to the West there were large area of Below and Much Below Normal temperatures across the Upper Plains and all of the Midwest into the Deep South .
That sort of temperature signature can only result from the mean trough position being located over the Mississippi Valley and the Midwest. The SOIL MOISTURE METHOD in a text book perfect manner!
Now let's take a look at the long-term and short-term trends with regard to the current soil moisture conditions across the CONUS.
This first image - LONG TERM TRENDS-- show that while the Midwest areas and the eastern Plains are still wetter than normal they are significantly drier than what we saw last November. The SHORT TERM TRENDS are even more impressive showing their large areas of the Great Lakes OH and KY are now drier and in some cases significantly drier than normal.
SUMMARY: the continuing drying trends over the Great Lakes and especially the ECB is additional proof that the overall pattern from the last year has come to an end. If this trend continues the dry conditions over the ECB could support the potential for a drought to develop late in the Summer of 2010 over the Midwest east the Mississippi River.
CAS CLIMATE MODEL
The CAS Model is the only climate model which actually uses the Soil Moisture conditions to forecast the next 3 to 4 months.
Research shows that the CAS climate Model is actually very good forecast four temperatures and moisture / rainfall for the next 30 days. Beyond that as is all climate models its reliability and accuracy rapidly weakens especially if further out and time you go.
However if you have areas of the excessively wet or dry conditions the CAS can be rather useful tool. In addition one of the good things about this climate forecasting tool is that it is updated every two days so that forecasters can actually track the trends of cold and warm dry and wet over several days and several weeks.
These first three images show the CAS model temperature and precipitation forecasts as of APRIL 14... valid for JUNE JULY AUG of 2010. As you look of these models you should notice that in none of the 3 months is the CAS forecasting wetter than normal conditions over the Midwest . In fact in June and in August the CAS is showing large areas of Below Normal precipitation over portions of the Midwest.
With respect to temperatures notice that the trend clearly shows that July and August will be significantly warmer relative to normal over the Midwest then June.
Looking longer term these 2 images are the CAS climate model forecast for three month increments... JJA- June July August... JAS= July August September and ASO = August September October.
Again what is Noticeable about these maps is that relative to Normal ... temperatures in the second half of the Summer and early Autumn of 2010 are clearly warmer than Normal. And with precipitation we can see large areas of Below Normal rainfall persistently located over the ECB.
It will be very interesting to follow the CAS Model as you move into may to see what changes if any a showing with regard to the summer months .
HURRICANE SEASON 2010.
In a word it is looking bad... REALLY bad with respect to overall TC activity. Those of you who get the energy and Hurricane forecasts from me know that since 2005 I have NOT been caught up in the media hype about forecasting another monster hurricane season like we s aw in 2004 and 2005. .
Indeed back in 2006 numerous private forecasters became caught up in a game of "I can top that forecast". They went extreme with the early season Hurricane forecast... whereas Wxrisk.com actually forecasted the lowest Tropical Cyclone activity in the Atlantic Basin of any of the well-known private forecast services. I remained bearish on hurricane activity throughout the 2007 and 2008 hurricane seasons as well even though in many of the private forecast services continue to over forecast the amount of tropical activity in the Atlantic Basin.
That Being said... over the past 30-45 days I have become awed by the extremely warm SSTA which have developed throughout the spring across the entire MDR (main development region) but especially over the central and eastern portions of the tropical Atlantic. These warm SSTA are far warmer than anything on new record easily exceeding the warm waters we saw in 2005.
In addition there is a strong correlation between Above Normal hurricane activity and moderate La Niņa events.. and between strongly negative QBO phases and Above Normal hurricane activity.
As long as the WIND shear is not too strong and the Saharan dust is not overpowering... It is very possible that the 2010 hurricane season could equal that of 2005 or perhaps even exceed it. It is way too early in the season to speculate about the amount of Sahara dust that will get into the far eastern tropical Atlantic or the shear across the Caribbean Basin and tropical Atlantic regions . If the Pattern does develop as I am forecasting the Ridge over the SE states will prevent Hurricanes from turning out to sea once they reach 65 west Longitude and steer systems into the Gulf of Mexico.
This is the Kind of pattern I expect for the 2010 Hurricane season: As you can see with the mean Ridge in the Jet stream in place over the Deep South I anticipate a trough in the Jet stream somewhere " downstream" ...in this case over the Central Atlantic ocean. This trough will at times be "deep" enough to cause early "re-curvature" of TC coming east.
In Addition the large mean ridge in the Jet stream over the Deep South will great REDUCE the threat of numerous Gulf of Mexico season. Thus besides the high likelihood of numerous TC in the Tropical Atlantic being turned out to sea early there will be a 2nd area of increase threat of TC activity NW Caribbean- Yucatan and sw Gulf (Bay of Campeche). One or two TC might reach far southern TX.