privately 2/24/08 ***
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.
The real forecast issue that meteorologists will have to deal with this Spring will be the condition of the La Niņa event by the time we reach MAY 2008. If the La Niņa event is still in the Strong criteria as we move into early Summer ... then the odds strongly favor a particular weather pattern. If on the other hand the La Niņa event is weakening we will end up with a significantly different weather pattern for the Summer months across the Plains and the Midwest. This is going to be the key issue in figuring the Summer forecast at 2008 and it is very important that energy and agricultural traders keep this in mind. The Summer 2008 forecast will be based upon a forecast or extrapolation of an event that is still several months down the road and that is always a risky proposition.
REVIEW OF WINTER 2007-08
The link below shows the WxRisk Winter 2007-08 forecast. If you would actually take a look at the forecasts and the Map issued with regard to the overall pattern you would see that the December and January forecast force quite accurate. However my February 2008 forecast was not nearly as good. This is mainly because I anticipated the La Niņa to weaken as ee moved into February. And I really did not happen so as a result the basic or fundamental assumption I had for the month turned out to be wrong. And not surprisingly so did the February forecast .
These next two maps show the overall pattern and I have highlighted the mean Jet stream position with a rather thick black line over the CONUS for the winter months of December January and February. Map#1 number one refers to the temperature pattern for DJF and as you can see temperatures were generally above normal over Texas the Delta the deep south into the Northeast US while over the western third of the US into portions of the Plains temperatures were below normal. This next Map shows the precipitation pattern we experienced during the winter months of December January and February. Again the superimposed thick black line shows the Mean Jet stream position and as you can clearly see the Great Basin region has been pretty wet along with a large area from of the central Plains into much of the Midwest and New England. However areas to the south of the Jet stream have for the most part been rather Dry this winter. That being said FEB 2008 has turned much wetter over the Deep South.
If we take a look at the Winter by region we can see that the precipitation patterns are clearly distinguishable over the central Plains into the Midwest. As you can see for most of the Winter the dark blues and purples show much Above Normal rainfall extending from eastern Colorado are across the central Plains and into the Midwest which is where the mean storm track was located.
With the temperatures we can see much of the same sort of thing. Again note how the coldest temperatures were located just to the north of where the Jet stream position was... over the central and upper Plains into the western Great Lakes. To the south and east of that we can see Above Normal temperatures across much of the lower Midwest and especially over the ECB.
As we prepare the Spring 2008 forecast we want to start paying attention to some of the trends we are seeing in February. There are numerous cases where the early Winter pattern is significantly different than what we see late in the Winter / early Spring and this can result Missing the pattern changes and thus your seasonal forecast often ends up in trouble. However in this particular Spring season the strong La Niņa event is still the dominating factor. And if we look at the temperatures for the month of February we will see essentially an unchanged pattern.
Over the Plains temperatures from the Rockies westward were quite mild but when we look at the eastern portions of the central and upper Plains temperatures during February 2008 were way below normal. This continued into much of the WCB region as well.
Precipitation for February 2008 can be seen here with very dry conditions over much of the central and upper Plains... but very wet conditions over almost all of the Midwest. This very distinct rainfall pattern between the Plains the Midwest occurs because the Jet stream has been so strong and powerful that these systems racing in from the West coast are developing their rain shields too far to the east to affect the Plains and as result.... the Midwest is getting slammed with heavy and rain and snow events.
The persistent nature of this weather pattern we seen over the central Plains and then into most of the Midwest has produced a large area of saturated ground that appears to be growing as the wet pattern continues into March. These two images show the trend rather clearly. First let's take a look at the short-term trends s with regard to droughts and rainfall. As you can see from the short-term trend Map much of the Midwest and the Northeast is now experiencing Much Above Normal with regard to soil moisture and saturation and many areas in Midwest are supersaturated. Also note the area of adequate or above normal soil moisture over the central Rockies. It should be pretty clear then that we can see where the mean storm track has been for much of the Winter running from Utah Colorado across the Plains into the Midwest and New England. Alston did he notice of the deep South region where are the extensive drought is shrinking rapidly as the one continues in the short-term.
The long-term soil moisture and drought Monitor trends which can be seen here This Map shows the lingering drought over the Deep South but it is not nearly as bad as it was Last Summer and Autumn. In addition the long term trends for Above and Much Above Normal rainfall over portions of the Midwest and the Northeast can be seen as well .
All seasonal forecasts regardless of whom or what companies actually make them... are all based upon certain critical assumptions which a meteorologist HAS to make in order to project the forecast for the next 90 or 180 days. Sometimes these are critical factors are overpowering and the forecast becomes relatively easy. This was the case this winter and the Summer of 2006. In the examples that were two or three overpowering the factors which really gone it to the entire weather pattern across the Western Hemisphere.
This particular winter which is now coming to a close the dominating factor was the strong La Niņa which actually exceeded most of forecast expectations made back in the Autumn of 2007. There NO computer forecasts or private forecasts that I know of which called for the La Nina to reach the "strong" intensity criteria for several weeks during the middle of this past Winter.
My particular winter forecast --again by referring to the link above called for a month or La Nina to dominate the weather pattern-- in the months of December and January but I anticipated the La Niņa to weaken during the month of February and early March. As a result my December and January forecasts were very good and quite accurate with the overall pattern temperatures and precipitation. However the February forecast was a disaster since it was premised on the idea of the moderately La Nina weakening which clearly did NOT happen!
There were some other factors of course besides the La Nina... such as the QBO and the Sea surface temperature anomaly patterns in the North Atlantic Ocean which were hostile towards the idea of any sort of sustained blocking patterns developing over Greenland or Eastern Canada.
As we move into the Spring 2008 forecast (and then take an early look at the Summer 2008 forecast) we can see that the La Niņa is going to be the dominating factor once again. The reason for this is that there is a significant difference in the historical climatology between a strong / Moderate La Nina versus a Weak La Nina. Thus ANY forecast that is premised on the idea of a strong / moderate La Nina continuing thru the Spring and into the middle portions of the Summer.... HAS to reflect the conditions we see during Spring and Summer months of a strong or moderate La Nina. On the other hand if you are forecasting a Moderate La Niņa for the Spring with a weakening La Niņa during the Summer months (the DTN forecast) then your forecast is going to be significantly different because the patterns we expect with a weakening La Niņa during the Spring and Summer months is different.
WHAT ARE THE SPRING TIME CONDITIONS MODERATE / STRONG LA NINA EVENTS BRING TO THE CONUS?
These Next two images come from the climate prediction Center ( CPC) ENSO diagnostic discussion web page. The first map shows three different maps which all representative of the the typical precipitation patterns the CONUS experiences in La Nina events. the top map represents the areas of above normal and the little normal rainfall with weak La Niņa events... no matter presents moderate lightning events and the bottom map represents the top of rainfall patterns we see with strong La Nina events. one thing that you'll notice is that regardless of the type of La Nina event the spring season seems to favor an area of much below normal rainfall over the western corn belt / upper Mississippi Valley which extends into the eastern portion of the Plains.
This next image refers to the temperature patterns we see during the Spring season with weak Moderate and Strong La Nina events. The Top map ...weak La Nina -- shows very little correlation between any sort of temperature anomalies over the Plains or the Midwest but there is a tendency for the Pacific Northwest to run somewhat below normal. In the moderate and strong winning events we can see a large area of below normal temperatures over the Pacific Northwest and northern Rockies and into the far upper portions of the Plains near the Canadian border. On the other hand there is a large area of Above and Much Above Normal temperatures that extend from eastern Texas of the Delta and the entire Deep South.
Now that we know what the typical La Niņa spring time patterns with regard to temperature and precipitation typically look like... the next issue is to determine what sort of La Nina event will the CONUS and southern Canada see this Spring and possibly into the Summer of 2008?
This next map is presented so
that the reader can more easily
comprehend that La
As of March 1 the La Nina event in region 3.4 reached its peak of nearly -1.90c in the first two weeks of FEB. Since them the La Nina has showed very slow warming.
HISTORY OF SHORT
La NINA EVENTS ( weak) vs
this next table -- called the ONI index-- comes from the Climate Prediction Center --and it shows a history of all the La Niņa and El Niņo events in the critical ENSO region of 3.4 since 1950. I have highlighted two different types of La Nina events. The YELLOW shading highlights the long lasting La Nina events while the AQUA BLUE shading highlights the short duration La Nina events.
By highlighting the history of all the La Nina events since 1950 it should be readily apparent that in the yellow shaded / LONG lasting La Nina events the sea surface temperature anomalies in ENSO region 3.4 reached or exceeded -1.5c while in the short duration La Niņa events the sea surface temperature anomalies did NOT reach -1.5c
CRITICAL POINT: they' have been 4 long-lasting La Nina events since 1950. In every instance the sea surface temperature anomaly dropped to -1.5c or lower and the total event lasted 27 to 36 months.
In the 4 of the 5 short duration La Nina events Sea Surface temperature anomalies never exceeded -1.5c ...except in the 1988-89 La Nina event. they are for the odds and the climate history of logging events strongly indicate that the current La Niņa event will continue for at least the rest of 2008 possibly into early 2009. The CURRENT La Nina event may not have the same intensity as it has right now but the climate history of La Nina events is very clear -- this La Nina event still has a long way to go
THUS the analog years we need to focus on -- the YELLOW SHADED events-- are the Spring/ Summer season 1949 1950 ... 1954 1955 1956.... 1973 1974 1975... 1999 and 2000.
Some forecast services -- such as DTN's Bryce Anderson / Mike Palmerino and INFORMA's Rick Shields also consider the following La Nina events to be analog events ...1988-89... 1970-71... and 1964-65. But as I proved from the data above those events were SHORT duration La Nina events and did not see the ENSO Region 3.4 seas surface temperature anomalies drop to -1.6c to -1.9c .
This is what MARCH Temperatures and Precipitation patterns looked like for the CONUS in the analog years of 1949 1950 ... 1954 1955 1956.... 1973 1974 1975... 1999 and 2000. As you can see Temperatures MARCH of these analog years featured a marked contrast with Much below Normal temps over the Pacific NW into the Upper Plains/ south central Canada... while southwest states southern TX and the Gulf coast had Above and Much Above Normal Temperatures.
Rainfall in these Analog La Nina Spring years featured somewhat wetter than Normal over the Delta the Southeast into the Lower Midwest and into WVA and VA as well as the Upper Plains and Pacific NW. DRY conditions over the central Plains into the SW states.
This is what APRIL Temperatures and Precipitation patterns looked like for the CONUS in the analog years of 949 1950 ... 1954 1955 1956.... 1973 1974 1975... 1999 and 2000.
As you can see Temperatures APRIL of these analog years featured still featured a LARGE area of Below and Much Below Normal over ALL of the Western third of the Conus as well as all of the Upper Plains and south central Canada... and into the Most of the Midwest.
Rainfall in these Analog La Nina MARCH years featured somewhat a large area of Drier than Normal over the Southwest into the central and Lower Plains... and drying trend over the Deep South NW.
This is what MAY Temperatures and Precipitation patterns looked like for the CONUS in the analog years of 949 1950 ... 1954 1955 1956.... 1973 1974 1975... 1999 and 2000.
in addition to the actual climatological history of the lending of
events since 1950 weather forecasters can have access to various
computer models which specialize just in forecasting La Niņa and El Niņo
events. This latest projection which comes from the IRI --
international research Institute-- is a composite of over 20
various computer models. As you can see most of the computer models show
La Niņa weakening as we moved into the Summer but they
do keep the La Nina event going right
of course the trick is not to rely too heavily on any of the computer models when you're dealing with long-range seasonal forecasting because sometimes it can have very strange solutions. One of the ways of getting around that is to view the recent climate computer models and see if they have been any good over the past few months. For example here is the GSM climate model forecasts from January 2008 with regard to the precipitation for the next three months -- FEB- MARCH- APRIL.
The GSM for the Spring 2008 season is predicting the
following... this map shows the overall Jet stream pattern which I have
superimposed with the black thick lines... we can see the mean Trough
position is centered over the Rockies and Plains states which is
basically a continuation of the pattern we have seen this past winter.
Not surprisingly the temperature forecast from the GSM for March
April May reflects the overall jet stream pattered with a little normal
temperatures over much of the Pacific Northwest the West Coast
south-central Canada and into much of the Plains and WCB...
IF THE LA NINA HOLDS AT MODERATE / STRONG INTENSITY THJU SUMMER OF 2008