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I hope by now many have realized the folly of making early winter season forecasts are especially atmospheric and oceanic conditions which are undergoing significant changes. As I argued in the Preliminary Winter forecast the early forecasts for the Winter of 2009 -- 10 have been based on a several faulty assumptions in a manner very similar to the Winter forecast debacle of 2005 -- 06 after the historic hurricane season of the summer / autumn of 2005. In this case however it has not been hurricane season but it has been these assumption that specific atmospheric events will hold or develop as he moved into the winter.
The first one of these has been the assumption that the El Nino would stay "weak". That clearly has not been the case and nobody is disputing this anymore. I wish some would have realized the potential for the El Niņo to rapidly develop in November when they made their overhyped extreme winter forecasts back in September and October. The impact of the rapid rise of the El Nino into the upper levels of the Moderate category over the last few weeks clearly affects a lot of Winter forecasts... mine included. My initial or preliminary Winter forecast featured a large areas of Below and Much Below Normal temperatures over the Plains and Midwest. Clearly that is not going to be the case especially in the first month or 45 days of the winter ( DEC).
The other the argument that was made is that the PDO would run positive as We moved into the winter months ... with the argument being that as we moved into November and towards December sea surface temperature configurations would move shift to one that shows a sustained +PDO.
FINAL WINTER FORECAST 2009-10
MAPS ISSUED IN THE MID OCT FORECAST
As you can see I have made substantial changes.... in my winter forecast and ideas since Mid OCT.
THE PDO ISSUE
Clearly that has NOT been the case however the issue in this matter has NOT yet been decided. The latest PDO values have started to drop and this is reflected in the early November PDO values from Washington state and ERSL. In addition the constant stream of systems moving across the Northern Pacific and Into the Alaskan Panhandle and western Canada has been causing upwelling which is not allowing for any sustained warm SSTA to develop off the west coast of US/ Canada. That being said I must admit that it would not take much for the sea surface temperature configuration to shift into a +PDO.
There is a large pool of relatively colder than normal water over the north-south Pacific and a fairly sustained warm pool of sea surface temperatures in the central Pacific. If we can get the warm water to extend towards the West coast ...IF ....this would establish the classic "Banana" or "U shaped" desired sea surface temperature configuration of a +PDO.
All that being said it should be noted that for the second half the winter I am actually pretty bullish with respect to colder than normal temperatures and the potential for significant winter storms east the Mississippi River and this includes a higher than normal threat for significant coastal storms as well. Once the moderate El Niņo begins to break down... which I am assuming with some basis in fact... will occur late December or early January... the overall pattern for the central and eastern US could be at times pretty cold and rather stormy.
Again let me emphasize that this forecast is assuming that the El Niņo breakdown during Mid or late December or very early January. There is a real possibility might not break down until much later.
THE ENHANCED PACIFIC JET / +EPO
Another factor which I detected in Autumn ..which was generally ignored by other forecasters... was the development of the powerful Pacific Jet and consistent stream of energy moving across the northern Pacific into the West coast of North America. The enhanced Pacific jet is being caused by a persistent strong negative height anomaly over the Aleutian Islands and the Gulf of Alaska ... the +EPO .... which has seen a series of massive storms... some as deep as 945 mb-- move into that ares then track into either eastern Alaska the Alaskan panhandle and/or Western Canada.... and a positive hide anomaly over the southern portions of the northern Pacific. These two features have acted as a " funnel" for valve which helped create the enhanced Pacific jet.
This sort configuration is very common during a moderate El Niņo especially in the first half of the cold season months.
THE EL NINO OF 2009-10
Clearly for many forecasters this has been the biggest surprise over the last 30 days. It is hard to overemphasize how common and how critical the assumption was that the El Niņo would stay weak for the winter of 2009 -- 10 and not strengthen appreciably. WRONG. And that includes my preliminary Winter forecast. I do give my self SOME credit in discussing this critical assumption in MY preliminary winter forecast . This chart clearly shows the significant warming which has occurred all areas of the ENSO regions over the past several weeks. The latest data from CPC and the Aussies shows that we are seeing some leveling off of the El Nino so I don't think we will be looking at an event which is going to reach +2.0c (which are placed El Niņo in the strong category) . As we can see from these two images 10/26 and 11/16... there is a huge pool of very warm water below the surface which appears to be migrating eastward towards the Peru coast.
As this massive bubble of warm SSTA propagates eastward waters cool off significantly behind it. Whether or not this becomes a persistent trend is something that will have to followed during the early portion of the winter.
Since 1950 there been several El Niņo events which have seen significant rises during late October into November. In some of these instances this warming has continued into early and Mid December or beyond with the El Niņo SSTA often reaching +2.0 temperatures. As I stated above it looks like that this is NOT going to be the case as most of the El Niņo models show the event leveling off and then beginning to weaken at a pretty steady pace in the second half the winter moving into the spring.
As you can see from the conglomeration of El Niņo forecast models from IRI and the European folks... there is a strong inclination to believe that this current El Niņo will weaken. The question then becomes when does the El Niņo weaken? Mid or late December? Early January? March?
There seems to be a general consensus that this current El Niņo will weaken for the second half the winter significantly and right now I am inclined to agree with that. But again I urge some caution here because it was only a few weeks ago that we all assume that the El Niņo stay weak and would not strengthen.
OCT CFS shows a 2nd PEAK in early January and the 16 NOV CFS seems to be holding onto that idea.
Going on that assumption.... I can find FOUR Winters where we had El Niņo events which rapidly strengthened in late October and November only to weaken during late December/ early January. Those winters were 1965 -- 66 2002-03 2004-05 and 2006 -07. In all four of these cases we saw a mild and or very mild Decembers.... followed by a significant shift in the overall pattern at some point during the second half of winter. The best-known and most recent case of this was the El Niņo event of 2006 -- 07. This featured a very warm December over the entire nation east of the Rockies followed by a rapid breakdown of the El Niņo during the holidays... and then massive pattern shift to a significant cold of the normal regime especially east of the Mississippi River... from January 15 of March 15. That 60 day period was one of the coolest 60 day periods ever seen in CONUS in the last 100 years.
Of the four Winters I am considering ...the 2004 2005 winter is the least of the favorites and weakest of the analogues since the El Niņo in that event was based in region 1+2 and that is not the case with the current El Nino.
This is a very impressive development over the last few weeks. The snow cover which started off with much below normal over Eurasia has not only reach normal levels but is now Much Above Normal!!. At the end of October the snow cover in Eurasia came in at the 10th best snow cover on record and I am sure at this point the snow cover over Eurasia is still Much Above Normal even for the middle of November. Not surprisingly a very intense and large Polar Vortex has developed over Siberia which has allowed for several significant /severe cold air outbreaks to occur into central and northern China along with several major Low pressure systems.
On the other hand to snow cover along the border regions of Canada and the United States is actually little below normal because the mild conditions.
The issue then becomes one where the pattern allows for the heart of the Arctic air to shift from Siberia and Eurasia over into the Western Hemisphere at some point during the winter months. I believe that shift will occur in the second half the winter as the El Niņo event breaks down.
However the new data showed that the QBO did not drop but in fact actually rose a little bit... and plotting the daily QBO values shows
the QBO holding steady. This I believe is actually favorable for saying the same blocking patterns especially in the second half the winter.
SOIL MOISTURE ISSUE
the latest trends in long-term and short-term soil moisture maps shows some subtle but important differences developing. The main difference is that in the short term the maps have turned significantly wetter over the Delta and portions of the Deep South and has stay just as wet over the Midwest and the Mississippi River Valley.
Although my argument was greeted with some skepticism indifferently logical circles and communities more and more folks are beginning to realize that the soil moisture issue seems to have an impact. Already since the middle of October we have seen several significant systems over the Plains and Midwest and a persistent track through the Plains toward the Delta up into the Great Lakes.
Indeed in each medium range and extended forecasts as of November 16 we can see several more systems coming out of the Pacific jet amplifying over the Mississippi Valley and tracking up to the Great Lakes and/or the Midwest.
This is telling me that the meaningful trough position is likely to stay over the Mississippi Valley for a good portion of the winter. When the Pacific jet is accommodating a pattern this will result in the East Coast saying above normal temperatures- except perhaps for northern New England. The Midwest states during the warm periods will probably stay seasonal Mild and wet... while the Plains states are likely to see temperatures way above normal.
However once the pattern shifts... having to mean trough position over the Mississippi Valley can be extremely positive if one is looking for cold and snowy conditions over the eastern US and especially over the Northeast. Not only do with this support having a mean trough centered over the eastern third of the nation but it is a hard fast written rule that for significant Northeast snowstorms it is ideal to have the long wave trough position neutrally aligned over the Mississippi Valley.
That being said of course a lot depends on the down stream 500 MB features... one can have the most perfectly aligned Long wave trough centered over the Mississippi Valley with a neutral tilt but if you did not have the proper downstream pattern you will end up with a Ohio Valley... or Appalachian... or in land runner type of coastal storm .
But right now I do view in the general sense the increase moisture and storming us over the Delta region as a potentially positive effect for the second half the winter for the eastern third of the Conus.
THE CAS MODEL
Lastly let me mention briefly the CSA Model. When you have a active wet pattern like the one we have been experiencing for the last several months the CAS Model can be a useful tool to gain you some insight as to what the next few months are going to be like. On the other hand if you are seeing a pattern which is not showing a strong signal towards excessive wetness or drought ...than they CAS model is usually a piece of crap .
The December CAS model is showing actually fairly warm conditions over much of the nation with the heart of the warmth located over the Plains and upper Mississippi Valley and the Rockies. In general this matches the analog years that I have selected .
The January map actually shows a pattern reversal with the coldest temperatures almost over the same locations that see the warmer temperatures in December!! ( Plains upper Mississippi Valley and the Rockies ). The Northeast -- New England and the middle Atlantic states see near normal temperatures... and note the still active wet pattern over the Deep South.
And finally in February notice that much of the nation north of Interstate 80 is fairly cold... and there is an excessively wet pattern shaping up running from the Tennessee Valley into the middle Atlantic states.... which if your snow lover living in these areas could make your day is not for winter.
In the overall sense that is NOT a bad forecast. Again let me reiterate the point that I am not in love or endorsing the CAS model. But during times of excessively wet patterns like we are seeing over the Plains and Midwest into the deep South or during times of excessively dry patterns the CAS does not always suck.