Presented by : Matt Strouse
Real Wx Services
Created: 10/11/2010
The winter of 2010-2011 is right around the corner and as usual there is a lot of talk going around the internet and also a lot of different forecasts and opinions as well. As is the case with any long range forecasting there are a ton of variables that come into and under consideration besides just the ENSO status. So what this is an attempt to do is look at all the different variables that come into consideration as well as a look at what has been happening and potentially could happen in regards to the winter of 2010-2011.
I will state right from the beginning that confidence in this years winter forecast is low to medium at best due to the nature of the ENSO status approaching uncharted territories.
The first thing that we wanted to notice is that the MEI or Multivariate ENSO Index is at levels that has not been seen since 1975-1976. This is what that particular winter looked like.
Another Oscillation Index that needs to be taken into consideration is the North Atlantic Oscillation. When we look back to the 1975-1976 winter we see that the NAO was essentially neutral negative that rose more positive in the last part of winter. The importance of the North Atlantic Oscillation is that when it is negative there is High pressure over Greenland and the downstream effects into the Eastern USA is to have colder air and potentially a trough across the region. However, there is a major difference between the NAO now and the NAO back in our potential Analog year.
Still yet another Oscillation to take into consideration is the Pacific North American Oscillation. This is an important index as well for when it is in its positive state it generally shows a trough along the east coast and a ridge along the west coast in which usually implies colder air in the east and warmer in the west.
As you can see there again is a substantial difference between 1975-76 and the current time frame as in the case with the NAO…the PNA is also opposite of what it was during 75-76. As opposed to being negative it has been positive since 2009 as well.
Next oscillation that has a large hand in contributing to the winter weather and weather in general is the Arctic Oscillation or the AO. This is important because when you have a negative AO it forces the jet stream further to the south and generally supports an influx of colder air into the eastern USA… and when we look at this teleconnection historically we find it also stands opposite and in stark contrast to 1975-76 when the MEI was at the same levels as 2010 is.
So when one looks at the above teleconnections in there current state thru September of 2010 this would create a very positive outlook for the winter of 2010-2011 because a Negative NAO , Negative AO, Positive PNA would all lead to a very cold winter across the Northern Half of the USA and the Northeast. It would stand in complete contrast to what 75-76 winter shows above and you can see the reasons why . Teleconnections are very important when it comes to long range forecasting and even the shorter term weather.
In addition to these connections above there is also the QBO which is the Quasi Benniel Oscillation. The QBO which was negative and deeply negative has switched camps and has gone positive and currently is + 6.58. This generally is not very good for winters…however…one of the Analogs had a positive QBO and that was 75-76 winter. So I am not sure how much of an effect this is going to have on the winter at this point. Some times a positive QBO during the winter with a La Nina can lead to a warm winter nationwide.
However… there are more things we need to address and look into before we can even begin to put across the forecast for this winter.
Another aspect that we like to look at is the SST’s along the east coast.
This is important as seasonal variations now start to play a key role, as during the winter and springtime, this belt of cold water sets up a strong temperature gradient with the warmer water to the south, resulting in a strong baroclinic zone along the gradient which pulls the subtropical jetstream to the south, creating a positive feedback with the negative NAO. This has favored lower-than-normal pressures in the northeast Atlantic during the winter and spring months. Its quite possible that this will play an important role in winter 2010-2011.
Still yet another thing that has to be taken into consideration is the Northern Hemisphere Snow Cover.
Something new that we are looking into this winter season is the relationship between an active hurricane season and winter. Is there any correlation between the two occurrences?
While we currently stand at 16 named storms with the recent birth of Paula ..we are going to look at a list of the top ten named seasons for cyclones and then look at the following winter. I am not going to include seasons with 21 storms or higher because I do not believe that is going to be obtainable but we will look at seasons with 19 Max and 15 min as that is the range covered in the top ten outside two years above.
That list is as follows:
1995 -19 storms
1887 -19 storms
1969 -18 storms
2008 - 16 storms
2003 -16 storms
1936 -16 storms
2007 - 15 storms
2004 -15 storms
2001 -15 storms
2000- 15 storms
Now we will look at the following winters:
In order to be considered since this Winter Season will be a La Nina we will only include them if they were La Nina.
1996
2001
So when we look at the only four years that were La Nina winters following 4 of the top ten hurricane seasons with named storms we find that we also while in a La Nina winter have a cold out look across much of the nation. Now whether this has any type of correlation to winter or not it is indeed quite interesting and something that is being factored into the equation.
So thus far what we are looking at is recent past weather history since 2009 has been showing a rather + PNA, -NAO and -AO ..with snow cover in the Northern Hemisphere at normal to slightly above and 4 of the top 10 hurricane seasons as far as named storms all pointing to a winter that would be pretty much normal to colder then normal across much of the USA.
However…a look at this past summer shows that we had to contend with a strong SE ridge.
This created some very hot weather across the eastern USA . Do any of the other years look anywhere close to this past summer? 1995 was pretty close.
No two analog years are ever going to be quite complete or identical because each season despite teleconnections being similar the weather patterns can be different. The summer of 2010 featured a stronger SE ridge then what the summer of 1995 consisted of. So this brings us to look at the weather patterns that seem to be developing as of late as the final factor in deciding the potential outlook for the winter of 2010-2011.
In the first 120 hours of the global guidance we see a pretty potent NorEaster that could be effecting the Northern Mid Atlantic and the Northeast. In the latter part of the run we see another pretty potent storm but this one stays off the coast at this point a good distance. So while September was a month with mainly warmth and zonal flow ..October is starting to take on the appearance of the trough along the east coast and ridge out west..
So with all the above discussed it is basically time to throw the pieces of the winter puzzle together.
The winter of 2010-2011 should feature a mainly negative NAO though from time to times it will fluctuate to the positive side. When it fluctuates to the positive side we will experience times of warmer weather . I think this will fall around mid January to mid February as to when we could experience the positive NAO and January thaw! With the pattern seeming to pretty much be switching gears to potential Noreasters it leads me to the conclusion that winter may actually start early across the North and the northern mid atlantic and that parts of the NE may see flakes in the month of October yet as well. Winter could come in fast and furious in the month of November leaving a very cold December in its wake.
I also feel that the PNA should also remain relatively positive ..though at times it also may go negative and we would experience that warmth. The PDO will remain pretty much on the negative side and like explained earlier that normally means that the jet stream would be further to the north but this year we have the Atlantic Tripole effect and I think this will end up being a wild card and will help to pull the colder air further south then what would be normal with a negative PDO. This would be because of the effect of the NAO as explained also up above.
If one were to use Analogs as there years it would essentially be a combination of 1975-76 winter and the year of 1995-1996. So with all the above in mind… this is the Real Wx Services 2010-2011 outlook for across the USA.. Verification will be done after winter is over…
Precipitation
