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johnholmes

Some Information About Teleconnections

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Teleconnections and LRF work

I am very much a learner in this field even for the time scale I have attempted over the past 3 years. That is beyond 10 days out to about 25. There are several on Net Weather who have much more experience than me. Beyond 25-30 days and much of what I read, well the reasons given for particular weather patterns being predicted, is even more of a mystery-much learning still to be done.

Taking short term forecasting first. The Met Office show, and NOAA data for the northern hemisphere 500mb flows does support this, that out to about 6 days (T+144), sometimes less, the accuracy is between 80-85%. Nothing approaching this, in my view, is possible OVER A PERIOD OF TIME for lrf forecasts, although isolated cases do show stunning accuracy at times. For lrf work. Over a 3 year period of doing 10-25 day outlooks I found I was ‘correct’ in the early part of the period(10 days) about 70-75% of the time falling to an average of around 60% by the end. So longer term forecasting is a possible fruitful area on this time scale. Longer term, a season or 3 months ahead, also seems to be showing promising results from a few people.

When doing forecasts beyond about T+144 (6 days) using just the ‘synoptic’ models becomes fairly chancy in my opinion. Models like GFS do have some stunning correct forecasts but overall the number correct is probably, no actual data to support this other than 5 years watching and working with the models, of well under 60%. So the use of what are termed ‘teleconnections’ for the short term lrf work with the synoptic model will almost always give better results. Well in my view it does!

Remember that any forecast of persistence works out with an accuracy of about 30+% I believe, be it a day ahead, a week, a month etc.

What are TELECONNECTIONS? One as good as any is from the official weather forecasting in USA for all ranges is given below.

Teleconnection - A strong statistical relationship between weather in different parts of the globe. For example, there appears to be a teleconnection between the tropics and North America during El Niño.

Equally their explanation of why forecasters use this method rather than others is also well put.

Long-range forecasters sometimes look to the past to predict the future. Yes, you read that correctly. To do this, forecasters rely on a technique called analog forecasting. Analog comes from the word “analogy,†which means “likeness†or similarity. Here's how it works. Meteorologists first determine the average positions of the long-wave troughs and ridges in the jet stream during the weeks and months leading up to the present. Then they look for previous years during which a similar pattern occurred during the same season. Stated simply, they look for “analogs.†Forecasters then follow the evolution of the upper-air flow during those analog years, note the evolution of the general temperature and precipitation patterns, and then incorporate these patterns into their seasonal outlooks.

Analog forecasting has been around for decades, but it’s utility for monthly and seasonal forecasting has increased in recent years. That's almost entirely a result of our evolving understanding of teleconnections. El Niño and La Niña are two of the “biggie†teleconnections that have proven useful for forecasting on times scales of months and seasons

During this information on LRF work there will be much use made of acronyms, a good place to start for them is within Net Wx at

http://forum.netweat...weather-guides/

Go to the relevant heading, there are at least two that will help.

So using these teleconnections is one of the main tools a forecaster uses in trying to predict general weather patterns beyond about 10-15 days. Even before that time scale, the use of them with the basic synoptic type model output will usually yield a better and more consistent forecast than the use of the synoptic model alone.

The teleconnections are available in a variety of ways and have validity over differing time scales. The lower end are really outputs like the synoptic model but with other factors included. Thus the 500mb anomaly charts issued by GFS and ECMWF as well as NOAA fit this bill. Forecasts out to 10 days, the mix of model and TC (teleconnection) is an example of this. Further out are AO, NAO, PNA (remember the acronym list link?), with other teleconnections clicking in, terms you will see used are ENSO, La-Nina, El-Nino, MJO, QBO,GWO, Stratospheric temperatures and wind profiles, out to the sun. The sun being the driver of the earth anyway but with a very far from well understood part to play in seasonal forecasting for instance. All those mentioned are used, the later in the list then the further out in terms of days ahead you are trying to predict for. Some charts using some of these TC’s are also produced, on Net Wx you can find in Extra the raw CFS output run most days and the Long Range Forecast maps. The latter is another output from USA, done once a week and going out to 9 months. There are others like that from NWS/NCEP another NOAA output. These charts seem to often figure in many ideas of what the winter in particular will bring. Even UK Met uses them. There are many more TC’s but there is enough already to keep you going understanding them for now! But one other must be mentioned as it is probably just about the most important single one for seasonal and even on 15 day upwards. That is the anomaly of Sea Surface Temperatures (SST’s). Water heats and cools at a markedly slower rate than land masses. Thus the interaction between the oceans and land, as well as the heat exchanges occurring beneath the surface are vital. It is only relatively recently that meteorologists and climatologists (in comparison to surface temperature overland) began to compile data and try to use SST’s as part of forecasting; so much to improve in that in my view. SST’s are the driver for La-Nina and El-Nino which in turn are major players in subsequent seasons down the line.

So to return to my lrf length and which TC’s I use.

First how detailed can we be beyond say 10-15 days, indeed from about 10 days? The answer, in spite of what some people may believe, is only a general idea of the weather type. Warm/cold/wet/dry/windy/notwindy etc in comparison to the averages. Even with averages you will see people on weather forums arguing over which average should be used but provided a poster states what the averages are they are using, in my view, it matters not one jot. If the actual one being used is quoted or referred to its easy enough for you to covert it to the one you prefer!

The first time scale is 10 days upwards and for this I use a mix of 500mb anomaly charts and the outputs from ECMWF and GFS mainly. Beyond this then we really are into the TC area. First in time from T+00 are AO, NAO, PNA (see link given above as to what they mean and explanations) These can often help, along with other TC’s being place in determining whether we are likely to see a disturbed Atlantic type of weather, whatever the season although all 3 are more consistent in their help in the winter months. Negative values for AO and NAO usually, a favourite word with meteorologists as there are almost certainly going to be exceptions, show a less mobile Atlantic. This tends to favour cold outbreaks and some guidance on where the build of upper ridges with their surface highs beneath are most likely to form. Other TC’s can help to suggest more accurately where these might be. The upper flow becomes buckled or, to quote the technical term, meridional rather than chiefly zonal.

For longer lrf work then TC’s such as ENSO (La-Nina or El-Nino weather patterns), AGW, GWO, QBO, in my case 30 mb temperature levels, more accurately, winds and temperature profiles in the Stratosphere, and obviously out to the sun. Just how much part that plays in seasonal forecasting is the subject of, at times, quite heated argument. A ‘quiet’ sun as opposed to an active one does appear to tend to hold down if not decease global surface temperatures with the obvious knock on effect for both water and land, in terms of months and years.

I think that is probably enough for any newcomer to this topic to be going on with but its far from an exhaustive list. Search Net Wx for more and try Google which will come up with hundreds of links to LRF and seasonal forecasting.

I hope it helps. If you disagree with anything I’ve posted please post why and any suggestion as to how to correct it.

The next entry will be in pdf format and is really trying to illustrate how forecasting of any length ahead, but in this case 10 day upwards, is just as liable for changes from the guidance used as are short term forecasts.

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Thanks John - really useful information. I will come back to it in the morning when my brain has recovered a little from a heavy week at work! I suspect that these sorts of patterns, whilst being difficult to understand and interpret, provide the missing link for serious forecasters (unlike myself) between seasonal patterns and the shorter term predictions. I also don't buy into the 'chaotic' system view - I just think we don't have enough inputs, and processors powerful enough, to produce accurate forecasts..... yet. 

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That's a fascinating read, thank you John

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Your imput on this is appreciated John.

I too am trying to get some basic understanding of the TC`s and like many on here avidly read the posts by yourself,GP,Chion.and others .

I feel there is so much to learn other than understanding the basic sypnotics and contributions from the more knowlegable members are always gratefully received.

I look forward to your next installment John.

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Thanks JH this is my interest and really good to get more people into lrf i think, im only starting out on TCs and LRF myself, have learnt alot from GP/TWS yourself and others ,also from Nick.f on storms, look fwd to further learning. its great when we can understand what were looking at on the screen and how to use it!

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