-2.86 on the 6z - a stonker!

-3.26 after 12z and these forecasts are coming towards months end now of course.

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Tim I agree that a correlation coefficient of r=0.91 is incredibly(if not suspiciously high).The AO is linked to the NAO though i,m bot sure how strong the link is. The NAO  DJF CET correlation is around 0..6 ie it explains c 40% of the winter temperature variability.So even if the 0.9 is correct some statistics about  the further link between AO and DJF CET are required before we get too excited.

OPI = -3.36 on the 00z this morning.

Let's look at a most extreme-case scenario, where the figure for the next 10 days of the GFS is -4.0. (In reality it must be higher).

Let "n" be the average OPI for each of the 16 days of October for which we have actual, banked data.

((-4.0 x 10) + 16n)) / 26 = -3.36

So, -40 + 16n = 26 x -3.36

So, 16n = -87.36 + 40

So, n = -47.36 / 16

So, n = -2.96

Shocked smiley.

Which means that with over half the month gone, the OPI has already shown an unchangeable, actual, non-GFS figure of -2.96. And that's with the 00z GFS being insanely blocked, which it isn't. In reality the figure will be lower than than -3.0.

Even more shocked smiley.

Bear in mind that with a negative QBO (as we have this year), any figure below -1.5 suggests a negative Arctic Oscillation for all three winter months.

Very exciting.

(Disclaimer: A level maths grade C 1978; it's a very long time ago and I would be grateful if someone younger could check that I've formulated the algebra correctly.)

@Roger: At The Other Place Murr has suggested that a positive QBO is the reason why negative OPIs haven't corresponded with cold UK winters in certain years.

I know that you have found that the QBO in general hasn't shown as much correspondence with cold or mild UK winters as some people imagine, but perhaps in combination with this kind of atmospheric set-up, there is a more robust connection

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Sorry it's all beyond me, LOL!

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Gavin P: I worked as a teacher once many years ago. If I had a quid for every time I've heard those words ...

Just focus on that OPI figure of <-2.96 from the first 16 days of October. That is going to take a hell of a lot of shifting upwards in the remaining 15 days for it to become positive.

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I wonder what the index was last year?  Mind you a negative AO doesn't necessarily equate to cold over the UK but it increases the chances of it.

Pretty interesting though, I do believe there is an element of persistance which begins to show in late Autumn (i.e blocking over Greenland, SSTs) so it will be interesting to see what happens.

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Riccardo published a value of +1.6 for October 2013 on 7th November 2013 - see link below

http://www.americanwx.com/bb/index.php/topic/41639-seasonal-winter-20132014-forecast-based-on-opi-index/

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Still in negative territory based on yesterday's GFS12z run.

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Given we're under the final ten day's of October and every day this month has been negative, surely the only question now is HOW negative will be the OPI be this October?

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On the face of it this morning's runs look promising enough, with GFS showing the deep low pressure tracking from NW of the UK to Scandinavia not quite managing to merge with further deep low pressure from the other side of the hemisphere, so preventing the development of a more organised polar vortex.

ECM does a better job than GFS, but of course it's output isn't used so we can only imagine what sort of values the ECM run would produce.

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Yep - pretty sure I read that if we had neutral OPI values for the rest of the month we would still finish lower than -1.

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My understanding is that the calculation is based on geopotential height anomalies across the Pole on the line from Canada to Siberia, i.e. horizontally on the projection below:

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=228&mode=12&carte=1

 

This is the 06z GFS for the very last day of October, and weakly positive anomalies are still clearly visible exactly along the Canada/Siberia Polar axis, which is what we need for the OPI to remain negative.

I know this is a hobby horse of mine, but the word "anomalies" is important. Weak low pressure across the Pole would still generate a red-coloured positive anomaly at the end of October, the time when you would normally expect the Polar vortex to be assembling. 

So don't assume that the sight of low pressure over the Pole would necessarily imply problems for maintaining a negative OPI.

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Something interesting I've noticed regarding the entire list of OPI recorded years, is that the lower the figure is, the more frequent are the cold incursions during the Winter period, as well as a higher risk of a more sustained and intense cold spell during the Winter.  

And it seems to me that a positive OPI doesn't guarantee that there won't be a severe spell the following Winter, as is shown by the positive 1990 figure.

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You can see how it happened here, Andy:
http://www.meteociel.fr/modeles/archives/archives.php?day=8&month=2&year=1991&hour=0&map=5&mode=0
A positive Arctic Oscillation with low pressure over the Pole, just as the OPI for Oct. 1990 suggested. But the Russian high marched westwards into Scandinavia underneath it.

The odd thing is that the Quasi Biennial Oscillation appeared to be in its positive phase at that time, which just goes to show, it's a funny old game, eh?

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I'm fairly sure it was mentioned on here last winter that the QBO was in a positive phase throughout that season. Indeed, this was sited by a few people as being one of the reasons why last winter was so poor from the point of view of those seeking cold weather.

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This looks a strong indicator for the AO. I can't help wondering whether some refinement may improve it further. the chances of the most indicative period being exactly 1 month long and exactly matching with October must be quite slim, perhaps there is some mileage in looking at whether the relationship with AO improves further by including the last week of September, or the First week of November, or excluding the first week of October, etc... if you get my drift.

However seeing as the figure looks like being negative this year, I am hoping it is accurate again this year as I am hoping for a bit of snow!

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Must admit to being pretty skeptical about this

 

Seems to be lots of excitement about 1 piece of a massively complicated jigsaw.

 

Even accounting for the fact this isn't a 100% correlation for the AO (i.e you may fall in the x% where it's just wrong), picking the AO as a dominant factor in getting cold air to the UK just seems daft*

*Appreciate that this isn't what the research/monitoring of this index is about, just seems to have been adopted by some to that end.

 

As last year showed we still know very little about what makes the weather tick in seasonal terms and if a bunch of extremely clever people with extremely powerful computers can be shown up then I'm not going to be pinning my cold hopes on this particular method of looking at one factor influencing our weather

 

I guess as a method for assessing how one small part of the puzzle may pan out, it's interesting but given how the puzzle works in terms of UK cold (i.e the last piece needed can end up being the one that changes the picture) then it's a very small step on a long, long journey. 

Still cynicism aside I hope it means at least 1 snowfall imby as I want to build a snowman with my daughter

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Part of the reason for the excitement is the very firm correlation between a strongly negative OPI and cold winter months in the UK when the Quasi-Biennial Oscillation is negative (easterly), as it will be this winter.

The problem, of course, is that by adding the QBO filter to the results you reduce even further the already tiny numbers of years of data on which to base conclusions. But it does at least acknowledge another piece to the jigsaw.

I'm not concerned about people with "extremely powerful computers" having been shown up, even if they are "extremely clever". We and they know that their models go off the rails after a week. They lack both the data and the computer power for the result to be any different. By running them out to 6 months they must surely realize they're just trying to find a way to pass the time. An ensemble of 1,000 runs is 1,000 wrong answers. I can't see how any trend displayed by those model runs is down to anything but chance.

But this index is offering something different imo. It's asking whether a certain set of conditions at a certain period of the autumn sets in train a mechanism by which a specific set-up is highly likely to occur at some point in the subsequent months, regardless of other inputs. And for the UK there's speculation that if one of those other inputs is an easterly QBO, then the two ought, on the basis of limited evidence, to combine very nicely indeed if you're after one very cold month.

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Few potential long-range predictors sound more promising than one involving a particular sequence of events unfolding through time as a consequence of one other, with a starting point two months in advance of the target season.

For a truly reliable indicator, however, we would need to know of and fully understand every step along the way. At this stage, I'm not sure how far beyond 'B often happens after A when C is present, by some mechanism' with regards to the OPI.

 

Another promising predictor using a sequence of events is that of snow advance across Asia during October coupled with anomalously low ice cover in the bordering areas of the Arctic Ocean during that same period, but it currently lacks in scientific verification.

 

Perhaps one day these predictors, if successful enough, will be used to weight model forecasts in favour of the patterns being signaled. At least then the right target might be aimed for, even if a bulls-eye remains highly improbable, as will always be the case due to the nature of chaos theory.

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My understanding is that the Snow Advance Index has been subsumed into the October Pattern index. The advance southwards of Eurasian snow in October is reckoned to be determined by the factors which are analysed to calculate the OPI. With this in mind Prof. Cohen, the creator of the SAI, is collaborating with the people behind the OPI on a joint paper to be peer-reviewed.

Regarding the mechanism for A leading to B and C, I suspect that this is an aspect of the study which is subject to peer review and consequently not revealed to us mortals at this stage. But something along the lines of conditions which lead to warm air advecting northwards and waves travelling upwards this month might do the trick. But I'll admit I'm way out of my depth here.

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OPI forecast to be -2.28 after 06z

http://app.til.it/opi/

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This mornings OPI forecast stands at -2.57 with less than a week to go...

http://app.til.it/opi/

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-2.38 at the moment. Definitely going to be negative this year. Should be an interesting test for the index.

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Seems to have settled at around -2.3. If we keep this to the end of the month will be the second most negative OPI since 1976 with only 2009 more negative!

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