OCTOBER PATTERN INDEX (OPI) MONITORING WINTER SEASON 2014-2015

[neige57]

Maybe if it was based on the ECM ensemble mean instead of GFS op runs,things might be a bit smoother,although

that would probably rob us of the sub -3 OPI goodness!

 

 

This could really help the Nordic block is the QBO to highly negative values ​​now, even at the records, between -25 and -30. And it should especially continue for several months. I think we are heading towards an interesting winter in Europe. The only question mark is solar activity but it is spirit to fall sharply at the moment so a rather positive

[bluearmy]

Maybe if it was based on the ECM ensemble mean instead of GFS op runs,things might be a bit smoother,although

that would probably rob us of the sub -3 OPI goodness!

I assume Riccardo and his team have used other models to assess the differences. maybe he could enlighten us as to the variance that they show. Across the polar field it may be less significant than you might think.

[feb1991blizzard]

I assume Riccardo and his team have used other models to assess the differences. maybe he could enlighten us as to the variance that they show. Across the polar field it may be less significant than you might think.

 

Yes, I think there is far less inter model difference wrt 500mb height anomalies across the whole of the NH than just for our neck of the woods, where the ECMWF is clearly king.

[LomondSnowstorm]

A good demonstration of the inter-run volatility that the operational GFS is throwing out in the Arctic - OPI back down to -3.15, having been up above -1 for the first time since the 3rd on the 6Z:

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

[BLAST FROM THE PAST]

This could really help the Nordic block is the QBO to highly negative values ​​now, even at the records, between -25 and -30. And it should especially continue for several months. I think we are heading towards an interesting winter in Europe. The only question mark is solar activity but it is spirit to fall sharply at the moment so a rather positive

Why is solar activity a question mark?.  Its at or just past its maxima BUT for a maxima it is LOW......and its entering an overall deep minima and is likely why the Jetstream is generally further south and meridional.

 

 

 

BFTP

[Polar Maritime]

Yes Fred, And adding in lagging time the recent months/few years should certainly have an effect. With activity dropping and forecast to drop over the coming months, Not having an immediate effect as such..  

Edited October 12, 2014 by Polar Maritime

[karyo]

A good demonstration of the inter-run volatility that the operational GFS is throwing out in the Arctic - OPI back down to -3.15, having been up above -1 for the first time since the 3rd on the 6Z:

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

Indeed! But I am just glad it is well below 0 again! As we head to the 2nd half of the month it should stabilise like it did last year (but hopefully negative this time).

 

Karyo

[chionomaniac]

This was copied and posted on an Italian weather forum on 28th October, so pretty much the final article.

 

 

It seems to me that last year the OPI seemed to settle and remained fixed in the outlook from mid month onwards - I guess that we need to hope that the negative OPI forecast so far this year will remain and do the same following mid month.

At a guess, until the average establishes itself the axis angle will be very sensitive to changes in pressure pattern, far more so than the changes in GPH and it is also the larger contributor to the overall value.

Great earlier post regarding the angle that is all important in the OPI calculation. It seems that this weekend the OPI forecast has suffered somewhat with GFSitis.... I  wonder how difficult it is to analyse the different runs and see where that different angulation of the vortex comes into play.

Edited October 12, 2014 by chionomaniac

[ukpaul]

A good demonstration of the inter-run volatility that the operational GFS is throwing out in the Arctic - OPI back down to -3.15, having been up above -1 for the first time since the 3rd on the 6Z:

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

 

Well, I'm pretty much lost as to the calculations and what the runs show, I glanced at the 12z and thought it was a poorer long term pattern for high pressure in the right places!

[neige57]

It seems to me that last year the OPI seemed to settle and remained fixed in the outlook from mid month onwards - I guess that we need to hope that the negative OPI forecast so far this year will remain and do the same following mid month.

Great earlier post regarding the angle that is all important in the OPI calculation. It seems that this weekend the OPI forecast has suffered somewhat with GFSitis.... I  wonder how difficult it is to analyse the different runs and see where that different angulation of the vortex comes into play.

 

yes it is true but this time, we are in a very negative and near record QBO ie between -25 and -30 now so I am much more optimistic that these waves wave 1 (or 2) change things so different to 2013

[Mike Poole]

Maybe if it was based on the ECM ensemble mean instead of GFS op runs,things might be a bit smoother,although

that would probably rob us of the sub -3 OPI goodness!

I presume its based on GFS because the data is freely available.  Whether to use an ensemble mean is more interesting - its the mean of a large number of entirely physical realisations, but the mean itself is not physically reasonable - it could not have occurred in nature - so I don't think it would be useful for this OPI index which looks to be highly dependent on detail.

[bluearmy]

Well, I'm pretty much lost as to the calculations and what the runs show, I glanced at the 12z and thought it was a poorer long term pattern for high pressure in the right places!

 

paul - remember that the opi is not using pressure but the geopotential height at 500mb. look at the colours on the charts rather than the location of high and lows. the polar vortex doesnt always reside where there is low pressure.

[ukpaul]

paul - remember that the opi is not using pressure but the geopotential height at 500mb. look at the colours on the charts rather than the location of high and lows. the polar vortex doesnt always reside where there is low pressure.

 Ah, right. Misconception sorted....

[Mike Poole]

This is an utterly compelling thread!

 

The OPI evolution is simultaneously both fascinating and maddening!  I've been giving some thought to the wild swings we've seen - on Friday and again today.  Some thoughts:

 

I'm taking as read that the OPI is as stated in Riccardo's post i.e. that today's value is average of 12 days actual data + 10 days GFS forecast data.  The swing today from the 06Z to the 12Z was from -0.64 to -3.15.  Given the GFS can forecast pretty well up to 4 days out, the change must largely come from 6 days out of 22.  What could explain this? 

 

I think the answer must be that this is a highly non-linear index - the translation by Interitus a few posts above seems to suggest this regarding the angular position of this axis parameter.  So I conclude that a few days contribute massively to the negative values we see and most others much less so.  Given at day 12/22 we are still seeing massive swings suggests that the values south of -3 have probably arisen mostly from the forecast part rather than the 'banked part' of the index, and the forecast ones from earlier in the month didn't verify.  On that basis I'd guess we'd finish up about -1.5.  Which is nice.

[Nouska]

My interpretation may be way off, but as I currently understand the ideal is to have wave 2 activity to split the polar vortex. To this end it is important to have the two ridges opposite one another - from Pacific to Atlantic. The very low analogue years have that cross polar strip of positive heights - Aleutians to Scandinavia - I suspect Greenland to Kamchatka would fit the bill as well. In some recent runs, that has been observed, in others the angle is offset to some degree.

[SMU]

I think I am going to bow out of the daily ups & downs as im getting a little frustrated with the large changes in daily figures that have been evident across the last 2 days.

 

We looked yesterday how the OPI index at the top is supposed to show the rolling average + 10 days GFS- however the swings seemed a LONG way out of kilter with what was possible within a swing across days 5-10

 

So it was assumed that the index at the top just showed the day-

 

In terms of Geopotential anomalies & vortex going from -0.67 & then back to -3.15 today suggests that the presentation is 100% NOT showing the days average because the GFS between T0 on 06z & T0 on the 12z has next to zero change apart from the small initialization changes.

 

This the leads us back to, what the author presented which was the rolling average + 10, & as mentioned above more so than the geopotential anomalies, the elliptical angle can show large amounts of variation at day 5- so perhaps this is our issue.

 

The rolling average based on the current OPI index out to day 12 is...

 

1.25,0.75,0.25,0.2,2.15,2.1,3.4,3.6,3.8,1.2,1.95,3.15 = 23.8 / 12     -1.98 ROLLING

 

Cheers

S

Edited October 12, 2014 by Steve Murr

[bluearmy]

My interpretation may be way off, but as I currently understand the ideal is to have wave 2 activity to split the polar vortex. To this end it is important to have the two ridges opposite one another - from Pacific to Atlantic. The very low analogue years have that cross polar strip of positive heights - Aleutians to Scandinavia - I suspect Greenland to Kamchatka would fit the bill as well. In some recent runs, that has been observed, in others the angle is offset to some degree.

 

the 12z ecm op seems to be headed that way (if it were to verify which it wont!) 

[chionomaniac]

I think I am going to bow out of the daily ups & downs as im getting a little frustrated with the large changes in daily figures that have been evident across the last 2 days.

 

We looked yesterday how the OPI index at the top is supposed to show the rolling average + 10 days GFS- however the swings seemed a LONG way out of kilter with what was possible within a swing across days 5-10

 

So it was assumed that the index at the top just showed the day-

 

In terms of Geopotential anomalies & vortex going from -0.67 & then back to -3.15 today suggests that the presentation is 100% NOT showing the days average because the GFS between T0 on 06z & T0 on the 12z has next to zero change apart from the small initialization changes.

 

This the leads us back to, what the author presented which was the rolling average + 10, & as mentioned above more so than the geopotential anomalies, the elliptical angle can show large amounts of variation at day 5- so perhaps this is our issue.

 

The rolling average based on the current OPI index out to day 12 is...

 

1.25,0.75,0.25,0.2,2.15,2.1,3.4,3.6,3.8,1.2,1.95,3.15 = 23.8 / 12     -1.98 ROLLING

 

Cheers

S

Steve - where are you getting those daily OPI figures from?

 

If it is from here:

 

 

then I suspect that these are not the daily OPI figures for those particular days but rather the daily OPI forecasts given each day. So we don't actually know that rolling average! Frustrating!

[radiohead]

Steve - where are you getting those daily OPI figures from?

 

If it is from here:

 

Image-1.png

 

then I suspect that these are not the daily OPI figures for those particular days but rather the daily OPI forecasts given each day. So we don't actually know that rolling average! Frustrating!

 

To add to the frustration, the 12Z output seems to overwrite the 06Z number for each day and I don't recall ever seeing 0Z numbers either.

[bluearmy]

my earlier post re sanity on the forum seems to be well on its way to becoming one of my more perceptive ones ! several of the more informed members seem to be struggling. what hope for the rest of us !

[johnholmes]

my earlier post re sanity on the forum seems to be well on its way to becoming one of my more perceptive ones ! several of the more informed members seem to be struggling. what hope for the rest of us !

 

Yes I feel the same ba, 2+2=4 alsways has, always will,no one seems clear just what the daily figures show. Until then it is a bit of a waste of time postulating what might happen as a result of these figures. Best to wait until the last day of the month perhaps?

[DAVID SNOW]

Yes that was really my point: the GFS  can be very good at 'short range' but the further it forecasts,  it can  swing wildly it its output. I think I will wait for the final figure at the end of October.........

 

 I think I got there before you BA with that assumption

[Polar Maritime]

 

 

I think I am going to bow out of the daily ups & downs as im getting a little frustrated with the large changes in daily figures that have been evident across the last 2 days.

 

As always S, At this time year regarding these complicated background signals.. Lot's of chopping and changing, As interesting and valuable as it is. 

[Cloud 10]

I suppose the only thing which really matters is the final figure at the end of the month.

 

I feel like i'm riding the roller-coaster before the track has been built.!

[Interitus]

To add to the frustration, the 12Z output seems to overwrite the 06Z number for each day and I don't recall ever seeing 0Z numbers either.

 

Regarding the scores, each time I think we are seeing the latest score which is composed of all the previous days reanalysis plus the latest 10 days forecast. This latest score eg. from 12Z thus overwrites 6Z and becomes the final score for a particular day. By the last day of the month this will then be the final overall score.

Also this is effectively a running total already, there is no need to calculate it separately.