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

[MR EXTREMES]

Assuming the final OPI figure is -2.5 or below then the winter of 2009/10 is still the nearest analogue we have for comparison,so i would expect something along the lines of the below charts for their forecast when released.

 

Image.png20092010euro.gif850mbtemps.gif

 

 

There is just a chance it isn't that simple however.

which is the analogue ive punted for since sept,

and although signs are not showing just yet the over all pattern is similar to 09 autumn.

and the model outputs are very much looking messy but far more interesting.

 

i think mid nov early dec will be the time we really start to see where winter is heading.

but the OPI of -2.5 is a good start although -3 or -4 would have been a little more exciting.

[Penrith Snow]

I remember well Autumn 2009 and no one but no one was expecting a very cold winter as the Autumn was very non-descript, only November was noteworthy in that it was exceptionally wet.

Even in early December there were few signs of the cold to come but then mid month pressure built strongly over Scandinavia and the rest is history.

You just can't look at the UK weather in Autumn as an indicator of the winter to come as cold winters have been preceded by all types, however, a strong zonal dominated Autumn is the one not to have.

Andy

[KyleHenry]

which is the analogue ive punted for since sept,

and although signs are not showing just yet the over all pattern is similar to 09 autumn.

and the model outputs are very much looking messy but far more interesting.

 

i think mid nov early dec will be the time we really start to see where winter is heading.

but the OPI of -2.5 is a good start although -3 or -4 would have been a little more exciting.

You have to remember that when the final figure is returned, it will be for the central countries of mainland Europe. Deductions due to geographical location will need to be made for British Isles.

So if a -2.40 is returned and you live in Cornwall at or near sea level for example deductions would equate to approximately -0.8. Further East/North and higher elevation the less deductions and better feel for a more exact anomaly year match.

[Isolated Frost]

As the 00z today takes +168 to get to 00z 1st November, I'd say we've got 2-3 days of any possibility of a spread above 0.8-1.0 (i.e. values dipping below 2.0 or above 3.0), but I think we've got a reliable landing range which means the OPI is going to be the 2nd lowest in its 38 years of recording. And looking at OPI-DJF AO composites, OPI-DJF CET composites, that is, at the very least, a very good start if you're looking for cold this winter.

 

Of course there are many more pieces to the puzzle, but we're at no disadvantage to have one of the lowest OPI values on record.

[ukpaul]

I've noted that the greatest negative figures have usually been on the western side of the map (when they haven't all been at the extreme end, which has been often), that will probably be reflected in the final forecast I would have thought.

[radiohead]

I think the 06Z figure would usually be out by now, so it looks like we won't get that today.

[karyo]

I think the 06Z figure would usually be out by now, so it looks like we won't get that today.

The 6z had big differences compared to the 0z. There was blocking in the arctic in the 6z so a bit of a shame that it was discarded. Still, we can't complain... :-)

[knocker]

The 6z had big differences compared to the 0z. There was blocking in the arctic in the 6z so a bit of a shame that it was discarded. Still, we can't complain... :-)

 

Bit of a stretch calling that blocking.

[karyo]

Bit of a stretch calling that blocking.

Maybe you can enlighten me with your definition of blocking!

[knocker]

Maybe you can enlighten me with your definition of blocking!

 

If you insist. Blocks are specific patterns which cause the long wave flow to become stationary for days or weeks at a time. Maybe you can enlighten me with your definition of blocking.

[karyo]

If you insist. Blocks are specific patterns which cause the long wave flow to become stationary for days or weeks at a time. Maybe you can enlighten me with your definition of blocking.

What the 6z shows! High pressure cells able to divert or slow down significantly the prevailing flow of the jet stream. 

[knocker]

What the 6z shows! High pressure cells able to divert or slow down significantly the prevailing flow of the jet stream. 

 

We are going to have to agree to differ as I don't see how one chart can be described as blocking. In any case as far as I can see the jet ( I didn't realise you were specifically talking about the jet) is whizzing around the LP around Greenland at about 120kts.

Edited October 25, 2014 by knocker

[stewfox]

Just going to post the OPI link for those who may have missed it many pages back

 

A fascinating thread

 

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

[MR EXTREMES]

What the 6z shows! High pressure cells able to divert or slow down significantly the prevailing flow of the jet stream. 

i agree karyo in other words anything thats blocking progression of low pressure systems.

 thats not a low pressure system showing on that gefs chart thats higher pressure than low.

[Isolated Frost]

12z OPI @ -2.20

[MR EXTREMES]

i agree karyo in other words anything thats blocking progression of low pressure systems.

 thats not a low pressure system showing on that gefs chart thats higher pressure than low.

this is a weak block

tonights gefs although fi is not bad for the OPI

[radiohead]

12z OPI @ -2.20

 

Looking good for a final OPI between -2 and -2.5. I doubt we'll see much change from that now.

[Ali1977]

Feel a bit disappointed at -2.2, even though this is still a low OPI.

[Duane S.]

-2.2 will be a stunning final figure, think it may ultimately creep a bit closer to the -2 mark but stay the right side. I see a bit more of Central Europe has been coloured in as well.

[Ali1977]

Why is the UK never coloured in? Is this as we are often on the edge of cold weather so harder to forecast?

[Crocodile23]

Why is the UK never coloured in? Is this as we are often on the edge of cold weather so harder to forecast?

 

 From what i understand from the paper, they have selected this area as they've found a strong correlation of the winter's geopotential heights there, with October's OPI. Here is the google translation of what it says in the paper(that was written in Italian):

 

 

Google translation:

Just about to central-western, it was possible validate, even in numerically, the predictive power of OPI, referring to the parameter of the fault geopotential average calculated on the winter quarter. The latter, for each year was calculated again using the maps available for download from the archives NCEP reanalysis using software Telemappa NG. The reference sample is always including the years 1976 to 2012, while the European area subject to analysis is shown in the following figure:

[karyo]

this is a weak block

tonights gefs although fi is not bad for the OPI

Yes agreed, but thnkfully that's the end of the month and a pretty good OPI is secure now.

[Isolated Frost]

Why is the UK never coloured in? Is this as we are often on the edge of cold weather so harder to forecast?

EU are anti-British.

[Man With Beard]

-2.2 will be a stunning final figure, think it may ultimately creep a bit closer to the -2 mark but stay the right side. I see a bit more of Central Europe has been coloured in as well.

It's this European map that interests me more than anything. A negative 500hpa anomaly over central Europe, focused on France where the most extreme anomaly possible is registered? What kind of pattern could produce that? Sounds like high-level blocking anywhere from Greenland to Scandinavia - that would mean winds often somewhere between a northerly and an easterly, with lows either moving east to west, north to south or underneath the block on a southerly jet. Or maybe just maybe cold zonality with a jet from Iceland down to Southern Europe (seems unlikely though). They are all cold options, though the latter one could be a bit less cold and quite stormy.

(Disclaimer! I'm not saying ALL winter, I'm just saying for the OPI map of Europe to be correct, we would expect such patterns at least SOME of the time).

Or am I missing something? Thoughts please!

Edited October 25, 2014 by rjbw

[Gael_Force]

It's this European map that interests me more than anything. A negative 500hpa anomaly over central Europe, focused on France where the most extreme anomaly possible is registered? What kind of pattern could produce that? Sounds like high-level blocking anywhere from Greenland to Scandinavia - that would mean winds often somewhere between a northerly and an easterly, with lows either moving east to west, north to south or underneath the block on a southerly jet. Or maybe just maybe cold zonality with a jet from Iceland down to Southern Europe (seems unlikely though). They are all cold options, though the latter one could be a bit less cold and quite stormy.

(Disclaimer! I'm not saying ALL winter, I'm just saying for the OPI map of Europe to be correct, we would expect such patterns at least SOME of the time).

Or am I missing something? Thoughts please!

 

I would think some of the recent winters might be an example where we have watched the cold slide south into France from a north easterly direction. I can only think that the anomaly is greatest in France as it is usually the first port of call of the Azores ridge which has been the predominant pattern in the period of climatology on the composites the OPI uses. ie 81 -10.