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

[bobbydog]

A fairly substantial cover to the NE as well at the end of next week..........

 

http://www2.wetter3.de/Animation_12_UTC/192_35.gif

  

Let's 'Av it'.  This will be a very interesting winter if trends continue.....a few theories will be tested

 

BFTP

Well, as far as i can see, the correlation between the OPI and the AO runs almost parallel to the correlation between the October SAI and the AO. Bearing in mind, at this point the snow advance is not far off DOUBLE the value of any other october in the past 15 years and the forecast is for more snow in the crucial areas, if it continues on track, the OPI figure should be well into negative values by the end of the month. We could potentially be looking at all the right ingredients for an epic winter....

[OlaL]

-1,5 or lower will do!

 

I would certainly take one of these winters, which are the ones with OPI<-1,5

 

1976/77

1978/79

1984/85

1985/86

2009/10

2012/13

 

Out Of these 18 months, only 1 above normal for my area (Dec 1984).

 

-1,5 seems to be a break point where you go from unclear signal(big spread in the plot), to clear signal (colder than normal).

[summer blizzard]

Suggested average for the AO based on todays runs suggests an AO value near -1.5. Good company with 2009 and 2012.

[easton888]

-2.92 on the 00z

[Blessed Weather]

Good to see the Index back on track! Given that we know what the Nth hemisphere 500hPa mean height anomalies looked like for the ten most negative OPI Octobers, and we know that the OPI calculation includes 10 forecast charts from GFS, then an encouraging indicator as to how the Index might progress will be to look at the GFS 8-10 day forecast height anomalies and compare with the Top Ten composite. So here's the latest comparison.

 

First the composite for the most negative OPI Octobers (with thanks to BFTV for posting earlier in the thread). It's low heights for Russia, south of Greenland and south of the Aleutians, and positive heights over the Pole:

 

Then yesterday’s 12z ECM/GFS 8-10 day mean height anomalies. (GFS on the right). There are a number of ticks in the box although some anomalies are slightly out of position.

 

So good to see the heights maintained over the Pole and the Vortex still disturbed. It bodes well. But the unknown going forward is how  any slight misplacement of anomalies and “wrong†inclination of vortex lobes will impact the Index calculations.

[KyleHenry]

I'm still waiting to see how the ACE index results this season.

The big concern for a substantially negative OPI is the upsurge in Atlantic and Pacific TD/ Hurricanes and what effect moisture transfer has to snow cover below 60N

At present these systems are zeroing in to northerly latitudes for last 10 days October

[summer blizzard]

I'm still waiting to see how the ACE index results this season.

The big concern for a substantially negative OPI is the upsurge in Atlantic and Pacific TD/ Hurricanes and what effect moisture transfer has to snow cover below 60N

At present these systems are zeroing in to northerly latitudes for last 10 days October

 

High global ACE is correlated with more ozone transport and a -AO (though not the strongest link). We do i believe have high global ACE although the Atlantic itself will finish below average.

[Bobby]

Good to see the Index back on track! Given that we know what the Nth hemisphere 500hPa mean height anomalies looked like for the ten most negative OPI Octobers, and we know that the OPI calculation includes 10 forecast charts from GFS, then an encouraging indicator as to how the Index might progress will be to look at the GFS 8-10 day forecast height anomalies and compare with the Top Ten composite. So here's the latest comparison.

 

First the composite for the most negative OPI Octobers (with thanks to BFTV for posting earlier in the thread). It's low heights for Russia, south of Greenland and south of the Aleutians, and positive heights over the Pole:

Oct Hgt Anomalies Mean for Top Ten -ve OPI winters.png

 

Then yesterday’s 12z ECM/GFS 8-10 day mean height anomalies. (GFS on the right). There are a number of ticks in the box although some anomalies are slightly out of position.

ECM-GFS 8-10 Mean 500 Hgt Anomaly on 14Oct2014 marked.jpg

 

So good to see the heights maintained over the Pole and the Vortex still disturbed. It bodes well. But the unknown going forward is how  any slight misplacement of anomalies and “wrong†inclination of vortex lobes will impact the Index calculations.

 

The ECM ENS anomaly/mean is showing the vortex organising and getting especially marked over Greenland at day 10. This is not great news? I would expect an active Atlantic from that with cold air being sucked south firing up the jet

 

 

[karyo]

The ECM ENS anomaly/mean is showing the vortex organising and getting especially marked over Greenland at day 10. This is not great news? I would expect an active Atlantic from that with cold air being sucked south firing up the jet

 

 

Well, at day 10 it won't be much of a concern as it will be the 25th October by then! As long as we get decently negative figures every day till then we will be fine with the final figure. That's assuming that day 10 will come off.

 

As for the 6z gfs, it has less high pressure in the Arctic than the 0z so I expect it to have a higher OPI once again but it should still be negative.

 

Karyo

[mulzy]

Well, at day 10 it won't be much of a concern as it will be the 25th October by then! As long as we get decently negative figures every day till then we will be fine with the final figure. That's assuming that day 10 will come off.

 

As for the 6z gfs, it has less high pressure in the Arctic than the 0z so I expect it to have a higher OPI once again but it should still be negative.

 

Karyo

the 6z (15th) gives an OPI of -2.70 so only slightly less negative...

[karyo]

the 6z (15th) gives an OPI of -2.70 so only slightly less negative...

Indeed! Much better than I was expecting and lower than yesterday's 6z index!

[LomondSnowstorm]

The ECM ENS anomaly/mean is showing the vortex organising and getting especially marked over Greenland at day 10. This is not great news? I would expect an active Atlantic from that with cold air being sucked south firing up the jet

 

 

 

I think as long as the positive anomalies are prevalent over the pole we're not going to push the value up that much, even with the vortex starting to look a bit more established over Greenland. It would be utterly incredible if we got to the end of October without any signs of vortex formation - even record breakingly negative OPI month October 2009 finished similarly to the chart shown above:

[easton888]

-2.70 on 12z

[Gael_Force]

I'm no expert on this but a mean of fifty ensemble members will show nothing on the NH view as the ridge patterns are blurred out by so many different nuances of placement.

 

The 2009 reanalysis seems to be the the perfect bench mark for what Riccardo was talking about in the 1984/5 study - wave two breaking from Pacific to Atlantic.

 

Can anyone remember the discussion about the split vortex on that axis? Something along the lines of the jet stream not crossing and thereby allowing retrogression of the weather from the east.

[Man With Beard]

The ECM ENS anomaly/mean is showing the vortex organising and getting especially marked over Greenland at day 10. This is not great news? I would expect an active Atlantic from that with cold air being sucked south firing up the jet

 

 

It should be added though ... this isn't the first time the models have tried to beef things up by D10. They may be overdoing it due to model seasonal bias - particularly if this season is not going to be the same as "average" seasons?

 

Great thread btw ... if the OPI gets this winter right, I sense model watching in October will never be the same again!

Edited October 15, 2014 by rjbw

[SMU]

Afternoon.

 

Based on todays OPI landing @2.70 - then the midpoint of the month arrives at -1.993 ( lets be generous & round it up to 2)

That's 15 days & -30 in total.

 

In terms of the 'league table' of negative OPI's this would place 2014 in second place....

 

1st 2009  -3.4

2nd 2014 -2.0    Midpoint

3rd 1985 -1.9

4th 2012,1976,1978

 

Here is the landing zone prediction.

 

 

The outer Markers are -1 & -3 with a realistic cone being at -1.5 to -2.5

*** IF we land at -2 or below*** Then the statistical probability based on the sample size from November 1976 to date is -

 

there is 80% Chance of all Months being all Months being NEGATIVE AO

There is near on 100% chance of 2 Months being NEGATIVE AO

 

Theres also more to reveal but that comes later

 

S

Edited October 15, 2014 by Steve Murr

[easton888]

Quick question: Of these top -AO winters (1977, 1985, 2009) at what time roughly did the cold and snow arrive to our shores?

[Weather-history]

Quick question: Of these top -AO winters (1977, 1985, 2009) at what time roughly did the cold and snow arrive to our shores?

Both 1976-77 and 2009-10, cold and snow arrived before Christmas.

December 1976 was cold with a CET of 2.0C but you never hear much about it.

1984-85, the cold and snow came very shortly after New Year

[NorthernRab]

I think the cold arrived to the Scottish Highlands first from the north in 2009? Around the 18/19th? I was on my way home from university for Christmas as a fragment of the polar vortex was dropping down from the north - heavy snow with sub zero day time maxes and a further spell of very heavy snow on the 23rd. Think it stayed below freezing until the 13th of January with lots of lying snow.

Edit: very heavy snow on Boxing Day and New Year's Eve as well, I've just remembered! The New Year street party was cancelled in Inverness.

Edited October 15, 2014 by NorthernRab

[damianslaw]

Both 1976-77 and 2009-10, cold and snow arrived before Christmas.

December 1976 was cold with a CET of 2.0C but you never hear much about it.

1984-85, the cold and snow came very shortly after New Year

 

Incidentally the very negative October of 2009 was followed by the wettest November on record for many, and here the wettest month on record. It was also one of the mildest Novembers on record. We saw a marked longwave trough become rather unstuck over the mid eastern atlantic feeding in very mild southerly/southwesterly airstreams. I wasn't paying much attention to the position and strength of the PV at the time, but I do remember thinking things were not normal service, given the extreme rainfall totals and exceptionally slow moving frontal action. There was significant warm air advection over Scandinavia and into the Pole region due to this pattern and I would have expected this helped increase the chances of strong height development to the north. The pattern change around the 9th-12th Dec was quite unusual with a rather innocuous ridge from the azores suddenly becoming a power juggernaut and quickly building to envelop the whole country and Scandanavia - I certainly wasn't expecting such a synoptical evolution and neither were many long range forecasts.

[LomondSnowstorm]

I think the cold arrived to the Scottish Highlands first from the north in 2009? Around the 18/19th? I was on my way home from university for Christmas as a fragment of the polar vortex was dropping down from the north - heavy snow with sub zero day time maxes and a further spell of very heavy snow on the 23rd. Think it stayed below freezing until the 13th of January with lots of lying snow.

Edit: very heavy snow on Boxing Day and New Year's Eve as well, I've just remembered! The New Year street party was cancelled in Inverness.

The first snowfall of December '09 was from an easterly on the 17th which gave about 1-2 inches down the east coast, the northerly came on the 18th/19th before the cold trough/PV fragmeg sat over us right through to Christmas bringing exceptionally low minima and snow from troughs embedded in the flow. Most notably for us at least was the 22nd/23rd, when minima of widely -10C by 8pm gave way to 4-8 inches snow across Eastern Scotland, with some of the deepest snow seen in Edinburgh in years (pre-December 2010). I think it wasn't so bad south of Newcastle and there was a thaw ranging in length from about 10 days in Southwest England to a few hours south of the Forth, and none at all north of that. January became much more severe south of the border and was a continuation of the intense cold and steady snow accumulation in Scotland up to the 14th, when there was a gradual breakdown when the cold pool to the east simply ran out.

[Yarmy]

The first snowfall of December '09 was from an easterly on the 17th which gave about 1-2 inches down the east coast, the northerly came on the 18th/19th before the cold trough/PV fragmeg sat over us right through to Christmas bringing exceptionally low minima and snow from troughs embedded in the flow. Most notably for us at least was the 22nd/23rd, when minima of widely -10C by 8pm gave way to 4-8 inches snow across Eastern Scotland, with some of the deepest snow seen in Edinburgh in years (pre-December 2010). I think it wasn't so bad south of Newcastle and there was a thaw ranging in length from about 10 days in Southwest England to a few hours south of the Forth, and none at all north of that. January became much more severe south of the border and was a continuation of the intense cold and steady snow accumulation in Scotland up to the 14th, when there was a gradual breakdown when the cold pool to the east simply ran out.

Way more than 1-2 inches in Norfolk on the 17th. The Wash streamer effect produced a bonanza.

-2.70 on 12z

06z. The 12z update isn't showing yet.

Edited October 15, 2014 by Yarmy

[Froze were the Days]

Both 1976-77 and 2009-10, cold and snow arrived before Christmas.

December 1976 was cold with a CET of 2.0C but you never hear much about it.

1984-85, the cold and snow came very shortly after New Year

 

OPI for oct 85 @-1.9 would then refer to the following winter 85/86? If so Dec was mild with a cold end, Jan chilly but not exceptionally so and Feb 86 one the coldest of the 20th century.

[bobbydog]

What time does it update?

[karyo]

What time does it update?

It normally updates about an hour after the 12z completes but today it is stuck in the 6z index.