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Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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On 18/01/2020 at 10:43, Blessed Weather said:

Hope not - a strongly positive IOD seems to be a winter killer for the UK (if cold/snow is your preference). Here's the index since 1982 showing 3 previous strong events in 1994, 1997 and 2006.

1816674263_IODIndex1982toDec2019.thumb.gif.3518c71ae1a3398fa7498ee9910c0e37.gif

Source: https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php

And the weather in the winters that followed?

1994/95 - Very mild with a 3-month winter average CET of 5.9C. The summer of 1995 saw a record breaking heatwave.

1997/98 - Very mild with a 3-month winter average CET of 6.1C. Record breaking winter warmth for the UK and Europe.

2006/07 - Very mild with all 3 winter months CET above long term average. This article from Philip Eden:

 

Very interesting, but it can also tie into this other post -

 

On 20/01/2020 at 18:05, Kirkcaldy Weather said:
 
 

A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al -

https://www.netweather.tv/forum/topic/90431-uk-first-ground-and-air-frost-watch-season-2018-2019/?do=findComment&comment=3908027

The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally).

A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC.

At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.

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Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl
3 hours ago, Interitus said:

Very interesting, but it can also tie into this other post -

 

A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al -

https://www.netweather.tv/forum/topic/90431-uk-first-ground-and-air-frost-watch-season-2018-2019/?do=findComment&comment=3908027

The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally).

A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC.

At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.

How can the cold blob turning into a warm one then?

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5 hours ago, damianslaw said:

How can the cold blob turning into a warm one then?

This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 -

cb.thumb.png.6c9f34c34b8ae43467ee8f80e02b9e89.png

Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C.

Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter -

Quote

North Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010

Abstract

Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/10 and in late 2010. These periods were characterized by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global ocean–atmosphere general circulation model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over northern Europe are examined. Different atmospheric responses occur in the winter of 2009/10 and the early winter of 2010. These experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/10. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to a significant shift in the atmospheric circulation over the North Atlantic toward a NAO negative phase. Therefore, these results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase, which culminated in the extreme cold weather conditions experienced over northern Europe in December 2010.

https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1

For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.

Edited by Interitus
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Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl
19 hours ago, Interitus said:

This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 -

cb.thumb.png.6c9f34c34b8ae43467ee8f80e02b9e89.png

Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C.

Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter -

https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1

For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.

Interesting reading, when did the tripole develop then in 2009, through the summer and autumn? normally its SST values in May that indicate likely negative NAO or not.. I think the El Nino modoki was a strong factor for the cold winter of 09/10, it did start mild after a very mild November as well..

2010 was cold throughout with lots of northern blocking which will have helped with warm uppers over N Atlantic.

A blocked spring helps I think with mid atlantic heights, 1995 brought this, and we saw a tripole in winter of 95/96.. did 2005 do the same?, tripole again in winter 2005/2006.

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Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • 2 weeks later...
Posted
  • Location: Exeter, Devon, UK. alt 10m asl
  • Location: Exeter, Devon, UK. alt 10m asl
On 04/02/2020 at 18:36, mushymanrob said:
visual-cortex-globe-temperatures.png
WWW.METOFFICE.GOV.UK

The Madden-Julian Oscillation is characterised by an eastward spread of large regions of enhanced and suppressed tropical rainfall, mainly...

 

I'm going to throw this one in here as well as it has some very good animations to show the different phases.

MJO_610_0.png
WWW.WEATHERNATIONTV.COM

[The surface and upper-atmosphere structure of the MJO for a period when the enhanced convective phase (thunderstorm cloud) is centered across the Indian Ocean

 

 

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Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

World Climate Service tweet 13th Feb:

This is getting ridiculous - peak AO index values in recent ECMWF HRES (10-day) runs:
Feb 12 00Z +6.4
Feb 12 12Z +7.3
Feb 13 00Z +7.6
We've capitulated and expanded the scale on our AO graphics to accommodate the extreme. 1950-present record (set 3 days ago) is +6.3

347725020_ECMWFAOforecast13Feb.thumb.jpg.448981e2a7d6000536b0e792abf56019.jpg

Source: Twitter @WorldClimateSvc

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

Analysis from Dr Amy Butler shows the longer term trend in the Arctic Oscillation from 1950 to date is clearly creeping ever more positive. Nevertheless, some significant periods of negative AO still regularly occurring with winter 2009/10 the most recent event.

363826938_AOtrend1950-2020.thumb.jpg.e295b97acf0ea699b1734f02b4573990.jpg

Source: Twitter @DrAHButler

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

An update on the recent run of extreme positive AO values. The more extreme forecasts from ECM a week ago were not realised, nevertheless the World Climate Service reporting that yesterday (21st Feb 2020) set a new record:

"The positive Arctic Oscillation regime reached a new extreme yesterday, with a daily AO index of +6.5, a new all-time (1950-present) record, and beating the record set/tied 10 days ago."

Source: Twitter @WorldClimateSvc

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  • 2 weeks later...
Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • 4 months later...
Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • 4 weeks later...
Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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Posted
  • Location: Carryduff, County Down 420ft ASL
  • Location: Carryduff, County Down 420ft ASL
10 hours ago, Kirkcaldy Weather said:

 

So, if I recall, the positive phase scuppered a cold Winter, will the negative phase do the opposite? 

Or will some other unknown event scupper Winter this year.

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Posted
  • Location: Essex Riviera aka Burnham
  • Weather Preferences: 30 Degrees of pure British Celsius
  • Location: Essex Riviera aka Burnham
4 hours ago, mountain shadow said:

Or will some other unknown event scupper Winter this year.

Most probably...there always seems to be a reason why we don't get a coldish winter. +SLP in the north east Pacific is prevalent again and has been ongoing since these run of mild winters.

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  • 1 month later...
Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • 6 months later...
Posted
  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • 2 years later...
Posted
  • Location: Gillingham, Kent
  • Weather Preferences: Snow, Thunderstorms,
  • Location: Gillingham, Kent

Wow!

Just skimmed through the first few pages and there's some great posts by @Blessed Weather and others with a lot of resources, will give the thread a proper read through before posting. @Blessed WeatherDo you happen to have a copy of the posts you made over on 33andrain on the GSDM back in the day? Sadly the forum is no longer online but many of your posts were extremely helpful in my understanding of the topic, perhaps you have posted them here already and I've just not read far enough into the thread!

Hopefully this thread can become active again and we can get some decent discussions/debates on all things technical! @Tamara @MattH. I'm not sure the model output thread is quite suited for this kind of topic.

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Posted
  • Location: Herne Bay, Kent (14 m)
  • Weather Preferences: Thunderstorms & Snow
  • Location: Herne Bay, Kent (14 m)

I certainly need to scratch up my crumbs of knowledge on the GSDM so quite happy on the prospect of this becoming more active 😀

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Posted
  • Location: Gillingham, Kent
  • Weather Preferences: Snow, Thunderstorms,
  • Location: Gillingham, Kent

Before we look further ahead let's take a look at what's recently happened. 

u_anom_30.5S-5N.thumb.gif.974070bc8aca003a622d0ccc6f5d58fa.gif

A strong westerly wind burst (WWB) event has just finished in the Pacific, this wind burst event is responsible for a large uptick in AAM tendency (and subsequent rise in AAM) which can be seen here, the timing correlates well with the 850hPa zonal wind anomalies chart above. The left chart shows the rise in AAM tendency and the second chart shows the subsequent rise in global AAM (GLAAM) which followed.

2.thumb.png.8cfd8275cb4840329554780151a6bd5b.png1.thumb.png.f36f5c0e347a18e3e3a86c94f6bcfb8f.png

The WWB has faded and easterlies have returned just west of the dateline, as a result AAM tendency has fallen through the floor and GLAAM will begin falling again, likely back into neutral or negative territory, this can be seen on the above two charts too. The main trigger for this is convection emerging in the Indian Ocean (MJO) scrubbing the atmosphere of westerly inertia from the recent WWB. 

During this timeframe the MJO was emerging into a very weakly amplified phase 8.

mjo_rmm.daily.20231116.thumb.png.fb3ef1f32b74a82f41ef1f79bdda1185.png

Rising AAM tendency signals an increase in westerly momentum within the global wind-flow budget, higher westerly momentum can lead to a more perturbed jet stream with phase 8 MJO roughly correlating to a mid Atlantic ridge, I've posted both the El Nino composite & the neutral ENSO composite below given the atmosphere is behaving somewhere between the two. 

nina_8_nov_low.thumb.png.7d0b68b7fa9b20e399797424e9d79bb4.pngnada_8_nov_low.thumb.png.cb25cc16e0ca94ccbfa7ae41bb0e5f68.png

If we compare the above composites with the latest GFS forecast there are some similarities, not an exact match but that's to be expected given the very weak amplitude MJO. The high is a little more amplified in the forecast vs the composites and I suspect this is due to +ve westerly momentum perturbing the jet stream.

gfsnh-0-156.thumb.png.f740de7216183f5de371cf4a14da04b0.png

Broadly speaking then, no real "oomph" to transition the high from a mid-latitude HP to a high latitude HP and as such despite some over-enthusiastic NWP modelling, the signal for a Greenland high hasn't been particularly well supported when taking into account all models and ensemble suites. Going forward, a fall in AAM and the MJO cycling through phases 1-2-3 suggests a return to zonal/Atlantic driven weather through early December but perhaps with the Azores high occasionally extending NEwards into southern parts of England.

Another thing to consider is the -QBO which is continuing to down well. I suspect this is helping to temper the SPV from properly coupling with the troposphere giving us a small window where tropospheric blocking (albeit mostly mid-latitude due to lack of tropical forcing) is favourable.

3.thumb.png.0a1001ec5c4d834ae3ea3aebe73a69b9.png

Will do a post tomorrow about the likely evolution of the MJO & AAM through December and when things could potentially get a little more interesting. 

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