Stratosphere and Polar Vortex Watch 2020

[damianslaw]

1 hour ago, Catacol said:

Cant quite see it Jules. Looks like a long wave pattern set to give Europe a mild one. Average perhaps over Scandy. We are probably, once again, looking at putting our eggs into a strat warming event to shake things up. As others have said - a substantial north pacific high is signalled and we don't want that. Look perhaps for more of a low over the aleutians in the autumn to help setup strat disruption. If it doesn't then we best get praying, because this mid winter ensemble mean is about as bad as it could be for cold lovers.

It has been a long time since the UK had a proper cold spell not created by a strat warming. 

But as others have said - it is still early.

When was the last time we had a cold spell not caused by strat warming. I suspect most have been caused by them going way way way back...

Edited September 6, 2021 by damianslaw

[Cheshire Freeze]

On 06/09/2021 at 21:16, Catacol said:

Cant quite see it Jules. Looks like a long wave pattern set to give Europe a mild one. Average perhaps over Scandy. We are probably, once again, looking at putting our eggs into a strat warming event to shake things up. As others have said - a substantial north pacific high is signalled and we don't want that. Look perhaps for more of a low over the aleutians in the autumn to help setup strat disruption. If it doesn't then we best get praying, because this mid winter ensemble mean is about as bad as it could be for cold lovers.

It has been a long time since the UK had a proper cold spell not created by a strat warming. 

But as others have said - it is still early.

Have to agree...not many positives in that update. It's about as mild and southwesterly as you can get.

[jules216]

11 hours ago, Catacol said:

Cant quite see it Jules. Looks like a long wave pattern set to give Europe a mild one. Average perhaps over Scandy. We are probably, once again, looking at putting our eggs into a strat warming event to shake things up. As others have said - a substantial north pacific high is signalled and we don't want that. Look perhaps for more of a low over the aleutians in the autumn to help setup strat disruption. If it doesn't then we best get praying, because this mid winter ensemble mean is about as bad as it could be for cold lovers.

It has been a long time since the UK had a proper cold spell not created by a strat warming. 

But as others have said - it is still early.

How about coldest spring since 1997 here in central Europe.Did ECMWF or UKMO pick it up? No,all it needes was record long MJO phase 7 in April to cement meridional flow in Europe. Iam not pesimistic of early wintry spells, dont forget we have slight -IOD in autumn peaking in Oct/Nov,that correlates with precipitiation around Indonesia and Australia(MJO 4-7) Models wont see the MJO activity well now,as they didnt see it back in late Feb for April cold. I am more focused on early cold this year not the post SSW two week spell in February.

[knocker]

Emergence of representative signals for sudden stratospheric warmings beyond current predictable lead times

Abstract

Major sudden stratospheric warmings (SSWs) are extreme wintertime circulation events of the Arctic stratosphere that are accompanied by a breakdown of the polar vortex and are considered an important source of predictability of tropospheric weather on subseasonal to seasonal timescales over the Northern Hemisphere midlatitudes and high latitudes. However, SSWs themselves are difficult to predict, with a predictability limit of around 1 to 2 weeks. The predictability limit for determining the type of event, i.e., wave-1 or wave-2 events, is even shorter. Here we analyze the dynamics of the vortex breakdown and look for early signs of the vortex deceleration process at lead times beyond the current predictability limit of SSWs. To this end, we employ a mode decomposition analysis to study the potential vorticity (PV) equation on the 850 K isentropic surface by decomposing each term in the PV equation using the empirical orthogonal functions of the PV. The first principal component (PC) is an indicator of the strength of the polar vortex and starts to increase from around 25 d before the onset of SSWs, indicating a deceleration of the polar vortex. A budget analysis based on the mode decomposition is then used to characterize the contribution of the linear and nonlinear PV advection terms to the rate of change (tendency) of the first PC. The linear PV advection term is the main contributor to the PC tendency at 25 to 15 d before the onset of SSW events for both wave-1 and wave-2 events. The nonlinear PV advection term becomes important between 15 and 1 d before the onset of wave-2 events, while the linear PV advection term continues to be the main contributor for wave-1 events. By linking the PV advection to the PV flux, we find that the linear PV flux is important for both types of SSWs from 25 to 15 d prior to the events but with different wave-2 spatial patterns, while the nonlinear PV flux displays a wave-3 wave pattern, which finally leads to a split of the polar vortex. Early signs of SSW events arise before the 1- to 2-week prediction limit currently observed in state-of-the-art prediction systems, while signs for the type of event arise at least 1 week before the event onset.

https://wcd.copernicus.org/articles/2/841/2021/

[Yarmy]

Never mind MJO phases, ENSO forecasts or long range ensemble means: the Tesco delivery driver told me, apropos of nothing, that it was going to be the coldest winter in decades as he handed over my comestibles this evening.

So there’s that.

[Catacol]

On 06/09/2021 at 22:23, damianslaw said:

When was the last time we had a cold spell not caused by strat warming. I suspect most have been caused by them going way way way back...

True enough.... though "classic" spells in 1991 and 1996 were not preceded by an SSW. Even the 62/63 winter didn't have an official SSW until the very end of January. I guess I just retain a hope that we might see Glosea pressure predictions to tickle the toes. Remember this one from 2013? Winter turned out to be pretty poor, for me at least, but the glosea ensemble charts got the juices flowing....

However things have changed since 91 and 96. I think the chances of a cold winter in the UK without frictional impacts from descending stratospheric events are now very slim. It may be that these stratospheric warming events get more extreme along with everything else in weather, giving us the possibility of more Feb/Mar 2018 style events surrounded by multiple winters of dross - and that lure of the rare diamond is what keeps me coming back each winter in the face of the misery of a warming planet. Feb/Mar 18 happening 6 weeks earlier would have been extremely significant. As it was it was damned impressive.

 

 

[Ols500]

On 07/09/2021 at 22:25, Yarmy said:

Never mind MJO phases, ENSO forecasts or long range ensemble means: the Tesco delivery driver told me, apropos of nothing, that it was going to be the coldest winter in decades as he handed over my comestibles this evening.

So there’s that.

Well thats it then. -20c 850s over us for 3 months starting in december

[damianslaw]

1 hour ago, Catacol said:

True enough.... though "classic" spells in 1991 and 1996 were not preceded by an SSW. Even the 62/63 winter didn't have an official SSW until the very end of January. I guess I just retain a hope that we might see Glosea pressure predictions to tickle the toes. Remember this one from 2013? Winter turned out to be pretty poor, for me at least, but the glosea ensemble charts got the juices flowing....

However things have changed since 91 and 96. I think the chances of a cold winter in the UK without frictional impacts from descending stratospheric events are now very slim. It may be that these stratospheric warming events get more extreme along with everything else in weather, giving us the possibility of more Feb/Mar 2018 style events surrounded by multiple winters of dross - and that lure of the rare diamond is what keeps me coming back each winter in the face of the misery of a warming planet. Feb/Mar 18 happening 6 weeks earlier would have been extremely significant. As it was it was damned impressive.

 

 

The 95-96 winter arrived same time as low solar cycle, that could have had an effect. Indeed we entered into a very dry blocked Atlantic pattern since March 95. We've been in a blocked set up since December.. 

Patterns of colder winters coming in the midst of dry blocked periods.. winters 08-12.. peaking 2010 very dry.. winter 05-06 though not especially cold also in the midst of a dry blocked theme since Feb 05 through to October 06. 

I've noted numerous sudden switches from very wet to dry colder winters in recent years..

95-96 on the back of very wet 94-95.

00-01 a colder Jan-March period on the back of exceptionally wet Autumn and December..

05-06 on the back of wet 04-05 winter.. indeed switch in Feb after very wet Jan notable.. a la Feb-Mar 95 switch.

08-09 switch from wet summer 07 through to summer 08..

09-10 switch very wet Nov 09 to very cold and dry..

12-13 switch from very wet April-Aug..

Mini switch 15-16 after very wet Dec it did turn into a dry latter half winter not cold though..

20-21 relatively cold dry winter in north at least after the deluge of winter 19-20...

Edited September 8, 2021 by damianslaw

[summer blizzard]

Interesting output tonight and not potentially as warm as we have seen.

GEM is much more aggressive with the Atlantic, Euro and GFS build pressure somewhere near Scandinavia.

[sebastiaan1973]

Glosea5 is not so good. High pressure at the Atlantic Ocean. Perhaps some PM-air. Once again the sea water west of the northern part of North-America is warm.

https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean

[damianslaw]

Stopped looking at long range forecasts a long time ago. Not without interest, but prone to high margins of error. The above pressure pattern anomaly is the default winter pattern, no surprise then to see such display on offer. 

[northwestsnow]

Glossea at face value looks meh ! But might offer scope for nwlys which might favour elevated NW UK...

Next update will be fascinating ,just a nudge North of that HP in the Atlantic that would be grand.

[Don]

Those who are enjoying this warm September but want a cold winter had better hope for some much cooler weather in the second half of the month (not looking likely with the current model output) as Gavin Partridge has done some analysis in his winter update today and the overall signal for warm Septembers is bad news if you want a cold winter to follow!  

Edited September 12, 2021 by Don

[Seasonal Trim]

27 minutes ago, Don said:

Those who are enjoying this warm September but want a cold winter had better hope for some much cooler weather in the second half of the month (not looking likely with the current model output) as Gavin Partridge has done some analysis in his winter update today and the overall signal for warm Septembers is bad news if you want a cold winter to follow!  

I wouldn't worry too much about what Gav said. We're very much in uncharted territory with this Septs CET which could end up much higher than the analogues that Gav was using in his vids.

Who knows what might happen if the CET ands up above 17c.

[Don]

1 minute ago, Seasonal Trim said:

I wouldn't worry too much about what Gav said. We're very much in uncharted territory with this Septs CET which could end up much higher than the analogues that Gav was using in his vids.

Who knows what might happen if the CET ands up above 17c.

A winter month with a 10C+ CET?!   I hope these words don't come back to haunt me in a few months! 

[Dorsetbred]

12 minutes ago, Don said:

A winter month with a 10C+ CET?!   I hope these words don't come back to haunt me in a few months! 

Uncharted waters, so who knows what will transpire.. a point of note, the sea temperature in Bournemouth is 0.8C ABOVE the long term average currently..

[Seasonal Trim]

51 minutes ago, Don said:

A winter month with a 10C+ CET?!   I hope these words don't come back to haunt me in a few months! 

I'd move too Iceland if our Winters were that bad!

Edited September 12, 2021 by Seasonal Trim

[Cheshire Freeze]

Much of a muchness from GLOSEA in terms of the advertised winter pattern. Pretty much a full house of seasonals now with a general pattern of LP to the N and HP to the S.

They all feature that HP anomaly in the NE Pacific too as a result of well above average SSTs in that area. 

[sebastiaan1973]

There is still room for improvement. And, seasonal models are not very good suited for SSWs. 

[Don]

3 hours ago, CreweCold said:

Much of a muchness from GLOSEA in terms of the advertised winter pattern. Pretty much a full house of seasonals now with a general pattern of LP to the N and HP to the S.

They all feature that HP anomaly in the NE Pacific too as a result of well above average SSTs in that area. 

I get the impression you are becoming less optimistic for the winter CC?  However, those above average SST's in the NE Pacific have moderated a bit this last week and hopefully this will continue.  We will have to see!

[northwestsnow]

Farmers Almanac  going for a mild and stormy Canadian winter.....

[bluearmy]

The latest copernicus data which shows all the winter lrf’s has a jan neg AO sig for jan from a few models. It’s not a disaster for coldies just yet !  (Of course long rangers always have bucket loads of salt anyway ) 

[jules216]

The ensemble mean color shading are so misleading I mean the orange is like 1hPa higher then mean,hardly screams fat blocking high with would equal like 20hPa Higher then mean, throw in the spread and it doesnt mean "lemon"

[SqueakheartLW]

This is becoming a consistent theme in these 60N zonal wind charts on weather is cool.

After an initial period of stronger than average early polar vortex there is a general trend showing here for things to go weaker than average as we get to the end of the month.

More importantly I also keep seeing a trend to a very weak jet stream too with those blue anomalies showing up quite a lot. Either shows a very weak jet stream , the jet is displaced north or south of 60N a lot or a meandering jet stream which would cancel out the zonal signal anyhow.

Far too early in the season for snow unless something freakish happens but it would be better to see these signals 2 months later on rather than now.

[damianslaw]

57 minutes ago, SqueakheartLW said:

This is becoming a consistent theme in these 60N zonal wind charts on weather is cool.

After an initial period of stronger than average early polar vortex there is a general trend showing here for things to go weaker than average as we get to the end of the month.

More importantly I also keep seeing a trend to a very weak jet stream too with those blue anomalies showing up quite a lot. Either shows a very weak jet stream , the jet is displaced north or south of 60N a lot or a meandering jet stream which would cancel out the zonal signal anyhow.

Far too early in the season for snow unless something freakish happens but it would be better to see these signals 2 months later on rather than now.

Jetstream pattern default position all year, very weak - resulting in lengthy dry periods, and shorter unsettled more trough/cyclonic conditions with propensity for low pressure to anchor itself to the south of the UK. Quite an unusual set up.. and notable for its persistance.. indeed in a couple of months time, it would be offering significant wintry potential.. alas its September.