Stratosphere and Polar Vortex Watch 2020

[mushymanrob]

can somebody explain wave 1 and wave 2 forcing please? or point me in the right direction if theres something on it... cheers..

 

[Kirkcaldy Weather]

 

[sebastiaan1973]

 

[Don]

18 minutes ago, sebastiaan1973 said:

 

Not sure what this means moving forward?

[DOdo]

35 minutes ago, Don said:

Not sure what this means moving forward?

Hi Don if you look at his tweet He explains what he means

[Don]

25 minutes ago, DOdo said:

Hi Don if you look at his tweet He explains what he means

Thanks DOdo 

An increased risk of colder weather later on then.

[Mike Poole]

We have our first reversal of the winter, GEM 0z ensemble 2:

Baby steps...

[sebastiaan1973]

Once again an EC46 predicting a slowly decline of the winds at 10 hPa.

http://apps.ecmwf.int//webapps/opencharts/favicon.ico ECMWF | Charts

APPS.ECMWF.INT

Edited December 3, 2020 by sebastiaan1973

[Shuttler]

I don't want to be a spoiler here but I think the chances of a split SSW this winter are LOW. It really is only the split SSW that has the power to override the inherently mild Arctic Sea Ice signal this winter and give us the HLB and -NAO most people crave for. A displaced SSW rarely delivers sig cold for Europe and can actually enhance the westerlies in many cases.  My reasoning;

1. wQBO + low solar combo is not ideal. When looking back a split SSW occurred 3 times in the 15 winters that combination was in place in the last 60 years. Giving a roughly 1 in 5 or 20% chance.

2. However, we are at risk of transitioning to a eQBO before the end of the winter, such are the pecularities of the QBO these days. But, looking back we really need to be 'entrenched' in that eQBO phase well before the winter to give max attack on the PV. Most eQBO split SSWs had transitioned into the eQBO phase by at least the summer before.

3. Aleutian low + Scandi block is the ideal combo for wave breaking and Strat disruption. But, approx 10th Dec onwards we're moving back to the negativePDO/La Nina base state with Aleutian blocking/high pressure, and in 2-3 weeks time the Barents-Urals block is also likely to weaken (latest ECM46 confirms both). 

4. There is no sign of a very active MJO phase, just weak and Phase 4/5 next couple of weeks (maritime continent). Again, a precursor to a split SSW event is often a very active MJO wave running from Phase 2/3 thru to 7.

So I have an inherently mild winter in Europe with any cold largely limited to NW'ly polar interludes rather than any beast from the east type stuff. But, I could easily be proved wrong. 

[Catacol]

7 hours ago, Shuttler said:

I don't want to be a spoiler here but I think the chances of a split SSW this winter are LOW. It really is only the split SSW that has the power to override the inherently mild Arctic Sea Ice signal this winter and give us the HLB and -NAO most people crave for. A displaced SSW rarely delivers sig cold for Europe and can actually enhance the westerlies in many cases.  My reasoning;

1. wQBO + low solar combo is not ideal. When looking back a split SSW occurred 3 times in the 15 winters that combination was in place in the last 60 years. Giving a roughly 1 in 5 or 20% chance.

2. However, we are at risk of transitioning to a eQBO before the end of the winter, such are the pecularities of the QBO these days. But, looking back we really need to be 'entrenched' in that eQBO phase well before the winter to give max attack on the PV. Most eQBO split SSWs had transitioned into the eQBO phase by at least the summer before.

3. Aleutian low + Scandi block is the ideal combo for wave breaking and Strat disruption. But, approx 10th Dec onwards we're moving back to the negativePDO/La Nina base state with Aleutian blocking/high pressure, and in 2-3 weeks time the Barents-Urals block is also likely to weaken (latest ECM46 confirms both). 

4. There is no sign of a very active MJO phase, just weak and Phase 4/5 next couple of weeks (maritime continent). Again, a precursor to a split SSW event is often a very active MJO wave running from Phase 2/3 thru to 7.

So I have an inherently mild winter in Europe with any cold largely limited to NW'ly polar interludes rather than any beast from the east type stuff. But, I could easily be proved wrong. 

Maybe....but I'll question the stats here. 50% of Nina/wQBO years have produced a SSW. The MJO is not weak - dont be fooled by the RMM plots. There is no sign yet of the GWO slipping back steeply into a Nina context (though it is possible it might in time) and actually ENSO 3.4 is back up to -1.0 now. And is this really a classic Nina chart hemispheric pattern? Not over the US and not over the atlantic for mid December.

And where is the Ural high degradation? Not into early Jan....

 

 

Edited December 4, 2020 by Catacol

[damianslaw]

Just getting a sense expected patterns for this winter may not come to fruition, I say may, but won't. What was expected in November was a bust, non-La Nina pattern, currently same, and no obvious sign of a change. 

[Cheshire Freeze]

1 minute ago, damianslaw said:

Just getting a sense expected patterns for this winter may not come to fruition, I say may, but won't. What was expected in November was a bust, non-La Nina pattern, currently same, and no obvious sign of a change. 

Which calls into question the seasonal; modelling which has shown a traditional Nina pattern to this point. 

Wondering what the December update for the ECM seasonal Jan-Mar period will look like.

[chionomaniac]

22 hours ago, Shuttler said:

I don't want to be a spoiler here but I think the chances of a split SSW this winter are LOW. It really is only the split SSW that has the power to override the inherently mild Arctic Sea Ice signal this winter and give us the HLB and -NAO most people crave for. A displaced SSW rarely delivers sig cold for Europe and can actually enhance the westerlies in many cases.  My reasoning;

1. wQBO + low solar combo is not ideal. When looking back a split SSW occurred 3 times in the 15 winters that combination was in place in the last 60 years. Giving a roughly 1 in 5 or 20% chance.

2. However, we are at risk of transitioning to a eQBO before the end of the winter, such are the pecularities of the QBO these days. But, looking back we really need to be 'entrenched' in that eQBO phase well before the winter to give max attack on the PV. Most eQBO split SSWs had transitioned into the eQBO phase by at least the summer before.

3. Aleutian low + Scandi block is the ideal combo for wave breaking and Strat disruption. But, approx 10th Dec onwards we're moving back to the negativePDO/La Nina base state with Aleutian blocking/high pressure, and in 2-3 weeks time the Barents-Urals block is also likely to weaken (latest ECM46 confirms both). 

4. There is no sign of a very active MJO phase, just weak and Phase 4/5 next couple of weeks (maritime continent). Again, a precursor to a split SSW event is often a very active MJO wave running from Phase 2/3 thru to 7.

So I have an inherently mild winter in Europe with any cold largely limited to NW'ly polar interludes rather than any beast from the east type stuff. But, I could easily be proved wrong. 

I agree with you entirely on displacement SSWs. Wave 1 events are useful though, by weakening the vortex and increasing the susceptibility to collapse from wave 2 activity.

I remember the first year that I started the strat threads - I certainly wasn’t expecting an SSW that year, but lo behold we had the biggest split that we have ever witnessed in the strat!

And the background that year, wQBO, weak Nina and increasing solar activity following solar minimum. I think that we will see significant wave activity into January and would not be surprised to see another whopping split SSW this year. The disconnect between the strat and trop is not unusual at this time of year, it often takes a bit of time, but if we enter a period of VI then the strat will take some breaking. Luckily the forecast wave 1 event is coming just in time to prevent that from happening 

[summer blizzard]

SSW's happen in wqbo years but not often with a standard deviation above +1 (only 09 I think) so I'm not sold on a technical ssw.

[bluearmy]

1 hour ago, chionomaniac said:

I agree with you entirely on displacement SSWs. Wave 1 events are useful though, by weakening the vortex and increasing the susceptibility to collapse from wave 2 activity.

I remember the first year that I started the strat threads - I certainly wasn’t expecting an SSW that year, but lo behold we had the biggest split that we have ever witnessed in the strat!

And the background that year, wQBO, weak Nina and increasing solar activity following solar minimum. I think that we will see significant wave activity into January and would not be surprised to see another whopping split SSW this year. The disconnect between the strat and trop is not unusual at this time of year, it often takes a bit of time, but if we enter a period of VI then the strat will take some breaking. Luckily the forecast wave 1 event is coming just in time to prevent that from happening 

Good to see you back ed .....

 I wondered if the forecasts high up would encourage your appearance! 

[Singularity]

4 hours ago, summer blizzard said:

SSW's happen in wqbo years but not often with a standard deviation above +1 (only 09 I think) so I'm not sold on a technical ssw.

I'm not sure whether we can classify the QBO in the usual manner this time around, though - as you know, it's been behaving peculiarly this year.

I've devised a measure to illustrate just how peculiar:

Here we see that the easterly phase was basically skipped out, the QBO cycling back to westerly descending in a little under half the usual time.

The vertical structure is also strange, akin to the mid-stages of the westerly phase but with the westerlies occupying a shallower height range than usual.

The big question, which I'm unsure of the answer to, is how this affects the Brewer-Dobson transport of ozone from the tropical to polar stratosphere. Does a shallower westerly layer mean a bit more ozone makes it through, or is it more of a 'shutting the door' mechanism - any westerly layer will do?

In any case, while it's a shame to miss out on the 'ultimate' combo of eQBO and 1-2 years past solar minimum this winter (we'll probably have another shot next winter...!), the QBO is not a dominant factor in SSW likelihood, more a regulator. Usually in a moderate La Nina event, it would be combining with minimal high-frequency tropical cycling (MJO, Kelvin waves and the like) to enhance restriction of the poleward extension of the beefed up subtropical highs. This Nov-Dec has, at least so far, been proving different, for reasons that warrant further research but probably include the widespread anomalous warmth in the subtropical and non-tropical North Pacific Ocean. The Nina forcing may be getting seriously distorted, even swamped out, by something resembling Nino forcing.

Fascinating, but also worrying when you consider what a predominance of the Nino state would mean for some regions - repeating tendency toward the same anomalous weather, be that warm or cold, wet or dry.

[Catacol]

5 hours ago, summer blizzard said:

SSW's happen in wqbo years but not often with a standard deviation above +1 (only 09 I think) so I'm not sold on a technical ssw.

 

[chionomaniac]

Agree with you @Singularity. The QBO hasn’t behaved ‘normally’ for a while now, so rather than being reliable in expected trop outcomes it is now another wild card. Years ago, one could match teleconnections to expected trop H500 anomaly plots. With the warming arctic and unreliable QBO, I no longer think that this is the case - though MJO/GWO plots do have some merit. 

Edited December 5, 2020 by chionomaniac

[feb1991blizzard]

Just wondering, wasn't the 6th Jan 2013 event a wave 1 event, initially a displacement but then the complete disintegration of the SPV for the rest of the winter ensued thus gave further episodes of blocking almost every 2 weeks like clockwork until late March?

[Catacol]

Hmmm - too far out for dancing....but good to see nonetheless....

Wave 1 forcing encouraging a split up as high as 30hpa and all layers below. Baby steps.....

 

[northwestsnow]

4 minutes ago, Catacol said:

Hmmm - too far out for dancing....but good to see nonetheless....

Wave 1 forcing encouraging a split up as high as 30hpa and all layers below. Baby steps.....

 

Back end of GFS6Z..

[bluearmy]

3 minutes ago, Catacol said:

Hmmm - too far out for dancing....but good to see nonetheless....

Wave 1 forcing encouraging a split up as high as 30hpa and all layers below. Baby steps.....

 

No sign of this on the ecm op at day 10 .......that’s the next check on this which has been showing consistently on the gfs runs  (and also shows on the gefs as mean feature at day 10) 

[Allseasons-Si]

 

[Scott Ingham]

1 minute ago, Allseasons-si said:

 

Hmm..... bang on cue for me this!!!! Starting to get a little excited

[Allseasons-Si]

Just now, Scott Ingham said:

Hmm..... bang on cue for me this!!!! Starting to get a little excited

It is the gefs though and is fraught with danger,seen this happen many times and then drop it

we need the ECM showing this but only goes out to day ten.