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08-12-2020, 17:03   #16
Gonzo
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GFS parallel going for a more significant warming compared to the operational run, almost verging on SSW levels and the PV getting stretched and displaced towards Europe, looking good.



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08-12-2020, 17:13   #17
hatrickpatrick
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If we get a downward propagation and it's a relatively quick tropospheric response which is usually the case with splits, the straightforward answer is yes.
I think one of the reasons people are more cautious about this recently is because people remember the last time we had a major SSW resulting in a split vortex during December, only for it to downwell so ridiculously slowly that it was already Spring before any blocking occurred. This may have been early 2019?

Do we as yet know why that particular split took so long to make its way down to the troposphere, and whether we can predict that in advance based on teleconnections?
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08-12-2020, 17:16   #18
sryanbruen
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You didn't get that information and charts from GavsWeatherVids by any chance did ya Gonzo

But for real though, the developments right now in the works are very interesting from a stratospheric standpoint.

The prospects are for a series of minor wave-1 displacement events to occur through mid into late December before possibilities increase of a wave-2 split occurring in the New Year. I've seen some comparison between evolution of this and what happened in 2012-13 which was quite a blocked December in the higher latitudes and this eventually resulted in a major wave-1 displacement of the stratospheric polar vortex during the first few days of January 2013 before it was ripped apart by a wave-2 split through the second week of January.

Every event is unique however gives us an idea of what can happen and how events unfold.
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08-12-2020, 17:23   #19
sryanbruen
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I think one of the reasons people are more cautious about this recently is because people remember the last time we had a major SSW resulting in a split vortex during December, only for it to downwell so ridiculously slowly that it was already Spring before any blocking occurred. This may have been early 2019?

Do we as yet know why that particular split took so long to make its way down to the troposphere, and whether we can predict that in advance based on teleconnections?
That wasn't anything to do with the January 2019 major SSW event, that was from the annual final warming which somewhat unusually had the dynamic wave forcing of a mid-winter major SSW event and has been discussed by Lee and Butler in the link below. I quote:

Quote:
Final stratospheric warmings are radiatively driven as the sun returns to the Arctic pole, but can also be driven by dynamic wave forcing akin to a major SSW. The FSW in April 2019 had a substantial dynamic component, with high wave activity preceding the event. This developed an unusually intense Aleutian high which displaced the weakening SPV and produced date-record strong easterly U1060 in early May (a minimum of -20.4 m s-1 was reached on 4 May). Although the envelope of variability becomes smaller into the summer, U1060 remained close to date-record minima through June.
http://centaur.reading.ac.uk/87110/1...r_accepted.pdf

Unlike February 2018, the January 2019 major SSW event did not couple with tropospheric weather patterns to produce a negative NAO whilst the strong vortex event that occurred in February/March 2019 did produce a strongly positive NAO.

Last edited by sryanbruen; 08-12-2020 at 17:27.
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08-12-2020, 17:47   #20
nacho libre
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Speaking of Amy Butler, she seems confident of an SSW event sometimes in January. So along with glosea5 things do look very promising.
We just have to hope that if the Russian High is still on the scene, it does not turn out to be a spoiler- sometimes major warmings can actually flip a promising troposhere pattern, whereby we end up on the mild side of arctic air plunging south.
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08-12-2020, 17:54   #21
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[QUOTE=nacho libre;115552981
We just have to hope that if the Russian High is still on the scene, it does not turn out to be a spoiler- sometimes major warmings can actually flip a promising troposhere pattern, whereby we end up on the mild side of arctic air plunging south.[/QUOTE]

I think that's what happened in feb 09. A decent cold pattern during the first half of that month but a mild second half which I think was caused by a ssw which ruined the pattern.
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13-12-2020, 17:45   #22
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Can't show charts at the moment but looks like models now showing a more significant re-intensification of the stratospheric polar vortex in the short term following the very minor displacement.

However, despite the above, the trop and strat remain disconnected with one another.

As for longer term with prospects on the chances of a polar vortex split or a more significant warming, the CFSv2 has backed off that significantly. Looks to me that the ECM and the UKMO Glosea5 have fared the same with any ideas of such being pushed back to at least mid-January. This is a very long time away and when I mentioned it, it was a wild card.

To end on some good news - well if you're a stratosphere observer like me, seasonal stratospheric zonal wind forecasts have been added to the Copernicus site with the UKMO Glosea5 included.

https://twitter.com/SimonLeeWx/statu...519649281?s=20
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13-12-2020, 21:46   #23
nacho libre
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Not good news at all. I did note a recent UK Met Office up date hinting at something happening in Mid January. We just have to hope if there is a ssw in mid january that it downwells quickly. It would be just our luck to get a cold spell in Mid to late February.
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15-12-2020, 23:10   #24
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The extent of the blocking is impressive. Of course it probably won't happen like this, but if it did the vortex would be under pressure big time
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18-12-2020, 10:42   #25
sryanbruen
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Not good news at all. I did note a recent UK Met Office up date hinting at something happening in Mid January. We just have to hope if there is a ssw in mid january that it downwells quickly. It would be just our luck to get a cold spell in Mid to late February.
Been holding off on posting about the wave-1 warming that the GFS has been showing for a little bit for the last week of the year. This morning it has gone to the brim with a situation where a split would be inevitable in my opinion. However, that's only an interpretation from the 0z run, will we get to that extreme?

A fairly significant stratospheric warming is supported by the ensembles nevertheless. Remember that this is only an average of all perturbations, there would be ones that show a weaker warming but also ones that show a more intense warming.



Still no signal for a reversal just yet which is no surprise really with the hemispheric profile.



Reversal in the very upper strat shown on that run.

https://twitter.com/SimonLeeWx/statu...544013315?s=20

Last edited by sryanbruen; 18-12-2020 at 11:14.
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18-12-2020, 12:33   #26
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I see some strat' experts are indicating a SSW may occur just after the first week of January. I would love to know what the glosea5 model take on it is.
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18-12-2020, 13:02   #27
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Originally Posted by sryanbruen View Post
Been holding off on posting about the wave-1 warming that the GFS has been showing for a little bit for the last week of the year. This morning it has gone to the brim with a situation where a split would be inevitable in my opinion. However, that's only an interpretation from the 0z run, will we get to that extreme?

A fairly significant stratospheric warming is supported by the ensembles nevertheless. Remember that this is only an average of all perturbations, there would be ones that show a weaker warming but also ones that show a more intense warming.



Still no signal for a reversal just yet which is no surprise really with the hemispheric profile.



Reversal in the very upper strat shown on that run.

https://twitter.com/SimonLeeWx/statu...544013315?s=20
Sryanbruen, you fill us with so hope : )

If you look back to 2018 can you see any correlation between now and then, as in was it showing something similar a month or so pre split? Or is each lead time to an event different?
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18-12-2020, 17:25   #28
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The GFS 12z is showing the strat temperatures reaching 4c on the 30th, think I saw a similar chart either on the 6z or the 0z today. I'm not sure if we want an SSW though if the trop pattern the GFS has been showing on the last 3 runs happens.
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18-12-2020, 17:28   #29
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just about getting to a SSW on the latest GFS run:



By January 3rd the PV very much under strain and almost split.

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18-12-2020, 17:43   #30
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It would be ironic and just our luck if we got into a decent cold pattern which is possible from what the models are showing...........

.... and then for an ssw to change the pattern to something less cold. I think I'd cry......
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