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18-12-2020, 18:39   #31
sryanbruen
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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?
2018 was an absolute perfect evolution for a major SSW event in my eyes and getting high latitude blocking on our side of the globe with a severe cold easterly airflow. Only thing was the timing of it being in early February so the severity of the succeeding cold spell was limited somewhat by the time of year but still a truly exceptional period we had. The pattern being so extreme and blocked kind of played against us in a way as the high retrogressed over to North America and the negative NAO became western based. This allowed Storm Emma to successfully undercut the block and turn us relatively milder. So although eastern parts of the US was very mild when we were in the freezer, March and April would become extremely cold and snowy in the US. It's difficult to compare to that.

In late January 2018, we were seeing signs of a SSW event in deep Fantasy Island of the GFS operational run. At first closer to mid-January, this was looking like a minor wave-1 warming with the PV displaced from the pole which was a start as January had been an active month for the stratospheric polar vortex (SPV). I had fairly good confidence that something more notable would come from this closer to the timeframe as MJO phasing was looking good, heat flux was good etc. I made quite a bold statement on 25 January 2018 below:

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The question on our minds at the moment is that will the beast be unleashed in February 2018? When it comes to the bigger picture - i.e. my methodology I use to make my forecasts - it does look pretty compelling.

The significant stratosphere warming (again not a SSW though) is still up for grabs in early February on the GFS runs, see the latest 12z for example below. Even the ECM is showing some warming going on in the stratosphere (though only at 10hPa and not at 30hPa at all).

I will not put any bets (you should never do gambling on weather anyway) on the Beast From the East coming but what I can say is that something is certainly up in the air here.
I also remember closer to February, some GFS runs would show the SSW event much weaker. This was back when I looked at every single run regularly which I don't do as much nowadays. I had headaches from these flips and flops despite the overall trend being evident and forcing myself to have a break just to come back immediately because the GFS would show a "massive upgrade" on the warming and a big wave-2 split to occur around 12 February followed by an even bigger split around 17 February.

That bold statement verifying was all luck to be honest. The trop and strat could easily have not linked with one another or as in the case of Jan 2019, not project onto the NAO.

Split events tend to have quicker tropospheric responses than displacement events.

And has been posted above kindly by Gonzo, the latest GFS is indeed on the cusp of a split towards the end of its run. It does not quite have a reversal at 60N 10hPa (perhaps down to around 8hPa in the upper strat) but is on the verge of one. That is a fairly significant sudden stratospheric warming. It follows on from the 0z and to some extent the 06z too that looked prone to a SPV split. The 12z confirms my thoughts. If we were to get a major SSW event (zonal mean zonal winds at 60N 10hPa reversed to easterly), could be a big spanner for any seasonal forecasts which have already been poor for December.

As for Glosea5 nacho libre, it does not show a major SSW event but is in line with the ECM of showing a weaker than average vortex.

We shall see how it evolves but as I said in a prior post, before the longer range models backdated on the possibility of a major SSW event, this is the most excited I have been since 2017-18.

Last edited by sryanbruen; 18-12-2020 at 19:28.
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18-12-2020, 19:51   #32
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Great post Sryanbruem. Starting to get giddy myself.
Anothe question yoy dont gave to go into great detail with reply but was 1947 and 62/63 consideed as ssw events?
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18-12-2020, 21:52   #33
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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......
Yeah, that would be a real kick in the teeth if it happened. As Sryan mentioned if there is a SSW it will ask questions of long range models like Glosea5. Personally i'll be glad if they get it wrong, aside from the obvious reason, i don't like the idea of models being able to predict 3 months ahead. I know a lot of people will say this will never happen, but if it did a lot of the fun of model watching would be gone.
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19-12-2020, 11:50   #34
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Well this is interesting
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19-12-2020, 11:53   #35
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Well this is interesting
Its been pulled apart...good news.
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20-12-2020, 09:53   #36
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Great post Sryanbruem. Starting to get giddy myself.
Anothe question yoy dont gave to go into great detail with reply but was 1947 and 62/63 consideed as ssw events?
1947 predates stratospheric records in the 1950s unfortunately but has been part of many discussions before of how it became so severe and so suddenly from the second half of January as pressure rose initially from the south.

1962-63 had a Canadian Warming event in November which is another type of SSW event that occur mostly in Nov/Dec. These are similar to minor SSW events in that they are generally not associated with a reversal in zonal mean zonal winds at 60N 10hPa (with some exceptions like Nov 2000). This likely had some impact in displacing the Greenland lobe of the vortex allowing high pressure to build, helped by the fact there was the developments of a North Atlantic tripole which favours negative NAO. January 1963 did have a major SSW event which likely helped prolong the cold winter pattern into February.
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20-12-2020, 09:57   #37
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Well this is interesting
Yesterday, we saw the first GFS run with a reversal at 60N 10hPa although just barely at -1.0 m/s. This still constitutes as a major SSW event. The consistency from the GFS on this SSW event has been notable. It is still showing now with the prospects of the split in early January.

This is being driven by the forecast of possibly near or record breaking heat flux, and may occur at a similar time to the major SSW events of January 1985, January 2013 and January 2019.

Continues to look interesting in the stratosphere indeed. If (there's always ifs involved!) the strat were to follow with a quick tropospheric response for Europe, the upcoming seasonable period with a series of polar maritime NW'lies and N'lies will be more of a teaser if anything.
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20-12-2020, 10:50   #38
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Thoughts?

https://twitter.com/SimonLeeWx/statu...056972289?s=19
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20-12-2020, 18:04   #39
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the 12z has updated and is looking most interesting.

A fairly major warming by New Years Eve.



Another warming takes place between Newfoundland and Cork/Cornwall/Essex



January 3rd, Goodbye PV, looks like a fairly decent displacement and split.

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20-12-2020, 18:11   #40
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Mentioned it in above post

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Originally Posted by sryanbruen View Post
Yesterday, we saw the first GFS run with a reversal at 60N 10hPa although just barely at -1.0 m/s. This still constitutes as a major SSW event. The consistency from the GFS on this SSW event has been notable. It is still showing now with the prospects of the split in early January.

This is being driven by the forecast of possibly near or record breaking heat flux, and may occur at a similar time to the major SSW events of January 1985, January 2013 and January 2019.
We have now had the second GFS run that sees a major SSW event happening and the central date (day the reversal happens) being January 2nd. This run shows a bigger reversal than the previous one. In fact, as far as the run goes to t384, the 10hPa zonal mean zonal wind drops to -24.6 m/s at 60N on 5 January. That is a solid major SSW event if I ever saw one.

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20-12-2020, 19:01   #41
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What are your thought on these comments, Sryan:

"That was the big lesson taught by 2019's failed downward propagation. That SSW was huge, featuring some record-breaking vertical wave activity flux, but predominantly wave-1 driven.

In such a situation, it seems to be much less likely that the vertical structure of the stratosphere aligns in a way that permits rapid downward propagation.

Instead we're left looking for 'drip-down' of anomalously warm stratospheric temps to produce a negative NAM (i.e. negative AO in the troposphere), which tends to produce smaller-scale impacts that more easily miss the UK. It can also be stalled by an unreceptive troposphere, much as we saw in Jan-Feb 2019.

In a wave-2 dominated SSW, there's still no guarantee of the rapid downward propagation, but at least some slower propagation seems to be very likely and the resulting cold weather outbreaks tend to cover wider areas and persist for longer. Of course, the UK can still miss out, being such a narrow slither of the hemisphere."

Do you think this will be a wave 2 dominated SSW? Also, are you concerned
that the Glosea model isn't on board with this yet?
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20-12-2020, 19:33   #42
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What are your thought on these comments, Sryan:

"That was the big lesson taught by 2019's failed downward propagation. That SSW was huge, featuring some record-breaking vertical wave activity flux, but predominantly wave-1 driven.

In such a situation, it seems to be much less likely that the vertical structure of the stratosphere aligns in a way that permits rapid downward propagation.

Instead we're left looking for 'drip-down' of anomalously warm stratospheric temps to produce a negative NAM (i.e. negative AO in the troposphere), which tends to produce smaller-scale impacts that more easily miss the UK. It can also be stalled by an unreceptive troposphere, much as we saw in Jan-Feb 2019.

In a wave-2 dominated SSW, there's still no guarantee of the rapid downward propagation, but at least some slower propagation seems to be very likely and the resulting cold weather outbreaks tend to cover wider areas and persist for longer. Of course, the UK can still miss out, being such a narrow slither of the
hemisphere."

Do you think this will be a wave 2 dominated SSW? Also, are you concerned
that the Glosea model isn't on board with this yet?
All good and fair points brought forward by that Netweather poster. Difficult to say personally until we get into the event itself but GFS seems to suggest a wave-2 split of some kind from my amateur observation though this needs to become a trend (only the second GFS run to show a reversal for instance).

No, I am not overly concerned that the Glosea5 isn't on board with the idea of a major SSW event. Models playing catch up can come at short notice, just look at the ECM this evening for the weekend of the 26th/27th - not saying it will though the GFS consistency as of late has been noteworthy.

Just a reminder of what made 2019 different in comparison to Jan 2009, Jan 2013 and Feb 2018.

https://twitter.com/SimonLeeWx/statu...053041664?s=20
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20-12-2020, 23:52   #43
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18z is another reversal and wave-2 split. In fact, a very notable split. One of the most beautiful charts I have seen - still not quite February 2018 beautiful in my opinion though but up there most definitely.
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21-12-2020, 11:46   #44
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0z showed a major SSW event (reversal) again but 06z shows zilch though a significant warming regardless. Shows it's still up in the air rather than totally certain, we're still talking about quite deep FI here.
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21-12-2020, 11:52   #45
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0z showed a major SSW event (reversal) again but 06z shows zilch though a significant warming regardless. Shows it's still up in the air rather than totally certain, we're still talking about quite deep FI here.
What are we talking about here is it a storm or what
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