Stratosphere watch 2023-24

Gonzo

https://www.boards.ie/discussion/comment/121619434#Comment_121619434

never again am I spending 3 weeks going after cold and snow potential only for it to end up a busted flush from a snow perspective. If the models aren't modeling some sort of decent easterly in the next cold spell I won't be putting nearly as much time into it.

All we can do is hope that this reversal leads to something half decent even if it's just for a few days.

nacho libre

https://www.boards.ie/discussion/comment/121619563#Comment_121619563

I hope you're right but even an overall weak pv as we see can wreck blocking. It's remarkable that the pv has never really got going this year.

I just won't be believing any charts that show a snowy cold outbreak until its stil showing at 2 or 3 days out. The 2018 cold outbreak was counted down seamlessly. If only all cold spells could be like that instead of all the wobbles. Some people like that aspect of it, but it's not for me .

Gonzo

https://www.boards.ie/discussion/comment/121619673#Comment_121619673

I've had enough wobbles and busts for the year so if we get another shot in February I want it to be the real deal without the twists and turns. IF we can't get that i'd settle for a month of high pressure/ dry weather without feeling let down.

bazlers

Yes once bitten twice shy when it comes to cold chases. We have more bies than if you slept in a den of mozzies! (Im sure they sleep in dens 🤔)

sryanbruen

So today is the day that we possibly see the most non-major technical major sudden stratospheric warming on record declared, wow that's a mouthful but if I ever seen an event undeserving of being called "major", this would be it.

We have a very small window of reversal for the next 12 hours or so and for this event to be designated, the daily mean value needs to be under 0 m/s as previously stated. GFS showed the reversal happening from 06z on Tuesday so it should be designated if it holds.

This "major" SSW is actually aiding in the disappearance of -NAO via downward wave reflection, according to Simon Lee and I'll allow him to explain. Figure via Weatheriscool.

It's possible that the criteria for a major sudden stratospheric warming (SSW) will be marginally reached on Tuesday 16 January (daily-mean 10 hPa 60°N zonal-mean winds reversing to easterlies).

However, this event doesn't come with the usual fanfare of an SSW...

The stratospheric polar vortex has been weak (negative NAM) since the start of 2024, when a minor stratospheric warming occurred (no U10 hPa 60°N wind reversal).

This has already coupled with the troposphere, associated with the current Greenland Blocking/negative NAO regime.

What is expected to happen over the next few days actually seems to be the "end" of the weak vortex, which is not typical for a major SSW.

Upward wave activity immediately becomes unusually low or even negative (reflection), allowing the vortex to begin recovering radiatively.

In fact, the expected acceleration of the vortex winds (at 10 hPa) after the reversal is remarkably dramatic -- back up to *above normal* strength in one week. That's almost as dramatic as the deceleration that would normally occur in a major SSW!

All-in-all, this "major" warming (if you can call it that!) does not appear to have any of the average characteristics of a major SSW. It is a fascinatingly odd event, but it does not appear to be a harbinger of an extended disrupted vortex & negative NAO -- perhaps the opposite.

What a peculiar "event" but a very frustrating one for coldies I'm sure to read!

nacho libre

https://www.boards.ie/discussion/comment/121627081#Comment_121627081

Well based off that I don't see how we are going to have a hlb to dominate much of February. The other drivers may lead to a high nearby but I can't seen it being able to extend far enough north

So I fear when the UKMO talk of lower chance of milder and unsettled weather that will change to us all going milder. I can see a sudden flip in the likes of Glosea and the ec46 to a less blocked outcome, especially if it was predicated on the idea of a true major ssw happening with the dramatic effects it can have on the trop.

Mr Bumble

According to this chap, we had a weak and brief wind reversal in the stratosphere a few days ago with potential for impact in a few weeks. He does mention a "warm outcome" for us.

https://www.youtube.com/watch?v=a7DdYaOtOLI

sryanbruen

https://www.boards.ie/discussion/comment/121647667#Comment_121647667

We have already seen the impact if Simon Lee's explanation two posts above is to be believed and any "warm outcome" is unlikely to be directly related to this very very weak major sudden stratospheric warming (likely the weakest of all-time).

We can see the radiative strengthening of the stratospheric polar vortex aloft using the NAM forecast below (the blue colours top left indicating +NAM or similar to positive Arctic Oscillation conditions). This is a normal procedure following major sudden stratospheric warming events, particularly in early and mid-winter when there's still plenty of time for radiative cooling.

Very positive AO surface conditions expected for at least a week before a more muted signal appears with rather neutral conditions though still leaning on the slightly positive side. An indication of low pressure not moving anywhere fast away from the North Pole and blocking is more difficult to develop with such conditions.

All those seasonal models showing a very blocked February in the high latitudes not looking good right now.

nacho libre

https://www.boards.ie/discussion/comment/121647828#Comment_121647828

Yeah. The same seasonal models that predicted a great summer in 2023. There is a lot of noise about why this SSW might not deliver, but the simple explanation is we need more than a weak reversal that barely lasts 24 hours. As you said it's only a major ssw in name.

This is why I am very sceptical of any high getting far enough north to deliver snowy cold. I am just hoping we stay settled and don't see a sudden flip to an unsettled outlook for much of February.

sryanbruen

https://www.boards.ie/discussion/comment/121647937#Comment_121647937

Just looked back through the C3S MSLP anomalies for the summer months over various monthly updates (March-June) and I don't see any particular strong signal on the mean from any of them for the summer. Neither indicating a great or terrible summer. Of course you will see better signals in individual models but I tend to use the mean when viewing these models.

Meanwhile, the February blocking signal goes back many many months and has been evident in every single update of the C3S suite means. This would be a massive bust.

Fail to see how this will come off unless we see a 180 swing in the model output with that vortex parked over Greenland which can well happen but...

nacho libre

I thought Glosea and some of the other Seasonal were going for a very dry July, but maybe I am wrong about that . Although maybe as you say looking at them individually can be deceptive. I think now the Scandi High option is a bust, I just don't see how we can get a high to the north west with a strong pv. Also given the vortex was in a weak state before the recovery in zonal winds we could see a quick response to that. Is there any sign of a Ural high in FI to promote further wave 2 warming?

sryanbruen

So a long overdue update on the stratospheric front.

We got the technical major SSW criteria achieved on 16th January 2024, it lasted for over 36 hours and was among the closest, weakest examples of such on record. This is shown by the pink line (GEOS reanalysed data) just touching under 0 m/s in mid-January on the chart below.

Wave reflection from this meant the stratospheric polar vortex regained strength and the split brought about the minor SSW on 5th January was a distant memory. GEFS showing a possibility of some positive heights downwelling next week which could explain some of the weak high latitude ridging on some output and the -AO going back to negative.

Further ahead, we could be seeing a renewed reduction of the U-60N. Yes we're getting to the time of year where they weaken naturally but talking weaker than average. There is not much sign of this on the EC46 output but some GFS runs have been getting to technical major SSW at the end just past 360 hours. Note the uncanny similar timing to last year's major SSW 🤔

So might we be setting up a blocked March.. is anyone surprised at this? Because I am not, at all. Besides, despite the March snow last year, we haven't had a cold March since 2018.

sryanbruen

06z went a bit nuts with the major SSW.. bank if nothing else.

sryanbruen

GEFS 0z mean was in favour of major SSW. Some perturbations getting to record-breaking weak. EC46 currently still not showing interest but continuing to strengthen the reduction (if that makes any sense).

nacho libre

If we do get a ssw I hope it doesn't end up scuppering any cold spell later in the month. I see the UKMO are talking about snowy cold into early March

sryanbruen

Right now it looks more of a displacement rather than a split to me and unlikely to be wave reflection compared to the mid-January faux major SSW.

GEFS flip flopping as you'd expect given the timeframe but majority continue to favour a major event.

EC46 has gone more bullish on weakening but still not favouring a major event.

sryanbruen

First EC46 run showing reversal for this coming possible SSW. 81% of the GEFS 12z showing a major event.

Billcarson

It would be bloody typical if we get a major ssw later this month. You couldn't make it up. Just adds to my frustration with our weather these days. Im getting so p##sed off with our winters in particular at this stage that I look forward to some gentle spring warmth. A major ssw could put spring on hold and we get decent cold synoptics when it's too late. Just can't seem to win.

pad199207

https://www.boards.ie/discussion/comment/121731656#Comment_121731656

Exactly. We get the weather we want when we don’t want it.

sryanbruen

GFS 12z is first run to show a massive SPV split. It shows it both at 10hPa and 30hPa. A change on its recent runs showing a displacement type.

nacho libre

https://www.boards.ie/discussion/comment/121735697#Comment_121735697

If it happens could it be up there with the 2018 event?

Gonzo

https://www.boards.ie/discussion/comment/121736080#Comment_121736080

I reckon that ship has sailed already, the 2018 event happened final week of January I think and we're now into the second week of February.

Thewife

If you are referring to the BFTE that was end of February/early March I’m sure

nacho libre

https://www.boards.ie/discussion/comment/121737604#Comment_121737604

He is referring to when the SSW took place. He is saying the SSW this time will be too late,but the difference is there maybe a very quick response to it. If it occurs then we could have a cold start to spring

Gonzo

https://www.boards.ie/discussion/comment/121737615#Comment_121737615

Yeah the SSW in 2018 took place final week of January 2018 and it took effect just after mid February and we went into that BFTE final few days of February and Storm Emma first few days of March. We are 2 weeks later currently and the split if it happens won't happen for another few days/week so probably early March before we see any effects and we are into Spring by then.

sryanbruen

https://www.boards.ie/discussion/comment/121737586#Comment_121737586

It occurred second week of February Gonzo, the central date (first date of reversal) was February 12th. Nowhere near the final week of January. Where did you get that idea from? We seen effect 9-10 days later from February 21st/22nd when the blocking developed to our east but we wouldn't see widespread snow until later on the 27th.

But anyway @nacho libre that GFS 12Z would lead to a blocked start to spring at a similar timing to last year if we were to see downwelling. Every event is unique, just because 2018 produced the BFTE doesn't mean if we see a repeat of that beautiful SSW, we will see the same again. If you want a direct comparison between the two SSWs, it doesn't get to the levels of reversal of 2018 as 2018 seen a massive wave-2 with a second massive ridge near Greenland after the initial Siberian ridge. The 18Z continued with the same theme. The 0Z just about splits and is not nearly as huge.

sryanbruen

GFS 12Z back to showing that split evolution again. 94% of the ensemble suite showing a major event occurring by the 22nd February.

WolfeEire

https://www.boards.ie/discussion/comment/121741173#Comment_121741173

March is the new January. Thanks for the updates, @sryanbruen

sryanbruen

GEFS 0z was significantly different to any run in the past few days. Look how much more positive the ensemble mean for U-60N is (the blue line) compared to recent day 0z runs. As a result, there has been a big decrease in perturbations showing reversal but still at least 61%. Run to run variation is to be expected but this significant? Hmm.

sryanbruen

Very good analysis by bluearmy based on the 0z and 6z runs this morning here.

Basically there is a brief SPV split in the lower strat but it quickly merges the two vortices back together right over northern Europe which would be a recipe for an enhanced westerly flow in line with what some of the modelling have been showing. Possible complication that a wedge could lead to a southerly track of the jet stream after any systems would clear through but Iberian heights would probably continue.