Stratosphere watch 2023-24

sryanbruen

EC46 is the most bullish so far to suggest a big dip/deceleration in U-60N. This is a change from its recent trend towards less and less perturbations getting to reverse levels.

The most recent available ECM operational run only goes out to 29th December and at that point is showing a rather minor wave-1 warming over Siberia displacing the SPV towards eastern Europe. Besides that, there's not much else you can delve from this chart alone. Would need more frames but my best guess would be the possibility of a technical reversal of the U-60N through the first into the second week of January followed by a rather quick recovery as it would probably be a displacement event with how it looks here at t240.

The interesting part is where it is displaced. If it's displaced towards Scandi, that would open the doors for some very significant Atlantic ridging possibly if not sustained provided there would be downwelling. If a more major warming were to occur, the SSW would likely get displaced back to the North Atlantic which is not as interesting but also opens the door to the possibility of a split as the SPV would be more prone to getting stretched.

The medium range GEFS has seemed to have sort itself out after showing a poor trend the past week with an acceleration likely in U-60N through the final few days of December as the SPV returns temporarily to the North Pole after the recent displacement towards Europe. This is then succeeded by a deceleration through early January. Most keeping it within the 10-25m/s range as far out as they go on this latest 18z run.

I would mention the fact the GFS looks quite "meh" on the wave-2 amplitude front to give sufficient planetary wave activity to evolve into a split but the data we have to hand from Stratobserve... well.. the GFS goes the complete opposite to most of the modelling. Look at how cold it keeps the average stratosphere temperature for 60-90N 10hPa whilst the rest of the output warms things up. Laughable. Simultaneously as you'd expect this translates to an intensification in U-60N which is also the opposite to what the rest of the modelling goes for minus some minority ensemble members.

Some interest (food for thought if nothing else) shared by the World Climate Service. Using the top 10 analogs that had similar polar cap heights to the EC46 initialised on the 19th December, 8/10 of them seen a major SSW occur.

I'm pretty torn to be honest. More runs needed.

sryanbruen

https://www.boards.ie/discussion/comment/121505740#Comment_121505740

Boom!

https://twitter.com/AnnBruen/status/1737769641764622635

sryanbruen

Everything remains the same, nothing has changed as of the most recent post.

Only thing I'll update on is the GFS 12z is the first run that I've seen an evolution that would hint at the possibility of a split but it's at the very end. See where I've marked, you can see a second lobe over NA but note the absence of a secondary ridge.

The GFS continues to be different to the rest of the models with a slower progression and colder stratosphere.

WolfeEire

Like a knife through hot bitter hopefully.

sryanbruen

There we have an official split at the very end of the GFS 0z this morning. Merry Christmas, ho ho ho!

Kermit.de.frog

This currently looks like it could be more of a displacement event rather than an actual PV split. I'm looking forward to seeing how it evolves. Regardless the odds of much colder weather being ejected from the Polar latitudes is increasing. Will we be in the firing line? 😁

Happy Christmas everyone and to Syranbruen for superb work keeping this thread updated 🎅

sryanbruen

It's Christmas Day but I couldn't resist archiving this one from the latest GFS 06z.

It goes onto produce an absolute beast of a major SSW. A major wave-1 split with a reversal of -24.3 m/s at the very end. This is getting to the top percentile of major SSW events.

Fantasy land but it must be mentioned that both the GEFS and EPS are in favour of a strong wave-2 driven pattern which would split the vortex come the second week of January.

Anyway, I just wanted to bank this as it's a rare beauty. Merry Christmas to you all and enjoy the rest of your day best you can in spite of this mediocre weather!

nacho libre

https://www.boards.ie/discussion/comment/121535116#Comment_121535116

Go on Sryan! That's what we like to see. Did you say you can hear the rumblings of a siberian express in the distance?:)

Dazler97

https://www.boards.ie/discussion/comment/121535116#Comment_121535116

That's a northerly isn't it ?

Mount Vesuvius

Fire in the Stratosphere .

Massive signal now. Too big to ignore.

Models will reflect this soon.

sryanbruen

https://www.boards.ie/discussion/comment/121535727#Comment_121535727

No, this is the stratosphere watch thread. Please see the first post of the thread for in-depth explanation on how the stratosphere affects our tropospheric weather patterns.

Where the troughs (lows) and ridges (highs) are placed in the stratosphere is not necessarily where they'll be in the troposphere but they do tend to feed off one another to drive the weather.

I still think we're not any closer to seeing the extent this stratospheric warming will go. There is no consistency in the GFS operational runs. 0z showed a wave-1 displacement with the U-60N just barely reversing briefly to easterly. 06z not looking like it'll have any reversal though does split the SPV. Whether it's a technical major SSW (reversal) or not won't matter in the grand scheme of things unless it's a massive event like the GFS 06z OP plugged yesterday. All it means is it won't be classified as a major if so.

Mount Vesuvius

Zonal mean winds around the 8th Jan will be interesting. Hopefully we see a reversal for added effect to a Stratospheric PV that's not too healthy for maximum potential.

nacho libre

The lack of consistency from the GFS is annoying. If we do get a SSW we have to hope the effects of it downwell into the trop', otherwise the SSW won't be of much use really .

Mount Vesuvius

Well a split would have an impact and I think current PV lobe suggestions are in our favour of where the vortices go.

We watch and wait. Enjoy the rest of the holidays and come Jan 1st we should have a better idea of what is happening.

sryanbruen

Big steps back today from the EPS and GEFS with regards to a major SSW (reversal). Just a quarter showing reversal now on the EPS.

71% of the ensemble suite showed reversal yesterday...

https://twitter.com/RaleighWx/status/1739737310273343778

sryanbruen

EC46 on the other hand has finally gone to reversal on the ensemble mean. Uncertainty continues. Hopefully the above as he says is one random run wobble.

Kermit.de.frog

JMA eyeing what looks like could be a potential split in the first week of January. The stratospheric profile forecasts are something the JMA really excels on and I would recommend keeping an eye on it.

sryanbruen

I have had a chat with Mr. Simon Lee about what's going on. I am going to summarise what he has said along with some of my own thoughts to hopefully clear this up to a degree as there is bound to be some confusion.

Many SSW events are preceded by anomalous tropospheric wave activity. This basically means favourable weather patterns send planetary waves upward to disturb the stratospheric polar vortex. This doesn't need to be extreme to cause a huge disturbance as the state of the stratosphere going into the SSW event matters.

In early to mid-December, we had the Canadian warming which distorted the stratospheric polar vortex and led to a deceleration in U-60N. This makes the stratospheric polar vortex more susceptible to being perturbed by even an average amount of planetary wave activity from the troposphere. He reckons this might be contributing to some of the forecast uncertainty that we've been seeing with no clear cut signal as to whether we will see a major SSW (reversal) compared to the traditional record-breaking wave activity leading to an obliteration.

A reversal only matters truly if it's a massive event, there is not likely to be much significant difference in impacts if we're talking within one percentile either side of 0 m/s. All it means is it won't be classified as a major event if it doesn't reverse to easterly at 60N 10hPa. Not all events have to be "major" to give noteworthy impacts. Minor SSW events are not widely documented and thus we don't tend to hear much about them. Some events that come to mind are January 1991, December 2000 and January 2012 all of which were succeeded by blocking patterns leading to cold weather in Europe (not necessarily Ireland in all of them, cough cough February 2012).

Many people have said a major SSW event could shake up the pattern and even reduce the likelihood of cold weather here if we already have a -NAO to begin with. That is historically not true, at least according to Black & McDaniel (2004). I quote "The development of a -NAO during the onset phase of a SSWE is a very strong indication that a SSWE would likely anchor/intensify a -NAO in place for a prolonged period of time".

The possibility of -NAO/-AO we've been seeing in some of the medium range output is not stratospheric related.

We're seeing a weak vortex in the heart of winter which is very good if it's a blocking pattern you seek at this time of year. The last time we had a weak vortex at this time of year was 2020-21 which brought a very blocked January and subsequently the first half of February but we were "unlucky" if you like due to numerous factors such as the evolution of Storm Darcy in the case of February and the lack of a cold pool part in thanks to a record warm Siberia in 2020.

So the likelihood of a major SSW has probably decreased for the moment but a SSW is very much game on.

sryanbruen

As expected given this morning's EPS and the fact the EC46 is the extended version of this and runs at 0z, EC46 has backtracked on the major SSW with a reversal no longer showing on the ensemble mean.

A very significant deceleration is highly likely nonetheless which is a SSW, just not a major one.

Besides echoing everything I said earlier, the fact it's a minor event opens the floodgates to something more extreme down the line. As mentioned before, major SSW events act as a "cap" or cut off from tropospheric wave activity upwelling to perturb the strat and depending on the point in the season can re-intensify to strong levels aloft. This is not the case with a minor event.

So hypothetically, we could get a major SSW down the line on top of the minor event that is now expected starting later next week. Either that or it could do a last minute correction on models, which has happened before, to a major event. What this means for impacts, you never know.

Reminder that the medium range output is not related to what's happening in the stratosphere.

bazlers

For certain i am not very well schooled on this subject, but is this entering phase 3?

sryanbruen

https://www.boards.ie/discussion/comment/121543848#Comment_121543848

Yes that shows a highly amplified phase 3 by the end of the GFS run. Although it's not stratosphere related which this thread is about.

This is what an amplified phase 3 January looks like historically during an El Niño. Significant high latitude blocking with deep low pressure across Europe. This would probably be cold and wet. Very slight adjustment southward and it would be very snowy. This is without considering a weaker than average vortex and other things.

Given it's the end of the GFS run, not to be taken seriously. Could well be not as amplified just like the recent passage through phases 6-8 which flopped and time lag needs to be considered too.

sryanbruen

A big PV stretch is evident in the lower stratosphere but placement of lobes isn't great with some of the energy ending up over Greenland.

Very poor GEFS with a minor SSWE followed by a swift recovery by a significant minority - most keeping it around 20 m/s as far out as the forecast period goes.

We've lost the Ural blocking high which is a big loss as far as stratospheric disruption is concerned.

nacho libre

Without the Ural high there may not be further warmings to bring about an ssw later on. I am not confident the weakening of the zonal winds will be enough to bring about a cold spell.

I fear the promising model runs we see this morning won't last, with any high ridging to the north west collapsing. If that's the case, I hope it is on top of us so at least we can have some settled and frosty weather. The worst case scenario is residual energy left in Greenland churning out low pressure with our name on it while parts of Europe are in the freezer

Gonzo

We are back in familiar straw clutching territory it seems hoping that everything lines up at the perfect time. We are banking on a major SSW to save the final few weeks of winter and with each day that passes we are delaying the chances of cold and snow in the heart of winter and then we'll be looking at the end of February for a consolation prize before throwing in the towel.oh the joys of being a snow bunny I would like at least one major snow event before I retire in 2040.

nacho libre

https://www.boards.ie/discussion/comment/121546731#Comment_121546731

I remember years ago( back in the late 90) reading an article about climate change and how snow would become increasingly rare in Ireland by 2015 onwards. I dismissed it at the time but I am not sure now.

sryanbruen

We can regard the major SSW as a major flop I think albeit there was one single run with the EC46 mean getting to reversal..

A minor SSW isn't the end of the world but it's the swift recovery indicated by the GEFS, even accounting for their strong vortex bias, and the loss of the Ural high that concerns me.

nacho libre

https://www.boards.ie/discussion/comment/121546858#Comment_121546858

It's all going pear shaped, without the Ural high we probably won't get a major ssw. I would expect to see a change in the longer range ec 46 output now. We may as you say get lucky and eek out a cold spell due to the drop off in zonal winds, but I won't be shocked if any mid latitude block is fleeting. Over on netweather they were saying a major ssw was "nailed on".

Nothing is ever nailed on when it comes to cold. It's only ever nailed on when it comes to us getting rain.

sryanbruen

https://www.boards.ie/discussion/comment/121547421#Comment_121547421

Nailed on my ass. I even said in my post on 21st December: "I'm pretty torn to be honest. More runs needed." This indicating something just wasn't clicking with me to say a major SSW were to definitely happen. Was right to think this way. Netweather is full of hypers, least Boards is more grounded (although sometimes can veer towards the other extreme).

In some other news, the PV displacement will bring another risk of nacreous clouds. In fact, the whole of Ireland being engulfed by 10hPa temps <-80C according to the GFS on New Year's Day 2024 and 2nd January which is remarkable. So if you did not get to see them from the previous historic outbreak a week ago due to cloud cover, here's another chance. Remember they're best observed at sunrise or sunset (before and after) due to the low lying sun lighting them up like iridescence whilst they'll be much more washed out in the middle of the day when the sun is higher in the sky.

Billcarson

If we do end up getting a ssw this winter I really hope it's no later then early Feb. Knowing our luck it probably will be later. Not interested in the chance of snow in march etc.