Winter 2023/24 - A Post Mortem

[Blessed Weather]

On 14/02/2024 at 13:56, Blessed Weather said:

I wonder if the initial Canadian Warming was a fail tho? It might actually have played a role in giving us the favourable (for cold) NH synoptics in the form of a Greenland High that could well have delivered a notable cold spell. But agree that unfortunately the second SSW that occurred around the 17th January seems to have been the factor that on this occasion messed up the favourable synoptics. Win some, lose some.
Here's an extract from a NOAA blog dated 16th Jan discussing the Canadian event and imminent second event:

The polar vortex is acting up
.....But what makes the stratosphere’s current behavior unexpected and somewhat rare is that the polar vortex seems to be more disrupted at the lower levels, closer to the stratosphere-troposphere boundary. For more than a week, high pressure has been sitting in the troposphere over Greenland. It’s possible that the recent minor stratosphere warming reinforced this Greenland high pressure, which then drove a wedge into the stretched-out polar vortex in the lowest part of the stratosphere, splitting it into two lobes.

Full NOAA blog: https://www.climate.gov/news-features/blogs/polar-vortex/polar-vortex-acting

@Mike Poole @Met4Cast As raised in the Model thread, if you wouldn't mind I'd like to discuss with you whether the first Canadian minor SSW warming was of benefit or hindrance to getting cold into the UK back in January. I've started by copying my post of the other day in which Dr. Amy Butler co-wrote a NOAA blog on the 16th Jan. There's a clear pointer in there that the minor warming may have contributed to a Greenland High over the previous week (to the 16th) and would likely have primed the sPV for a further fall later in the month (which subsequently happened around the 17th).

Just look at the juicy charts that GFS and ECM were churning out at the time the minor warming was taking place on the 3rd Jan. These forecasts for the 13th Jan:

Next these series of tweets by Dr Simon Lee, highly respected atmospheric scientist, all made on the 4th January. He seemed quite clear that the minor warming was behind the forecasts for a negative NAM (AO). I won't copy the full tweet as I hate the way they make loading the Netweather pages jump all over the place. So instead the link is underneath:

The temperature of part of the Arctic stratosphere at 10hPa/30km has rapidly risen to +2°C... that's some 60°C above normal! As zonal winds at 60°N won't reverse, this is a "minor warming", but it is still an example of one of the atmosphere's most dramatic natural phenomena.
https://x.com/SimonLeeWx/status/1742830496998908272?s=20

The minor warming leads to a negative Northern Annular Mode (aka Arctic Oscillation), which -- combined with the absence of any preceding +NAM, especially in the lower-stratosphere -- looks likely to couple to the troposphere, typically fostering Greenland blocking-type regimes.

https://x.com/SimonLeeWx/status/1742830501696593963?s=20

Greenland Blocking-type regimes, favoured when the vortex is weak, drive colder conditions over northwest Europe, and to a slightly lesser extent over parts of the US & Canada. Exceptionally warm conditions also occur in the Labrador Sea & western Greenland, as in this forecast:

https://x.com/SimonLeeWx/status/1742830503940530413?s=20

Although the major SSW expected from a few ECMWF forecasts [https://x.com/SimonLeeWx/status/1739751236318920866?s=20] has not verified, this is a pretty decent minor warming (and better than nothing, if this is the sort of thing you enjoy!). It's taken the power out of the vortex right in the middle of winter.
https://x.com/SimonLeeWx/status/1742830508386476543?s=20

Furthermore: unlike major SSWs, minor warmings can be followed by further vortex disruption. Some forecasts hint that we could see another weakening of the vortex in mid-late Jan. For now, however, that's not worth fixating on: the vortex is weak, the NAM is negative. Enjoy it!
https://x.com/SimonLeeWx/status/1742830511343456619?s=20

I'll stop this post at that point and invite your thoughts. Needless to say the next discussion needs to be around what happened next, in particular surrounding the second strat event - i.e. the technical reversal / major SSW on the 17th Jan - and what went wrong to scupper expectations. But this tweet by Marco Petagna on the 23rd Jan suggests even the pros may have been taken by surprise? A strong reflection......?

Difficult to believe that only 5 to 7 days ago we were witnessing a 'technical' major #ssw sudden stratospheric warming..what a bounce back in the strength of the #spv stratospheric polar vortex!..soon set to perhaps be stronger than normal once more.

https://x.com/Petagna/status/1749903441567076604?s=20

 

[Met4Cast]

 Blessed Weather

Great post! I had actually been planning to create a post on this at some point in the coming days so good timing too. I think your conclusion on it being a strong reflection is probably correct, there were several things going on which likely led to the results we saw. It's quite difficult to "untangle" it all with limited vertical direction of travel on the charts, but I'll try & explain what I think happened using this strat observe chart.

1: Minor warming occurred in early January and as highlighted in your post, Amy Butler & Simon Lee both talking about this leading to the -NAM state & Greenland high, I think this is probably right but we also saw AAM anomalies propagating poleward with support from the MJO meandering in phase 3, this minor warming likely added some extra juice to what was already becoming a favourable tropospheric led pattern for Greenland blocking/HLB.

2: This -NAM then worked upwards into the stratosphere at a time we saw yet another SSW (whether this caused it or merely helped it? I'm not sure), I suspect this -NAM is the reason for the technical reversal we saw with this secondary strat event, the upwards propagation of -NAM however probably served to "cancel out" any downwelling from the major SSW in mid-Jan which then ultimately led to a breakdown in blocking and return to +ve zonal winds in the troposphere, as shown on the strat chart above due to the Canadian vortex shifting eastwards into the Atlantic sector. 

Quite a complicated entanglement of different forces/drivers coming together, one that would absolutely not have been possible to predict at longer ranges and something that seemingly caught even the experts out, let alone us mere mortals! From what I've read since, these reflection events are rather rare. 

So.. typical UK winter luck at play? 

[MJB]

 Penrith Snow February. A cold month (CET of 1.0C), with frequent northerly and easterly winds, and some heavy snow. 

[damianslaw]

I'm not clued up on this reflection event referenced, but seems sod's law it happened to prevent cold second half of winter. I'm.not sure its as simple as this, but it all shows just how unpredictable our weather is and the reason we keep speculating about what may happen, if it was all clear, this forum wouldn't be the place it is. Last summer caught many out, and this winter has as well it seems. Last summer pleased the chill rain summer  lovers, but the heat rain seekers had there pay back this winter instead. 

Edited February 16 by damianslaw

[Mike Poole]

8 hours ago, Blessed Weather said:

As raised in the Model thread, if you wouldn't mind I'd like to discuss with you whether the first Canadian minor SSW warming was of benefit or hindrance to getting cold into the UK back in January.

First, I think for clarity, we need to distinguish between the Canadian warming (which happened in early December) and the minor (as it was eventually) warming in early January.  The Canadian warming was responsible in my view for the strat vortex failing to form properly, these things used to be more common apparently, but we’ve not had one for 30 odd years.  These early winter Canadian warmings are, I understand, not strong enough to be technical SSWs.  This set in motion a weak strat vortex from the get go - there was a similar Canadian warming in November 1962, so there was understandable interest in what might happen, how this might progress.

That then brings us to the next event, which is the one you ask the question about - was the early January minor warming a benefit or a hindrance?  I think what was a hindrance was that it downgraded from the event that was initially modelled, which was a technical SSW and a favourable split as I recall, to a virtual non-event.  Had the split SSW event happened as initially modelled, there was a real sense that it might have locked in a genuine cold spell for the UK in the heart of winter.  But it didn’t, it was dropped by the models and the rest is history.  I’d be interested in the view of @Cheshire Freeze because he called the fail at the time as a significant moment in the evolution of this winter.

From then on, it seemed to me that the trop was leading the dance, as might be expected with a weak strat vortex, and the (just) technical SSW about 16th Jan looked in a sense to come up from the trop, rather than the usual top down warming event.  And it looks like we might get a further event which may be a technical SSW but only just.

None of this has ever been enough to assist in developing a UK cold spell, and the problem it seems to me throughout is that the strat vortex has rather been ‘neither nowt nor summat’ all winter!  By which I mean it has been so weak as to allow the trop vortex to run unfettered, but has never actually been able to actively drive the trop flow the other way (easterly) at our latitudes, i.e. we’ve never had any significant reverse zonal winds in the strat that might downwell to do that.  A weak strat vortex alone is apparently not enough to deliver a UK cold spell.

Well, that’s my take, anyway - but I’ve only been following this as a complete amateur for about a decade, which seems like a while but is only maybe 7 SSWs, we learn from each one, but they are all different, and learning is a slow process!

 

[Metwatch]

47 minutes ago, damianslaw said:

but the heat rain seekers had there pay back this winter instead. 

I can't say there are many on here who like the "heat and rain" combination in winter. Mild and sunny like February 2019/2008? Then yes I imagine those who like warmth and dryness any time of the year alike would enjoy that, which we didn't get at all this winter bar a few days, but very very few who like the mild and rain combined, so not much in the way of that payback!

Edited February 16 by Metwatch

[joggs]

I don't even wish it rip.

Absolute horror show with wet dominating.

We deserve a settled, warm spring for putting up with that excuse of a winter.

I swear the weather gods always have a right laugh at the British isles.....

[Cheshire Freeze]

 Mike Poole it was a sum of the parts thing for me really. A few things added up to provide the pessimism once we missed the boat on that split SSW.

@bluearmy has summarised things really well tbh in respect to any resultant blocking being too far N for the UK to benefit.

The Jan SSW was only a temporary displacement- against the backdrop of a strong Nino and a slightly displaced jet, there was never going to be a chance for N Atlantic blocking to get a foothold as the warming relaxed and the SPV headed back west. At that point there was good coupling between strat and trop, which meant the antagonistic response to N Atlantic troughing was enhancement of Euro heights.

The galling thing being, I believe that had a decent split of the SPV occurred, we’d have locked in to a blocked regime that benefited the UK in terms of cold, aided by the MJO. I honestly believe it would have been a noteworthy spell. The MJO on its own was not going to be enough.

TBH with you I’m still left scratching my head as to how that split SSW failed.

Edited February 16 by Cheshire Freeze

[Blessed Weather]

 Mike Poole  Cheshire Freeze  Thanks both - excellent summaries of events through December and into January. Imho Cheshire Freeze captures the essence of why the winter of 2023/24 will be remembered as one which promised much but failed to deliver:

"I believe that had a decent split of the SPV occurred, we’d have locked in to a blocked regime that benefited the UK in terms of cold, aided by the MJO. I honestly believe it would have been a noteworthy spell."

Sadly this sort of let-down allows some to question the value of teleconnections. But hey ho, onwards and upwards - the scientific community is steadily moving forward with research and analysis and every year we better understand how multiple teleconnections, all in various stages of waxing and waning, interact with each other.

Forgetting what happened down here on the ground, it's been a very interesting season for events up in the stratosphere, with Canadian Warming, minor SSW, major SSW and (in 2 days time) a second major SSW. Atmospheric scientist Dr Amy Butler rightfully excited by the prospect of 2 major SSW events in back-to-back months:

"Pretty psyched about the possibility of a double #SSW year! Last one was in 2010 though the situation was a bit different because one was in late March and barely qualified. Other double #SSW years were 98/99, 87/88, 70/71, and 65/66. Fingers crossed it pans out this year!"
https://x.com/DrAHButler/status/1755649856985567435?s=20

[TEITS]

My final word on this dreadful winter in which even frost & fog has been elusive. This has been probably one of the most disappointing I can ever remember. However even in Europe the winter has been incredibly mild. Many years ago I would always look at the temps in Poland if any E,ly was on it's way. Looking at the temps this winter in Miawa (Poland) apart from early Jan the max temps have been incredibly mild.

Im short of time so shall have to be brief.

Whilst I shall continue to look at the teleconnection predictions and seasonal models. I shall look and see what the teleconnections suggest for the whole of Europe rather than the UK. I do not believe you can use these forecasting methods just for a small island like the UK. The same applies to seasonal models.

Speaking of seasonal models. We know how SSW can affect the other teleconnections. We also know seasonal models cannot predict when a SSW in advance. So this makes you wonder why they even bother with these models or is the stratosphere less impactful than we think!

Whatever happens I shall continue to appreciate the efforts by members using teleconnections i.e Tamara, Met Cast etc even if you aren't convinced with the accuracy of these. I suggest others do the same because the likes of Tamara do this for free and wish to share their knowledge with the rest of us. If you were running a weather dependant business and paid huge amounts of money to these people I could understand your displeasure.

[Met4Cast]

4 hours ago, TEITS said:

Whilst I shall continue to look at the teleconnection predictions and seasonal models. I shall look and see what the teleconnections suggest for the whole of Europe rather than the UK. I do not believe you can use these forecasting methods just for a small island like the UK.

Thank you for the mention and I 100000% agree with this. 

Teleconnections cannot be used to forecast for the UK specifically but can be used for the broadscale direction of travel, i.e blocking regimes might be more likely or even develop but what that translates to UK specific weather is impossible to say! That includes the MJO & use of it’s composites etc. 

[phil nw.]

Just on one other aspect.

If ever a winter underlined the need to treat any models beyond days 4/5 with caution this was it.

I can't remember the number of occasions when broad scale medium term pattern forecasts have changed after promising looking cold set ups quickly disappeared as we got closer.

This was not just the operational runs as whole ensemble suites got watered down.

A season of big disappointments for cold lovers which I think has made many more of us more sceptical when cold chasing next year.

 

[damianslaw]

 Blessed Weather Noting winters 98-99 and 87-88 both mentioned as double SSW years, don't know the timings but neither was conducive to winter cold admittedly the following springs brought some cold in April.

The SSW factor is always an unknown, sometimes it brings the wintry good i.e. Feb 09, winter 09-10 and 12-13 and Feb 18, sometimes not so i.e. 18-19 and this year.

One factor not in favour this year has been the very warm El Nino perhaps underestimated.

 

[Snowyowl9]

A lovely cooldown for Spain back in 1987 to when this unprecedented cold spell happened..

 

 

[damianslaw]

Not that I understand fully the effects of volcanic eruptions other than large events tend to lead to global cooling thanks ti aerosols emitted into stratosphere, however the last big one in 2022 hunga tonga emitted water vapor instead which results in warming instead .. perhaps this has been a key factor. Typical the largest event since Krakatoa over 100 years ago results in warming.. seems everything destined to lead to warmth these days.. probably not as simple as one factor but notable how its affects has correlated with warming.. the lack of volcanic activity in medieval period also cited as a key factor for why it was much milder than rest of period since until recently... and without the greenhouse gas..

Edited February 19 by damianslaw

[Chasbrown]

Met office need to explain their constant theme of a stronger likelihood of winds from the East that they persisted with for weeks. Now quietly replaced with winds from the West. 

[Penguin16]

 Chasbrown Their outlooks have been dismal bordering on embarrassing. I really don’t know why they don’t scrap it. 

[Chesil View]

 Met4Cast

This is so true Met4Cast. And I think why some posters incorrectly poo poo the background signal or global drivers.

On a global scale the UK is tiny and to expect a Pacific based signal like the mjo to be able to forecast snow in Croydon is absolutely ridiculous.

As you say at best they give a broadbrush picture of the probabilities of what regimes may hold sway.

My personal feeling is that CC may probably making things like the mjo composites that we have relied on in the past somewhat less reliable.

Which if anything will make the great work by the likes of Tamara. Blessed weather and yourself among others even more difficult.

Rather like Catacol I am also becoming more convinced that without a proper SSW as opposed to technical SSW any extended or severe winter spells are unlikely to occur.

That is not say to we won't get snowfall even in south but I think what we do get will be shortlived without SSW.

I have not seen a decent depth of settled snowfall here in South Dorset since 31st Jan 2019. I'm sure I will see some more at some point but when? is the 64,000 dollar question.

 

[Rain All Night]

 Penguin16 They've actually done the opposite and expanded the reach of those forecasts by adding them to their mobile app recently

[lassie23]

Having performed a post-mortem on winter 2023-2024 I can concur that the cause of death was strangulation by the Atlantic, and the time of death was November 1st.

[Snowyowl9]

 lassie23

Don t expect nothing november 1st..

End of november we mostly do see anything besides the atlantic..

An easterly in this case..

[Chasbrown]

 Penguin16 I can't argue with that. Just curious as to the reasons behind the constant belief in easterly winds despite plenty of evidence to the opposite. And take into account they are generously funded by the taxpayer then they do have questions to answer.

[CryoraptorA303]

Starlings Roost Weather

STARLINGSROOST.DDNS.NET

According to the latest stats, February 2024 is now in position to overtake 1998 as the warmest on record. What a statement of intent for the year ahead. First December was extremely mild, then we got a new January all-time high, and now a new warmest February looks locked in.

Considering how much warmer February 2024 is than its relatives, if this is any indication of how severe the coming year is going to be vs those years, I would start preparing for something truly horrific to materialise this summer.

Edited February 19 by CryoraptorA303

[mountain shadow]

 CryoraptorA303 And this on the back of almost all long range forecasts and teleconnections predicting colder than average prospects for February. 

Very, very scary what is coming.

[rwtwm]

On 17/02/2024 at 16:38, phil nw. said:

This was not just the operational runs as whole ensemble suites got watered down.

Good point. We've seen apparently nailed on patterns switch at relatively short time scales, more than once. Most of the time disappointment follows a fuzzy ensemble resolving the wrong way. 

Does this mean that the ensembles are insufficiently perturbed? If guess that In an ideal world the ensembles will cover the broad probability space, with at least one of them getting it right.