Category Archives: Communication

Not all SSWs were created equal

Non-downward propagating SSWs? 

Major stratospheric sudden warming events (SSWs) attract widespread attention because they are now known to have significant impacts on the tropospheric circulation (e.g. Baldwin and Dunkerton 2001, hereafter BD01). Anomalies in the stratospheric circulation (often expressed as the Northern Annual Mode (NAM) index, or polar cap geopotential height anomalies) propagate downwards through the stratosphere into the troposphere, rather like “dripping paint” (such as BD01 Fig. 2). A major SSW is associated with the development of a negative NAM in the stratosphere; the “typical” response is the development of a negative NAM (or the associated NAO/AO) in the troposphere ~10-14 days after the central date of the SSW (when the 10 hPa 60N zonal-mean zonal wind becomes easterly) which can persist for several months.

However, not all SSWs were created equal – and some SSWs do not strongly couple to the tropospheric circulation. A recent study by Karphechko et al. (2017) classified major SSWs as “downward propagating” (dSSW) or otherwise (nSSW) based on the 1000 hPa NAM index following the event, and found 43% were nSSW – i.e., not followed by a strong and persistently negative surface NAM. This is not a small fraction of SSWs, and the atmospheric evolution following the two types was found to be significantly different. 

Our perception of SSWs in recent years has been highly influenced by a relatively unusual clustering of vortex-split, downward-propagating events (Jan 2009, Feb 2010, Jan 2013 and Feb 2018) which all had similar tropospheric impacts (all 4 of those events were followed by an outbreak of snow/cold in the UK, for example). The most recent nSSW occurred in Feb 2008. Thus, the announcement of a major SSW – particularly on social media – has become synonymous with a specific weather pattern.

In the nSSW cases considered by Karpechko et al., the composite (their Fig. 1c) actually shows intermittently positive NAM in the troposphere following the SSW – with the sign of the NAM opposing between the lower stratosphere and the troposphere for ~40 days following the central date. This is very different to the picture of dripping -NAM anomalies into the troposphere that BD01 made famous (which is consistent with Karpechko et al.’s dSSW).

Composites of all major SSWs are influenced by the higher frequency of dSSW and the stronger circulation anomalies induced, but this work suggests we need to be wary of these stratospheric events which don’t strongly influence what happens beneath. However, forecast models often struggle to predict the downward propagation – so forecasting these events is troublesome. It also presents a communication problem, which current forecasts (see below!) suggest we may be about to run into: a major SSW could mean a significant reversal of the normal tropospheric circulation (with the potential for “Beast from the East”-type events in the UK), or it could mean very little (e.g. January 2002 following the non-downward propagating Dec 2001 SSW). Predicting these differences, and understanding the mechanisms involved, is an area of active research – and something I hope to address in my PhD work.

Do current forecasts suggest nSSW or dSSW?

As I write this, we’re in a tentative stage – the main stratospheric heat flux event has occurred, and the 60N zonal-mean zonal wind has reversed to easterlies in the upper stratosphere. However, at 10 hPa we’re still decelerating – with the event expected to become ‘major’ around Jan 1 (Fig. 1 & 2) if current forecasts are correct (inter-model agreement has substantially increased now the upper-stratospheric reversal is in the observations).  The event looks very likely to be first driven by a wave-1 displacement of the vortex towards Eurasia, with an increasing likelihoodo of a vortex split (wave-2) to then occur, with the dominant daughetr vortex over Eurasia and a smaller vortex over N America (interestingly, this is opposite to what happened in Feb 2018). However, agreement on the split evolution remains lower than the displacement.

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Figure 1: Forecasts of the 10 hPa 60N zonal-mean zonal wind from 00Z December 27th. There is a good agreement between the GFS and its ensemble of a major SSW occurring around Jan 1st.

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Figure 2: ECMWF operational forecast from 12Z December 26th for 12Z January 1st showing a major SSW. Source: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/. 

So, predicting the tropospheric impacts is a challenge when the stratospheric forecasts don’t agree! The spread in the GEFS forecasts beyond 10 days is very large – with some members showing a quick return to stratospheric westerlies whilst others flirt with record-strong easterlies. There’s even some indication of bifurcation in the ensemble at longer ranges (perhaps relating to whether or not a split occurs), which may render the ensemble mean of less use.

Despite the uncertainty, one aspect that has been relatively persistent is the absence of a signal for downward propagation in the deterministic GFS (Fig. 3) and the longer-range models such as CFSv2 (Fig. 4). Comparing Fig. 3 here with the nSSW composite in the Karpechko paper is striking – there are many similarities, including the weak -NAM before the main event and the ~day 10 tropospheric +NAM development. On its own, this screams nSSW – but of course is just a single deterministic forecast from one model.

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Figure 3: GFS NAM analyses and forecasts from 00Z December 26th. Source: Zac Lawrence’s website (www.stratobserve.com). 

The CFSv2 initially trended strongly towards a -NAO for January 2019 as the SSW signal grew – but this has since decayed and transitioned more towards an Atlantic ridge pattern (Fig. 4). The model clearly picked up on a major SSW occurring – but, like all forecast systems this time, has struggled to predict the type of SSW. There is currently no indication (Fig. 5) from the CFSv2 forecasts of a widespread hemispheric cold outbreak (a “warm Arctic-cold continents” pattern).

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Figure 4: CFSv2 forecasts from Dec 1 – Dec 27 for January 2019 700 hPa geopotential height anomalies. Note the initial trend away from a +NAO towards a strong -NAO, before trending towards an “Atlantic ridge” pattern.

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Figure 5: CFSv2 2m tempertaure anomaly forecast for January 2019 from an ensemble of forecasts launched between Dec 16-25. Base period 1999-2010. Source: http://origin.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/. 

My advice would be not to hold your breath for a “Beast from the East 2019 Edition”. But as predictability typically increases once a major SSW has occurred, we should gain a much better picture in the first few days of 2019.

Takeaway message: the impacts of SSWs are more complex than whether it is a displacement or a split, and the mere reversal of the 10 hPa 60N zonal wind doesn’t mean you’ll be shovelling snow 2 weeks later.

References

Baldwin, M. P., and T. Dunkerton, 2001: Stratospheric Harbingers of Anomalous Weather Regimes. Science, 294, 581-584, https://doi.org/10.1126/science.1063315.

Karpechko, A. Y., P. Hitchcock, D. H. W. Peters, and A. Schneidereit, 2017: Predictability of downward propagation of major sudden stratospheric warmings. Quart. J. Roy. Meteor. Soc., 143, 1459-1470, https://doi.org/10.1002/qj.3017.

The Stratosphere – why do we care?

I study the stratosphere, the layer of atmosphere that extends above the troposphere from about 10-50 km. Friends and colleagues of mine often joke (I hope…) that “nobody cares about the stratosphere” *, primarily because it contains no real ‘weather’ – such as what happens in the troposphere. With little to no water vapour, it can’t be seen on visible satellite imagery – unlike the huge and beautiful weather systems in the troposphere. To visualise the stratosphere, we rely primarily on computer-generated graphics – and it’s not like you can walk outside and experience it, either. So, why do we care? What follows is a relatively simple (I hope!) explanation.

Weather forecasts, particularly on TV, often explain that our weather is “all down to the position of the jet stream” (the band of fast flowing air high in the troposphere that forms on the boundary between warmer and cooler airmasses). Now, that’s almost always true in the UK, but it’s particularly potent in winter – when the temperature contrasts either side of the jet become enhanced thanks to the Polar Night. One of the main driving factors behind the speed and position of the jet stream (particularly the Atlantic jet stream) in winter is… the stratosphere!

Rather like the jet streams we know and love/loathe in the troposphere that guide the development and evolution of weather systems, in the stratosphere there exists another jet stream – the Polar Night Jet (Figure 1). This encircles the Stratospheric Polar Vortex (SPV). Both of these form as the pole tilts away from the Sun in winter, leading to intense cooling. The strong temperature gradient then forms a jet stream and cyclonic vortex, which isolates the air within the vortex, and it cools further…etc. The Polar Vortex is a normal phenomenon which forms each winter – nothing sensational like some headlines suggest.

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Figure 1: GFS zonal wind analysis from February 4th 2018. Reds indicate westerly winds. A strong Polar Night Jet exists in the stratosphere, associated with a strong tropospheric jet.

Through a process known as stratosphere-troposphere coupling, the stratosphere and the troposphere beneath can ‘talk’ via the influence of planetary/Rossby waves. These very large waves in the mid-latitude westerly flow can propagate vertically from the troposphere into the stratosphere and influence the circulation there – a process known as wave-mean flow interaction. Sometimes, this is strong enough to strongly disrupt the SPV, and when that happens, the isolated reservoir of cold air is broken down and the temperature sky-rockets… by as much as 50C in only a few days. This is known as a Sudden Stratospheric Warming (SSW). Very strong SSWs – called major SSWs – occur in approximately 6 winters per decade, and result in a reversal of the Polar Night Jet to easterlies. The Polar Vortex is either displaced, split up, or destroyed (2018’s SSW is shown in Figure 2).

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Figure 2: The February 2018 Major SSW, as told through daily analyses from the GFS of 10 hPa wind (filled) and geopotential height (contours). This is classified as a ‘split’ SSW, for obvious reasons.

This has implications for our weather, because anomalies in the strength and position of the SPV and the Polar Night Jet can propagate downwards and influence the tropospheric jet stream. A stronger than normal SPV is associated with a strengthened tropospheric jet stream – and for us in the UK, that means Atlantic westerlies and generally mild winter weather. In contrast, following a major SSW, the easterlies propagate downwards (Figures 3 and 4) – resulting in a reduction in strength of the Atlantic westerlies. Sometimes, there can be a complete reversal of circulation – this happened in March 2018 with the infamous ‘Beast from the East’, bringing cold and snowy weather.

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Figure 3: As in Figure 1, but for February 17th, following the major SSW. Note the weaker tropospheric jet and surface easterlies as the ‘Beast from the East’ developed in response.

Thus, being able to predict the state of the Stratospheric Polar Vortex is a source of skill for wintertime forecasts. Moreover, because there tends to be some lag between the events in the stratosphere and their maximum impact at the surface (~2 weeks), stratospheric predictability can provide increased predictability on the sub-seasonal timeframe (~15-30 days). Additionally, anomalies associated with a major SSW tend to persist in the lower stratosphere for even longer – which again, is a source of skill.

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Figure 4: Anomalies in geopotential height for January-March 2018. Note how anomalies associated with the major SSW (red blob in the centre) propagate downwards like ‘dripping paint’.

And that is why we care about the stratosphere!

Further reading:

Kidston et al., 2015: Stratospheric influence on tropospheric jet streams, storm tracks and surface weather. Nature Geoscience, 8, 433-440.

*A tongue-in-cheek quote from Reading Meteorology’s weekly ‘Weather and Climate Discussion’ a few years ago that stuck with me was “the stratosphere – nothing of interest lies therein”. I plan to use that in my thesis…

“They get it wrong 90% of the time”

I was on a long train journey a few days ago, and ended up in conversation with the person next to me. When I explained what I’m doing (a PhD project looking to improve sub-seasonal forecasting), I was greeted with the all-too-familiar response of “oh, that’s good because they get it wrong 90% of the time”. Doing my utmost to supress just how much that sentence annoyed me with its factual inaccuracy, I responded with a comment about how there is still so much to learn about the atmosphere-ocean system, and ‘things can only get better’ (perhaps that song by D:Ream should be the soundtrack to NWP – or is it still too tainted by Tony Blair?). I also recently saw a post on Reddit’s ‘showerthoughts’ saying “Forecasting the weather is the only job where you can get it wrong every day and still have a job” – I refrained from responding to that!

Of course, “they” don’t get it wrong 90% of the time (you could easily argue the reverse is true) and a forecaster won’t still be in the job if they’re getting it wrong every day.

In the last few days we have seen a spectacular example of what NWP is capable of with the forecast of Hurricane Florence. We knew days in advance that the storm would reach category 4 status. The track into the Carolinas is now without doubt (though the exact motion when the storm makes landfall remains uncertain). So how is it that a forecast of a huge, turbulent, dynamic vortex can be so incrediby accurate to an extent that even amazes meteorologists – and yet the general public can have such a different opinion about their experiences of weather forecasts? How is it that this perception is so ubiquitous?

I had noticed over the summer that there were noticeable issues with app forecasts – and noticeable failures – but there is often good reason. Showers are difficult to predict to postcode-level accuracy, and, sometimes, “shit happens”. A great example of the latter occurred earlier in 2018 in Reading, in perhaps the only time I’ve really experienced the forecast go completely wrong. The forecast: a dry, cloudy day. However, the inversion mixed out, resulting in clear, sunny skies. That in turn lead to unexpected solar heating and thus unexpected instability, which generated a heavy (but very isolated) shower over Reading (perhaps its localised nature was a response to additional urban heating – yet another complexity!). A wonderful non-linear response – and something which as a meteorologist made sense. However, to a member of the public, it was unexpected rain that may have left them irritatingly soaked – and perhaps fostered a resentment of weather forecasters.

Forecast accuracy has come on in leaps and bounds over the last 30 years, but it seems public’s trust has not increased accordingly. I think part of this is how quickly one adjusts to a ‘new normal’ – I can draw a parallel to Internet connection speeds (remember when 1 Mbps was fast, yet now seems painfully slow?). I think a large part comes down to a lack of understanding as to why a forecast may go wrong. Rather like a medical diagnosis, it may make logical sense as to why a Doctor misdiagnosed, but the patient’s response may be filled with anger and confusion. And part of that comes down to the human body seeming naiively simple (because we all have one!) in the same way forecasting the weather may seem simple (just some fancy graphics and looking at clouds, right?). Both are hugely complex, but its usually only the experts who truly comprehend that.

Thus, it’s my conclusion that the more meteorology we can get out there, the better the public will trust the forecasts we make.

Edit: after writing this post, I received a wonderful tweet which showed that, for some, the incredible accuracy of weather forecasts is understood.
 

Why deny climate science?

Imagine you are an astronaut who has just returned from the International Space Station and you meet a Flat-Earther… how would you even go about that argument? 

Climate science and evolution are two sciences denied by many. In the case of evolution-denial, a creationist view is faith-based. Those who believe that God made the Universe 6,000 years ago (or equivalent) at least get a religious ‘kick’ out of it. I’m not saying that belief is a good thing (far from it – I think evolutionary science is an incredible human achievement and filled with beauty), but at least I can somewhat understand the mindset that leads to it (or the root of the belief – a religious text).

I cannot say the same for climate science denial. I just don’t understand what motivates it. What is the benefit to the individual? Does it make you feel good to think that all the experts are wrong?

Now, I do what I can to help the environment. I could do much more – I’m aware of the scale of the problem. But I don’t refuel a diesel car or use a petrol lawn-mower and feel riddled with guilt. My scientific opinion on climate change doesn’t follow me around like a dark cloud. I don’t overuse fuel in order to save money, primarily.

When the World Health Organization listed bacon (and other processed meats – of which you probably consume more than you think!) as definitely carcinogenic, I didn’t deny it – I’m not a medical scientist, and I’m sure good science was done in order to reach that conclusion. Equally, when we meteorologists and climate scientists announce that greenhouse gases are causing global warming, I don’t expect non-experts to take issue with that. Whether you act on it is something else, but don’t turn around and say, “Ha! Have you even considered the urban heat island?“. An every-day equivalent would be responding to an F1-trained mechanic informing you that your car needed a new engine by saying “Really? Did you check the oil?”. 

Of course they checked the oil.

In truth, what deniers say to climate scientists is often hurtful, and sometimes very difficult to respond to, purely because of the extent of the misunderstanding – not because we can’t support our science. It’s also plain baffling what some deniers say. When you’re just an excited or concerned scientist doing your thing, experiencing people thowing wild accusations at you is just…bizarre.

So, to all climate scientists – from those currently braving the harsh Antarctic winter, to those dealing with difficult questions from the media, to those who have been sitting coding for two days straight (or more!) – I salute all of you, for everything you deal with.

Going Viral: Some thoughts one week later

Sunday, July 22, 2018, 9:31 PM BST. I put out a relatively simple tweet comprising of two NASA GISS global temperature anomaly graphics – one for June 1976, and one for June 2018. After listening to the media and meteorologists alike comparing and contrasting the current UK heatwave with that of 1976 (something which I had earlier written about here), I felt it necessary to put it into some global context: the planet as a whole is far warmer than it was in 1976 – meaning that regardless of the final ranking of the 2018 heatwave in the UK, it occurred with a different climate background. The heatwave, alongside record-breaking heatwaves across the Northern Hemisphere, is symptomatic of climate change. It has a different meaning in today’s world.

I did not in any way expect the response the tweet gained – with close to 14,000 likes a week later. Initially, I thought it might rile up a few ‘climate change deniers’ (I had a genuine interest in what might get said in response…) but after it surpassed by previous highest like/retweet count within a few hours, I knew something special was happening! I have no real idea of how far and wide the comparison went, as some didn’t relay any credit back to me for the original idea (e.g. a BBC News special “Feeling the Heat” which aired on July 26, and Met Office blog post using their HadCRUT data). Not that it bothers me – they are NASA’s graphics, after all, and I’m just happy to get a conversation going. Special thanks to Leo Hickman of Carbon Brief for helping me keep track of the various media appearances!

I’ve been looking at NASA’s GISS maps for years – the plotting tool on their website is a fantastic way to play around with climate data. Seeing a comparison like 1976 vs 2018 wasn’t surprising to me, but it occurred to me that the public don’t regularly see imagery like that – especially in such a relevant and meaningful way. It told a story. Telling the general public that the globe is X degrees warmer than it was 100 years ago, or showing them a line graph doesn’t really work – hence the success of my tweet and other novel visualisation ideas, such as the ‘climate spiral’ and ‘warming stripes’ by Professor Ed Hawkins – the original climate science viral sensation from the University of Reading! As I stated in the tweet thread, graphics like those I posted shouldn’t be surprising – global warming isn’t new, and the planet has been much warmer (relative to normal) than it is currently (try plotting February 2016 for a real shock).

Perhaps initiated by my tweet, or perhaps a coincidentally, the media – and scientists – quickly began widely discussing the relationship between climate change and the heatwaves across the Northern Hemisphere. The tweet seems to be the reason why the phrase ‘global heatwave’ gained so much use – I have seen it used before my tweet, but my use of that as a hashtag seems to have made it mainstream. It is not meant to suggest everywhere is under heatwave conditions – just that this heatwave is part of something bigger; that the planet itself is warmer than normal (i.e., a ‘heatwave’). It’s perhaps a bit of flippant phrasing which I can understand disagreement with.

However, whilst this has been the best-reported and most clear-cut example of linking climate change to ongoing weather, it did strike me that in some cases it was reported as though this was, in some way, new. A BBC News article from August 2003 (“Heatwave part of global trend”) could have been extracted word-for-word and used in 2018. The story then: a heatwave in the UK, but also deadly heatwaves around the world as global temperatures rose. 15 years later, and the story is the same. Yes, we have come a long way in 15 years in terms of our understanding of the climate, but the story is the same and the expectations are (broadly) the same. How long until it is accepted that the future we predicted is now happening? How long until we stop speaking of ‘heatwaves are expected to become more common due to climate change’? Climate change isn’t something we should continuously speak of in the future tense – it has happened and it is happening.

If you’ve read this far and are still with me, I added some of my ‘in the moment’ thoughts on July 24 to my first post on Reading’s Meteorology PhD blog site, “The Social Metwork”.

Right. What do I tweet next?

Reading Half Cancellation: Do people believe forecasts?

This year’s Reading Half Marathon was cancelled at ~6:40 AM on the day of the race (Sunday March 18) due to substantial snow in Reading and the surrounding area (indeed, across most of England…). The cancellation of the event only ~4 hours before runners would be taking to the course was far from ideal, with many having travelled from afar and stayed the night in Reading. As expected, there was much consternation on Twitter and Facebook, with runners venting their frustration at the last-minute cancellation. As both a meteorologist and a runner, this clash of my two favourite things was a bizarre experience.

The question is – was this last-minute chaos avoidable?

The answer, in my opinion, is a firm YES. And I believe the problem lies with the trusting of forecasts.

On March 13 (5 day lead time!), it became very clear from forecast models that the “Beast from the East” would be returning in time for the race. Cold temperatures were certain, but the extent and intensity of snow was more difficult to predict. I tweeted the Reading Half, enquiring under what circumstances the race would be held off:

I received no reply. As I had seen the Bath Half cancelled with the first “Beast” event earlier in the year, I was very aware that the same fate could befall the Reading race.

By Friday March 16, the Met Office had issued yellow warnings for snow in Reading with a more severe amber warning nearby. The forecasts for Reading (models such as the GFS, ARPEGE, etc.) indicated 3-5 cm of lying snow on Sunday morning. With the model consistency, the severity of the alerts from the Met Office and the huge distances people travel for the Reading Half, I was convinced enough at this point that the race should be cancelled:

Still, the race organisers made no mention of snow and just kept mentioning cold weather. They were determined to ‘plough on’ (pun intended). The announcements were mainly that they were “gritting the route” – which is all fair enough, but hardly going to work very well with significant snowfall, and not going to help those travelling from afar.

Come Saturday, the Met Office forecasts had become worse for Reading, with heavy snow indicated all night. Forecast models still suggested 3-5 cm lying snow on Sunday morning across the south. Runners began to feel less at ease with the idea of it going ahead, and those travelling far wanted clarity.

By Saturday evening, with heavy snow already falling, the organisers cancelled the kids’ fun run, and left Half runners with the statement that a “final confirmation could not yet be made”. More bizarrely, they stated that “if conditions deteriorate further” then they would reconsider.

Prof. Mat Owens from the Reading Met department was just as confused as me, and expressed his feelings toward the race in a great tweet:

 

The forecast was for exactly that overnight deterioration to happen, and it was still the same message that had been said for days.

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Met Office forecast from 6 PM on Saturday indicating high likelihood of HEAVY SNOW.

I went to bed knowing the Half would be cancelled, yet having to “pretend” as though it were on…just in case it was…somehow. I woke up at 6:15 AM to the expected 3-6 cm of snow, and had to wait until 6:40 AM to find out it was indeed cancelled.

Now, before criticising too much, I want to say I love the Reading Half. I’ve run it twice, and both races being up there with the best experiences in my life. I’m aware it’s a tremendously big and important race.

However, why did it take until the snow was there, lying on the ground, covering the start line, the route and the finish line, with the M4 and M5 paralysed, for the organisers to believe the forecast? The situation that unfolded on Sunday morning was exactly as predicted. There must have been a moment on Sunday where the organisers said, “Oh…the forecasts were correct.”

The fact is, we can now forecast so accurately that a 1 day forecast is pretty much a certainty, unless it’s for a shower in a given location (which we might never be able to accurately predict). The reason we have made such advancements in forecasting power is precisely to avoid situations like this. It’s one of the greatest achievements of the human race. It’s also perhaps the most under-recognised.

What INFURIATES me, is that the announcement on the day claimed that conditions had deteriorated “more than forecasted”. That is, when it comes down to it, a lie. Either that, or whoever was providing the forecasts was not giving the best available forecast. They claimed to have been in contact with the Met Office…well, the Met Office forecasts I was looking at had expected exactly what happened.

 

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The official race cancellation announcement stating that conditions “deteriorated more than forecasted overnight”.

In my opinion, the announcement was to try and make forecasters a scapegoat for poor event management, with too much concern for a false-alarm scenario: “what if we cancel it and then it doesn’t snow?”. I was lucky to have not been so badly affected by this as I live only 2-3 miles from the start line – for those who travelled, I feel deep sympathy.

I sincerely hope Reading Half have learnt their meteorological lesson. And I hope people begin to understand that, whilst of course sometimes the forecast goes wrong, we can now trust it in times like these – and that’s thanks to the pioneering work of many meteorologists, data assimilation scientists and computer programmers over the last few decades.

It really is quite amazing.

But if anyone knows what reasons they had to fully believe the race could safely go ahead until 6:40 AM on Sunday, then please let me know – I’m all ears.

A Storm of Ex-Hurricane Communication

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MODIS imagery of Ophelia at landfall on Monday October 16, 2017.

It can’t have escaped the attention of many members of the general public that a storm by the name of Ophelia smashed into Ireland on Monday killing three. Met Eireann issued a RED warning 48 hours in advance of Ophelia’s arrival, which is unprecedented forewarning.

However, this post is not about the drool-worthy atmospheric dynamics that drove the storm nor its predictability, or its impact (or the bizarre yet stunning effect of advecting Iberian wildfire smoke and Saharan dust over the UK, resulting in orange skies).

I’m talking about communicating the threat.

Now, communicating weather isn’t easy. Meteorologists have to work out what they know first, then work out what the public need to know, what they understand, and then how this might be interpreted. This is then complicated nowadays by the world of social media, where meteorologists may tweet technical information which might get mis-represented by those less in the know.

Ophelia really brought storm communication to the forefront of my mind.

The term used by the NOAA National Hurricane Center to describe a storm of tropical origin that has undergone mid-latitude extratropical transition is ‘post-tropical’ (a term they picked up off the Canadian Hurricane Center, it should be said!). It’s a great phrase for meteorologists, I love it and advocated its use before NHC started using it operationally. Before I critique the communication any further, I should say I think NHC did a wonderful job with Ophelia, and I don’t think they could have done much better. I mean, they even had to change their graphics layouts because of Ophelia’s extreme north-eastern location!

My problem lies with the desire that BBC News, BBC Weather and to an extent, the Met Office, had with trying to emphasise that Ophelia wasn’t a hurricane, simply because it was no longer technically fitting that description. The phrases “ex-hurricane”, “tail-end”, “remnants” were used. The storm was “downgraded”. None of these phrases are suitable for communicating the severe threat, and some give the wrong impression entirely. Indeed, BBC News ran an article which said “The hurricane will be a storm when it arrives” which doesn’t really make any sense, other than perhaps suggesting it would be at Beaufort Force 10…storm force…which isn’t correct either.

There was even some egg-on-Twitter-faces when the Met Office tweeted that Ophelia was “now an ex-hurricane”. Simultaneously, NHC issued an advisory with the headline “OPHELIA STILL A HURRICANE”…which, given they’re the Atlantic’s official hurricane forecasting centre, means it was. The contradiction, in my eyes, is unacceptable and there were many tweets to the UKMO pointing this out.

Ophelia, with a likely sting jet, was capable of the same kind of damage as a landfalling tropical cyclone. It was in no way a ‘remnant’, and since it was still producing hurricane-force sustained winds, it was still Beaufort Force 12…i.e. a hurricane! I’m sure the people of Ireland will refer to it as ‘Hurricane Ophelia’. I don’t pretend to have the answers to this sort of situation, and certainly Ophelia was an unprecedented situation. But I think there should be consistency, and if a storm is severe enough, that shouldn’t be underplayed based on some sort of meteorological technicality. Do the public care about the difference between a symmetric warm-core cyclone versus an asymmetric warm-core cyclone when the impacts are similar?

Perhaps Post-Tropical Hurricane would work. Perhaps we should have some form of intensity scale for our named storms? Whatever happens, I think there can be improvement. These are the most severe weather events that these islands receive…why underplay them?