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Posted
  • Location: Exeter
  • Weather Preferences: Warm and sunny!
  • Location: Exeter
Posted

It'd be interesting to model how hot a summer with the same synoptics as 1976 in today's climate.  I'd expect the extreme temperatures to be reached earlier and to be higher than in 1976.  Perhaps there could be some unique unexpected differences too - perhaps with even higher temperatures we might see evaporation increase substantially, making it a more humid summer than 1976 too.  Perhaps it may have led to a true "heat dome" event like in the PNW in 2021.  What do we all think?  

  • Like 3
Posted
  • Location: south wales uk
  • Weather Preferences: hot and sunny
  • Location: south wales uk
Posted

Wish I'd have been older in 1976 to witness a great summer I was only 4,bet if it happened now it would definitely be roasting,I've spoken to mates who were all old enough to appreciate what a cracking summer 76 was, jealous definitely!!

Posted
  • Location: Islington, C. London.
  • Location: Islington, C. London.
Posted

 Earthshine A crude estimate you can do is look at summer synoptics of this era and imagine the thickness and uppers as slightly higher and theorise as to the potential max reached.

For example, there was a hot spell on the 8th/9th of June, 1976. Notice how tame it is with barely 15C uppers barely making it out of north Africa. Still reached 31C on the 9th which is quite impressive, but nowadays you would probably see the 15C upper covering the country with pockets of 16-18C across the south-east.

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Now for the main heatwave, it's a little tricker to ascertain because unlike most record temperatures we've had in the 21st century it was more the combination of very dry ground from drought that began in 1975 and a very strong anticyclone that had hot but not exceptional uppers, rather that an extreme heat pump out of NA. Now if the same pattern repeated in drought conditions with slightly higher uppers then you could definitely be talking about the 37-40C range.

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Here's a better example in my opinion, just 1 year earlier in August 1975, the first half of which is the hottest first half to August on record with persistent southerly/SE winds. This peaked at 34C on the 8th IIRC. You could easily imagine a repeat of this pattern but instead of the 20C line flirting with the south-east coast, the 25C line instead. A persistent spell like that in the first half would be an absolute inferno.

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A repeat of that today/in 10-20 years time would probably translate to a hotter first half than August 2020 which had similar uppers to August 1975, the warming giving an absolute high of 36C instead of 34C.

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And before anyone thinks such a spell would be impossible, it already happened in June 2019! But surface winds meant we escaped the damage. Something of that extremity happening in early August would perhaps be even hotter for the uppers.

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  • Like 7
  • Insightful 2
Posted
  • Location: Exeter
  • Weather Preferences: Warm and sunny!
  • Location: Exeter
Posted

 LetItSnow nice post, thanks!  Really interesting analysis.  I wonder if we will see another repeat this century.  Back then it may have had an enormous return time, but perhaps that has shrunk in the current climate.

Posted
  • Location: Cheshire
  • Weather Preferences: BWh
  • Location: Cheshire
Posted

I do wonder how long it'll be before we see a repeat. You'd think some time before 2030 but who knows. If you believe the conclusions of the Oltmanns study, the right conditions will exist for it to occur within the next four years.

Posted
  • Location: Skirlaugh, East Yorkshire
  • Location: Skirlaugh, East Yorkshire
Posted

1976 was basically just a "perfect storm" so to speak. What's interesting is we've had a background warming since then of about 1.3-1.4C, so if it were to happen again you could probably be looking at the following CETs:

June: 18.3C
July: 20.0C
August: 19.0C

Summer CET: 19.12C

We've had a 19.8C July in 2006 and a 19.2C August in 1995, so both are very possible. June at 18.3C is a question mark as everything over 17.0C (in 2023) were recorded over 150 years ago.

I think the chance of a repeat of such a perfect storm summer is remote, but individual months very likely. Its similar in winter, where a perfect storm like 1963 is an extremely low chance, but the odd cold month like December 2010 could always pop up. Getting prolonged weather of any type in the UK is never going to be easy.

  • Like 4
Posted
  • Location: Ireland - East Coast
  • Location: Ireland - East Coast
Posted

It's an intriguing question. One thought I have is with the underlying warming since the mid 70's, we are nearly half a century away, is 1975/76 even possible, I mean by that, would micro tipping points develop given the dry heat interacting with warmer seas etc and the process kills itself off, not just micro but at macro scale. 

In any case temps are climbing so I suppose it's safe to say it would be even hotter, but some doubt in my mind about stability.

  • Like 2
Posted
  • Location: Swindon
  • Location: Swindon
Posted

 LetItSnow I've been thinking for years that the dry conditions that assisted the 1976, and 2022 heatwaves are likely to be more severe in the future. There's something we don't yet talk about in the UK, because it hasn't happened yet - multi year soil moisture deficits. 

It doesn't sound very interesting until we start to understand the impact of this. With a warmer climate we are undoubtedly losing moisture faster during the growing season. This isn't so bad if we have more rain, but due to natural variability, we aren't always going to get the increased rainfall every year, but we are likely to endure more warmth virtually every year compared to a few decades ago. If we had this situation, with soils not saturated by the end of winter, we could go into a new growing season in a bit of trouble. Already on the back foot, we'd run the risk of another failed soil recharge season the following winter. 

So take this scenario, where we start the second spring with soils well below saturation point, and bring in synoptics like 1976, and we'll endure a record breaking summer. With plants and trees seriously struggling, rivers dried up and no moisture on the ground, there would be no mitigation whatsoever. 

  • Like 1
Posted
  • Location: Cheshire
  • Location: Cheshire
Posted
On 02/09/2024 at 10:37, Earthshine said:

I'd expect the extreme temperatures to be reached earlier and to be higher than in 1976.

I'd agree on the second of these points but not necessarily the first. In 1976, the top temperatures in Surrey where I lived were 94.1 to 95.6F on 26th - 28th June and 3rd July (Currie).Of course, those temperatures have been exceeded in the last 50 years, but later in July and in August. I am old enough to remember 1976 well and the thing I remember most is that the heat was very dry, with scarcely any rainfall and certainly no thunderstorms until the end of August. I think it would be different now, more humid and prone to breaking down more readily into thundery downpours, such as happened here in Cheshire in June 2023.

Posted
  • Location: Hampshire
  • Weather Preferences: Warm-by-day sunny thundery summers , short cold snowy winters.
  • Location: Hampshire
Posted (edited)

 Downburst It is interesting that really sustained anticyclonic periods in summer are proving to be rather difficult. Even the July and August 2022 anticyclones lasted around 10 days each before breaking down to something a bit more changeable.

1976 seemed an entirely different ballgame entirely, as did (more recently) August 1995. The most recent examples of sustained anticyclonicity lasting two weeks or more seem to come from summers 2013 and 2018 but they are exceptions.

Edited by Summer8906
  • Like 1
Posted
  • Location: Liphook
  • Location: Liphook
Posted

 reef December 2010 was basically an equivalent to a Jan 63/Feb 47 when looked at in terms on anomalies. Those sorts of months will synoptically happen from time to time unless warming shifts the broader synoptic so much they can't go as cold anymore, which is imo doubtful.

In terms of summer months, I think both 2018 and 2022 (and even June/Sept 2023 to a lesser extent) have given a good indicator of what is possible, and just in terms of temperature as long as background warming continues it will need a lower and lower return rate to challenge 76.

 

Posted
  • Location: Maidstone, Kent
  • Weather Preferences: Anything below 0c or above 20c. Also love a good thunderstorm!
  • Location: Maidstone, Kent
Posted

Some good insight here, it would be a belter for sure! 

I'd like it to happen soon to silence those who say 'Summers aren't as hot as those in the '70s so climate change is a myth'. It would also make decision makers sit up and address water and food security as well!

  • 4 months later...
Posted
  • Location: Pendle, East Lancashire, North West England
  • Weather Preferences: Winter: Dry and sunny Summer: Sunny and 18-23°C
  • Location: Pendle, East Lancashire, North West England
Posted
On 03/09/2024 at 11:23, reef said:

Getting prolonged weather of any type in the UK is never going to be easy.

Hmm… 🤔 Not so sure about that.. Certainly easy to get months of dull and wet weather!

Posted
  • Location: Skirlaugh, East Yorkshire
  • Location: Skirlaugh, East Yorkshire
Posted

 East Lancs Rain Not easy, but not impossible of course.

It's also worth noting that although it has been overly dull and wet over the last two years, the weather has not always been the same. We've been particularly unfortunate in the last 12 months that when high pressure has arrived, it was in the darker part of the year and always a "dirty" high. The pattern wasn't always the same.

  • Like 1
Posted
  • Location: Somewhere in SE England
  • Location: Somewhere in SE England
Posted (edited)

 reef Not to mention, the previous 18 month run is surely one of those rare instances of unusually persistent conditions. Just not the kind that many people would want.

As to answer the question, as the 1976 airmass was very windstill, I'm not sure the absolute maxima reached would be all that much higher, but still noticeably so. It's important to keep in mind that 1976 didn't challenge the all-time high of the day. The commonly quoted figure of 35.9°C is a probable nonsense at a highly questionable station (the next highest temperature that day was 34.8°C at Wisley, so over a degree lower and the best part of 80 miles away) and the highest reliable figure from the 1976 heatwave is 35.5°C on June 27th at Southampton. Very hot for the era, and certainly within the ranks of what the hottest heatwaves could be expected to produce back then, but not quite the 36.7°C recorded during August 1911, assuming the record is correct which I believe it to be.

To return to the point, today I believe we'd see an absolute maximum in the realms of 38°C. I don't think endogenous heating could produce 40+°C in the UK, and you'd need some sort of southerly wind to do it. August 2003 had very high uppers, higher than 1976 and was also very windstill, and in the end we got 38.5°C from that, and this was after months of dryness, a very warm June and a heatwave in July in the target area, so I believe this is near the maximum for what can be done endogenously for now. Perhaps accounting for warming since 2003, 39°C could now be possible from endogenous heating.

What would potentially be more alarming is how long the very high temperatures would last. Today we'd probably be looking at more 8-12 days above 34°C than the modest five or so that were achieved in 1976. This would be extremely dangerous and would also likely lead to daily minima reaching 23°C or maybe even 24°C towards the end.

As @LetItSnow pointed out, August 1975 would be perhaps even worse than a 1976 today, as the uppers seen along with the persistent southerly that was observed would mean a prolonged period potentially above 35°C, and possibly exceeding 40°C on the hottest days. This would be especially bad if there had already been a heatwave and/or a notable dry spell beforehand.

Perhaps even worse of a scenario would be for a notable drought like the one in 1975/76, a heatwave like August 1975 or 1976 occurring, and then a Coningsby heatwave occurring later in the summer. With the ground that dry, and absolutely roasting hot from the heat that has already occurred, surely absolutely astronomical temperatures would be seen if a Coningsby-like heatwave were to spawn in. An August 2003 spawning in would probably be even worse than that, what with the aforementioned conditions, plus another 22 years of warming. Perhaps 40-41°C would actually be seen from such a heatwave in this scenario.

@richie3846 Brings up an excellent point. Warmer ambient conditions means a higher rate of evaporation, so that moisture is now progressively lost faster. To see this in action we only have to look at the drought of 1975/76 vs the drought of 2022. 2022 simply had a prolonged period of drier than average conditions without serious rainfall for eight months, and by August it was rivalling or outright surpassing 1976 in terms of river levels in the south west. 2022 beat what took 1975/76 over a year of bone dry conditions in just eight months. What's the difference? 2021 into 2022 has a complete lack of a winter, and a stunning lack of freezing or even cold conditions in spring. The end result of this was moisture was simply lost far faster than it was in 1975 and 1976.

Higher rainfall in the autumn/winter will also not offset this, as progressively more of said rainfall will evaporate and leave the surface before it can become groundwater into the future. Warmer, sunnier springs and hotter, potentially drier summers will also cause us to have a progressively harsher evaporation season where we lose more and more water in the warm season on average anually. Milder, sunnier winters with heavier rain will mean less rain settles as groundwater.

As climate change progresses, the UK will become more and more vulnerable to droughts, heatwaves, and also floods, as dry desiccated ground is very bad at absorbing water and sudden heavy rains cause intense flash floods like those of August 2022 during droughts.

As for those saying that increased rainfall etc. will mean a feedback where the heatwave is more likely to break down, sorry but that's not how weather works. Evaporating moisture can't kill an anticyclone and spawn a thunderstorm or something. The only way it can influence what goes on above our heads is by cooling the airmass down slightly, which causes the anticyclone to lose potential, which can mean it potentially breaks down earlier. However soil moisture has to be high for this to have any real effect, so after a prolonged dry spell it doesn't really have any impact. After a 1975/76 level drought in the modern period, there isn't going to be any moisture left to evaporate out of the ground. Rivers will have run completely dry and the soil will be totally desiccated.

2022 didn't feature an extremely prolonged heatwave like 2018, 2006 etc. because it was a boom-and-bust hot summer, where we got intermittent phases of extreme heat and then mid-high 20s. The overall result is a hot summer on average but it's quite different from a prolonged heatwave, which has less variation but also lower extremes. 2003, 1990, 1989 and 1911 were all summers like this.

Spells like spring 2020, summer 2018 etc. clearly show that persistent anticyclones are well and truly possible over the UK and aren't declining in any way. 1976 was a freak. The last event even remotely comparable to 1975/1976 was August 1947. Before that there was only really summer 1911.

If anything, since the 1989/1990 duo, very hot summers like these are well and truly on the up. In fact the 1975/76 duo is somewhat of a turning point, as it was only seven years later that the summer of 1983 occurred. Before 75/76 these really hot spells were a few a century kind of deal. After the duo the frequency of very hot spells have increased significantly. After 75/76 you have 1983, 1989, 1990, 1995, August 1997, 2003, July 2006, July 2013, 2018, 2019 (somewhat), August 2020 and 2022. Before 75/76 you have June 1957, August 1947, June 1940 maybe, the brief August 1932 heatwave, 1911 and September 1906. Before 75/76 there were six separate very notable heatwaves, and five of them were individual months or events. Post 75/76 there have been 11.5 of them (.5 for 2019), and only four of those were individual months or events, the rest spanning multiple months or the whole summer.

Edited by Sceptilli0naire
  • Like 4
  • Thanks 1

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