June / July 2021 - A reversed NW / SE split, Flooding events in London, and some potent hailstorms

[Metwatch]

Summer 2021 was an atypical summer with the most unsettled conditions often in the south east but drier in the north. This was most notably the case in June. High pressure was often just north of Scotland but a trough would often be situated just south of England, bringing thunderstorms or more general rainfall.

 

The key aspect for this thread is the heatwave and severe thunderstorms / flooding in the second half of July.

Northern Ireland set an all time record high with 31.3C in Castlederg (County Tyrone) on the 21st July. Heathrow reached 32.2C which isn't that exceptional compared to some of the heat spikes in 2020 or 2022.

London had some flash flooding incidents on the 12th and 25th of July. 47.8mm of rain fell in a 24-hour period in Kew, most of it in just one hour on the 12th. The average monthly rainfall in July there is 44.5mm.

Flash floods: Parts of London receive a month of rain in one day

WWW.BBC.CO.UK

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Cars are submerged in water in some areas while train services have also been cancelled.

Thunderstorms cause flash flooding in London, submerging roads and some train stations | CNN

EDITION.CNN.COM

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Severe thunderstorms caused flash flooding across London on Sunday afternoon, sparking major transport delays.

July 2021 overall was quite thundery, with the 20th particularly thundery, and also the 24th, 25th and 28th.

 

20th July 2021 had a thunderstorm which brought hail up to 5cm wide In Leicestershire. An Environmental Agency rain gauge to the southeast of Kibworth, had recorded 72mm of rain over a 75min period, with 43mm of this falling in just 30min leading to flash flooding.

A nice video of the storms on that day around Bedford by @Zak M:

 

On the 25th there was the Brettenham storm in Norfolk where 180.5mm fell in 2 hours due to slow moving thunderstorms formed by a convergence zone. A very significant high end convective rainfall event for UK standards. Also unofficial rain gauge measurements suggested as much as 120mm may have fallen in the Woodford area of northeast London.

20 July 2021 leciestershire hailstorm reply.pdf hailstorm Leicestershire 20 July 2021.pdf Brettenham storm of 25 July 2021.pdf

[LetItSnow]

Ah, I remember this summer well! May 2021 had been very cold with cold, grey, wet and windy weather persisting late into the month. At month's end the weather warmed up and then early June had an abrupt shift to very warm and humid conditions. I remember this period well because it's when me and my current partner decided to become official after spending some time together and the weather was very fine and warm and we sat in a beer garden of a pub that would only a few weeks later be struck by lightning and burn down...

I remember one spoiler day, I think the 4th, which was very grey and wet, but then it reverted to a general spell of persistent but unexceptionally warm and sunny weather. The on the 17th the weather abruptly shifted with a very wet day or two lasting into the 18th. The second half of June 2021 was very grey and I remember it being quite wet at times. There was one day with some beautiful pink clouds in the evening. The 27th I remember being an absolute write off with persistent heavy rain and very low light levels. I texted my mother a picture of it and she was shocked as she lives in Cumbria and she replied with a picture of very summery blue skies!

July 2021 was mixed. The first week wasn't bad but it was unsettled, but I don't remember it being a washout. I moved to where I am now on the 30th of June so all my memories are of Islington/London in general since then. I remember the hot spell mid-month feeling very oppresive despite only being 32C, but it's possible the cool weather and cold spring weakened by defences a bit. Those storms on the 25th flooded the basement at my partners workplace.

August 2021, while not mentioned, I do remember well. Shockingly summerless month down here with very little sunshine and an almost complete lack of summer warmth. Almost every day was cloudy, though I don't remember it being overly wet, just a lot of cool and cloudy days. The Bank Holiday was very cold with maxima in the mid teens, drizzle and cloud. 

Overall summer 2021 I mostly remember for being a cool and very dull summer but with a fine period in early June and mid-July. Despite this, a very nostalgic time for me on a personal level coming to the city for the first time and at the start of a new relationship. Probably why despite being a cool and very dull summer my memories of it aren't being depressing. But then again, unlike some I don't hate cool and dull weather. I only use terms like "bad" to describe it for you all! 

Edited October 16 by LetItSnow

[Thundery wintry showers]

In Lincoln it was a mixed bag.

June was warm, dry and mostly sunny in the first half, with localised thunderstorms nearby on one day (I think it was the 7th). The second half was cooler and much cloudier, but not as wet as further south. The overall result was a warm and quite dry month with near average sunshine.

July was a very thundery month with thunder on 7 days in total. The first third of the month was statistically very dull but it didn't seem that bad to me, probably because there was a lot of convective activity and thunder about. The month's biggest thunderstorm hit late on the 3rd and went on for over two hours, and there were a couple of thunderstorms on a showery day on the 4th. The middle of the month had a spell of warm/hot and sunny weather. I remember getting a couple of thunderstorms on the aforementioned 20th, and there were a few more thunder days towards the end of the month. Overall, it was warm and wet with near average sunshine.

I remember August 2021 being a very "flat" feeling month where not a lot happened, there was no thunder, no convection of note and after a fairly sunny first week it was generally cloudy. Rather like in late August 2008, the real kick in the teeth came in the last week, when I had hoped for sunnier weather when high pressure sat almost on top of the British Isles, but ironically that spell ended up even cloudier than what had gone before, with the high placed such that Lincoln kept getting a continuous feed of stratocumulus off the North Sea. Overall everything was below the recent 1991-2020 long-term normal: cool for recent years (though still slightly warmer than the old 1961-1990 average), dry and exceptionally dull.

Overall for Lincoln the summer was quite warm and quite cloudy (entirely due to the dull August) with near average rainfall. Thundery activity was about average but concentrated almost entirely in a thundery July, with only 1 thunder-day in June and August combined.

[Harry233]

Ah summer 2021 I was one of the lucky ones during this season.

Coming off the back of May 2021 which had to be one of the worst ever months I’ve experienced being extremely wet, dull, cold and windy. It was most welcome. The weather flipped completely on the 27th May and turned very warm and sunny the only such spell of this month. Set us up nicely of what was to come. 
 

June 2021 was one of the driest Junes on record here. It was also quite sunny and warm but not especially so. The highest of the month was a pretty low 24.C but only one day failed to exceed 16.C here so temperatures were generally consistently fairly warm, the maxima at 19.5.C was 1.1.C above average so warm but nothing too unusual minima was close to average. Generally a very pleasant, quiet month with little to note. I do remember a freak downpour on the evening of the 4th but aside from that there was very little rain other than the odd shower from time to time. Pretty much every day had some sunshine. Coming after such a disappointing spring the weather felt amazing and with Covid restrictions slowly relaxing it was great to finally experience life again with some good weather.

July 2021 was very warm but only slightly drier and sunnier than average. Maxima temperatures again at 22.1.C were 2.C higher and only 2006, 2013 and 2018 have recorded higher here (2022 had an equal value to 2021) minima were also 1.C above average too. Like June the lowest maximum here was 17.C which was very high most Julys in this part have days that fail to exceed 15.C at least once a year. July started very warm and sunny but there was a bit of an unsettled spell between the 5th-11th. However it wasn’t anything too bad and there was still quite a lot of warm and sunny weather between some showers. From the 12th-26th it was absolutely brilliant being very warm, bone dry and sunny. Many days during this period reached 25.C but the highest maximum was only 27.C which is usually what the hottest day of the year is in my area. So again nothing exceptional. The 27th turned wet and dull but still reasonably warm and it was actually quite nice to get some wet weather after so much nice weather. Majority of the months rain fell during this spell. Had that wetter spell not had happened I think July 2021 could’ve been the driest July on record here. I only recorded 14mm of rain up until the 25th. 
 

August 2021 was another decent month but was probably the worst out of the three. The first half was quite unsettled but the second half was absolutely brilliant here. The month again had virtually no cool weather, the lowest maximum was still 16.C so again quite high for these parts. Pretty much all the rain fell in the first half but it was mainly in showers and there was still good spells of sunshine and dry weather between them so it didn’t feel too bad. It changed by the 16th to more settled and dry conditions and between the 23rd-30th was absolutely glorious here. With high pressure and a very light easterly breeze we probably had some of the best weather in the country during that spell. Mornings started misty and foggy but then it quickly burnt off and during the day it was virtually unbroken sunshine during that spell. I recorded a high of 26.C on the 24th which is slightly higher than average for August and I believe Perth was also the warmest place in the country that day. Absolutely Glorious spell of weather. The final two days did turn cooler and cloudier. August 2021 was again slightly warmer and sunnier than average with average rainfall. 
 

Overall an excellent summer here. Being pretty much settled the whole time bar a week in July and the first half of August but also always being consistently warm with no cool days. 2022 was a very similar summer here but did have a lot more cooler days and some very freak hot days. Summer 2021 was definitely a perfect summer here for people that like pleasantly warm and settled weather rather than extreme heat. It was probably among the worst in the south east though.