Looking at the June ‘league table’, it’s incredible that two years recorded Junes of 18C (1676!) and 18.2C (1846) and that they were in a time when our weather was cooler in general.
In fact the top 3 Junes for warmth are all pre 1900 whereas the top 3 July and Augusts are all post 1975 😲
Looking further down the table, very warm Junes are mostly a feature of the 19th and 18th centuries with only 7 Junes since 1900 featuring in the top 20 warmest.
I had a look to see what data was available other than the CET mean daily data for June 1846 and noticed that our friend Gav did one of his vids for that month in 2021, so thanks to him for thishttps://www.youtube.com/watch?v=Zy_StYzfuW0
This is just the synoptic charts for each day as it is about as far back as you can go for detailed info but you can see why is was such a scorcher. Other than the last week when the Atlantic broke through (much like 2023) the rest of the month had high pressure over ot just to the east of the UK and not so far north as this year bringing in more of a SE-S rather than NE-SE flow. There was a short period where an "Azores Ridge" type westerly came in but not for long
Bearing in mind that the Global temperature is about 1.5-2C warmer in the UK than in 1846, this 18.2 would be about 20C in "todays money" and even so the final week of 1846 was distinctly average