Biggin they are mammatus clouds from thunderstorms, they look particularly ominous during sunsets with different colours coming through they are nothing new lol
Tbf, they predicted the northern blocking episode in January, which did happen by the way, and they did a pretty good job in predicting these deep storms before they even existed. So perhaps they haven't been wrong all winter.
Even deserts struggle to reach 50 degrees, that's synoptically impossible on an island this far north. 40c was a push at the upper limit of what was possible in the most extreme setup.
Its not really a frost hollow it's half a mile from the coast and it was much colder than forecast last night, was predicted no lower than 5c but ended up 7c lower.