I am also fairly doubtful for Bradwell now, but I will wait until I see the weather forecast on Friday before making a decision. But this sort of high-pressure system is usually stable, so I'm not expecting today's forecast of very unpleasantly hot temperatures for Saturday to change. My version of Llani's Alderman's Ascent experience was the Pen y Fan race in 2018; I felt OK during the race, but then lay down in the finish field to quietly expire, until some kind person poured cold water over me.
Unfortunately my relatives never ask me to take them up mountains, so I will probably just stay at home and try to keep cool.