Can't comment on the weather for the weekend but take a look at metcheck or the BBC - I went yesterday and it was very warm and sunny all day - glorious.
Course looks magnificent - did a course walk with Cordellia Croft and have to say that the enormous log on the way back to the lake which she said was nice and inviting nearly made me poop myself and I'm not even riding!!
Have a great weekend but I'd take a pacamac if I were you.....
