Well, weather at Cadwell is a bit of a law unto itself anyway! I'm fairly local, but it can be blue sky here, and rain at Cadwell. It's in the Lincolnshire Wolds (what passes for hill around here!) and it's often damp.
I've ridden Cadwell 7 out of the 8 track days I've done this year and half of them started off wet. Often, then track will dry out by mid morning so don't be put off.
I love the place though, and don't need much of an excuse to ride there.