In reply to JTM:
> I was thinking more of Scotland, but jeez, that's worrying. And the Durham Dales... Langdale sounds better on the other hand.
Where are you going and when?
I think in the west of Scotland they are often bad for a time in May or June then can be ok until another hit in the autumn.
They like damp days with no wind, so sunny with a bit of wind is fine (often worse in the evenings).
Edit I don't think the winter/spring weather makes a difference to them.
Post edited at 21:07