Seen at sunrise after camping above Dulyn, in the lee of Foel Grach. Wind was coming from the 'right' of the photo.

How long before the rain came?

No rain all day! I think the lowish sun makes the clouds look darker than they are.

I don't think these are lenticular, as they tend to be very characteristic and usually presage rain. These look more like oscillations of warm and cold layers affected by air rising over the mountains. Or could be talking a lot of nonsense!