Skunk, the general location is around the area known as the Machynlleth loop.
I've never had a heads up warning from any one, so it is turn up and hope. On Tuesday it was well into late morning before we saw anything. We'd been there (on the hill), since 08:30. I've had one day when only one a/c came past, I've known others who have had 'virgin' days. I find locations through large amounts of detailed map reading. Once you get there though what looks good on a map may not be practical or safe!
If you give it a go follow the countryside code, and make sure you have proper bad weather clothing, as the area has it's own micro climates high off the valley floor which can change in minutes. The last thing you want is a yellow taxi ride or worse.
