Just found this as noted that DarkSky API was dying soon, so ClearOutside I expect to also have issues?
From this much appreciated effort, seems all much of much ness across the sources, though presentation matters I guess. Anyway, seems the Window and the "Sky Windows" - Satellite feeds are the best way to extrapolate viewing conditions! Tend to use zoom.earth but sometimes a little hard to interpret night time cloud cover. Met Office %age cloud cover map also looks good.
As ever, micro climate (Gower Peninsular - sticking out into Bristol channel), has a big bearing!
Thanks for the analysys!