I climbed Scoat Fell on a beautiful day when the cloud mass was gathering in the north. You can make out the cloudy haze above High Stile. The top photograph is as normal and the bottom was taken through a polarising filter. There was a distinct pale level above the cloud. The sky does get paler blue as you get nearer to the horizon as Mie Scattering becomes important but I think this was more pronounced. My hypothesis is that above the cloud there was an increased level of water vapour which led to a more pronounced Mie Scattering effect. This is the scattering of all colours of light by water molecules - all colours so looking white.
