Potnoodles, it varied greatly. The summer/fall of 1940 in the BoB theatre was uncommonly good for weather, but there were also days of rain, overcast, and certainly heavy cumulus as to be expected in that part ofthe world. Fighters of both sides would fly high patrols frequently well above the cloud cover below, but would have to contend with whatever Mother Nature served up on ascent and descent. Bombers flew at the height assigned them, but the mission planners usually would take the meteorlogical reports into consideration. Clouds gave cover but also made it tougher to navigate with the inherent risk of icing thrown in.
The weather during the Battle of Britain was well-documented. There WERE cloudless days, just not full time.
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