Foggy days in the UK, is that not associated with high pressure and low temp?
I would have thought that would lead to a decrease in density altitude as the effect of moisture is negligible.
When we are calculating take off performance on the shiney jet we do not input any information about the humidity, obviously Boeing do not consider the effect on performance to be worth worrying about.
Edited, I had been going to write an INCREASE IN DENSITY and then became distracted, thanks to thud105 below for pointing out my error.
Last edited by Council Van; 27th Jan 2017 at 13:34.