When I arrived at the airfield, vis. was such that I could just about see the far end of the runway, say about 1.6k, so instead of flying the aircraft, I washed her.
By the time I'd finished, the vis had improved enough to commit aviation, but from 2,000 ft it was still only about 5k, clear enough to see, but not that good. So after 30 mins. I decided that the aircraft had been blown-dry and came home.