Clean as normal , any problems then go back and re clean if asked
So if you cleaned the windows to a satisfactory standard then the next day there was a storm which left the windows dirty you would go back and re clean 
We offer a 24 hours guarantee that if this happens we will come back and clean the dirty windows. They need to call us. I won't go back and check any windows myself just in case.
It will be unusual for all the windows to be dirty so you might just have to clean one side of the house.
I think in 12 years wfp we have been called back twice. In the last case it was the lounge windows that are sea facing. When she phoned she complained that I hadn't cleaned them properly. It was a strange oily stuff on the windows which needed me to use a little soap to clean it off.
They are an old grumpy couple who sit in the lounge all day watching tv and looking out of the window. I walked back up the road checking the houses that we had cleaned and they were all the same. So it was something the rain brought in from the coast that evening. (Our cleaning area overlooks a bay which ships anchor in before an unloading berth becomes available at Teesport docks. I've never seen this residue before so can only think that it was some industrial population or something from the ship at anchor.)
I waited for further calls of complaint but didn't receive any.
We didn't get any moans when we cleaned the next time.
Unlike some, I detest cleaning in the rain so won't do it. On a couple of occasions I have continued to work through a downpour to finish a job off. Each time I have gone back later to check that job the windows have dried off perfectly.