Personally I'm allergic to rain.
I will work with the odd drop around but nothing more.
Firstly. its not very easy to wash windows in the rain when you have to wear glasses.
Secondly, I once did a first clean and as I started the heavens opened up and I got soaked. My wet clothes made the seat of my van wet which took days to dry out and wasn't very pleasant.
BTW the customer was none the wiser to it raining as she thought it was because I had wet the windows.
She was most surprised when she opened the front door to pay me. I went back the next day and checked the windows; they were perfect.
I cleaned that customer's windows for the next 7 years until she passed away a few years ago.