Very interesting answers, sense of humor here is high level. Just can't stop laughing! (I was to place a picture because talking this is not as funny)
Listening to Art's song left me wanting to do the wash in rain review, I remember myself drying after a wash in the rain (light rain), I've gave up after some minutes, but I've tried! I can state it's impossible. Done. lololol
Then came Bob's song, remember when I sat and stared, what can you do more than listen to the rain (and watch the beading)...
Mission Failed!.
I believe a clean car performs better in the rain than a dirty car, I mean, for the dirty car the messy is bigger... Here in Brazil (my region) we have this variation every time, difficult not to rain every week, or weekend, or a day or two... it's a bright sunny day, it rains, then it's like nothing happened.
No way to trust climatic previsions. If you have a dirt car in this scenario, the rain will do a mess and the sun will come just after to dry that messy. 37-40ºC...
If clean, you only got some water spots... if dirty, you'll have to 'scrub harder' to get rid of it and maybe instill more swirls.
My opinion regarding the topic is explicit, wash before rain, during rain, and after!
Thank you for answers,
Kind Regards.