Hi Tomo,
I'm always a bit leary of rain and very windy weather
The wind will carry particles of muck carried into the air from vehicles, blown off roofs and whipped into the air from trees and so on.
Heavy rain + heavy wind = spotty windows (Trad or WFP)
And it will happen time and again too.
Now and again we get the dirty rain, fortunately that doesn't happen very often (not inland at least)
And just heavy rain is rarely a problem, neither is windy weather on a dry and bright day.
Dust may get blown around, it may settle on the glass and in droplets of water if you are a WFP'er, but often it will dry out fine.
The dust particle remains a dust particle (but not always
)
All we can do is go out there and do our job...and be prepared to call back and rectify when you know da
mn well that you are working in conditions when the windows are going to be dirty again almost as soon as you have finished
Ian