The rain will not ruin any work - that is an old wifes tail.............
I guarantee you that it is BETTER to clean in the rain rather than the sunshine
An excerpt from my book
"Let your windows do the talking""When is the best time to clean windows?
Surprisingly – in the rain! When it is raining there is no dust flying around – “wet dust cannot fly” and cannot therefore stick to glass.
Rainwater is very clean – much cleaner than tap water and will NOT affect the window cleaning process.
When it is sunny and windows are being cleaned the windows are left wet – dust particles can easily “stick” to the glass helped by the water and the dry environment around the building."