Before the rain:
– Dust off the vehicle to remove the collected dust and debris.
This will prevent the dirt from running around on your paint and might even help the rain give you a better car wash!
– A quick way to protect your paint pre-rain is to use a quick detailer which will leave a thin coat of slippery silicone and wax.
This will allow the water to run off your vehicle faster, dry quicker and prevent less particulates from sticking to the surface.
After the rain:
– If you have not prepared your car before the rain, it is really a good idea to get a complete car wash after the rain as soon as possible.
You must have noticed that after the rain cars get dirtier because the wet surface attracts more dust and air borne particles (if you follow the above mentioned procedure you will minimize these issues).
This way you will not allow the air borne debris to sit there long and damage the surface.
Air borne debris can be acidic in nature and it can etch the painted surface if it is left for too long.
– After removing the dirt, I recommend waxing your car which will add a layer of protection and help for the next storm (which hopefully won’t be for a while).
Source : Internet