The rain water itself will not make the car very dirty. The splashes from the road are the main culprit. This is the reason why the upper part of the body panels are cleaner than the lower portion after the car is caught in the rain. In a light drizzle, the road grimes do not get washed away, unlike a heavy downpour. Hence, the splashes from the road contain relatively more dirt and debris. In the same school of thoughts, a heavy downpour clears up the road grimes. I’ve noticed in instances whereby my car looks as if it has undergone a car wash after it dried up from a heavy downpour. I believe a prolonged heavy rain also clears the air of dust particles, such that the water mark effect on the car is much reduced.
The rainy days also remind me that the holiday season is coming. As I drove pass Vivocity on Deepavali holiday, I saw that Christmas decorations are in the process of being put up. Drive safely and do not let the rainy season dampen your mood.