In California, we had a way to predict the weather. If you washed your car, it was a sure thing that it would rain the next day!
Not really, but it felt that way at times.
I remember sitting in traffic on highway 4 and thinking that my car had the most dirt on it. Now, my car is the cleanest I've seen lately out here in the country! If I leave it out for a day or drive by someone using their tractor, my car is the dirtiest until the next rainfall, which could be tomorrow!