[M.D. Holloway]

Vash - It has to do with pollution. During the week, as pollution increases due to traffic, exhaust from trucks and cars has particultes in it as well as other things. But the particulate matter is what allows water drops to form. They actually form around it the way perals are formed. When they hit a certain density, they fall from the sky. It just so happens that it takes about 4 days in a pretty urban area for this to occur - just in time for the weekend. Kinda like seeding a cloud.