Going out for a Picnic on Saturday?

Interestingly, in highly-populated areas, especially in the ones located close to the sea/ocean coast, there is a 22% higher chance of rain on Saturdays than on Mondays. The reason is pretty simple: heavy traffic and industrial pollution during the 5-day working week result in production of extra clouds and thus increase the likelihood of rain on Saturday.

I discovered this fact accidentally trying to find the information about the nature of "rain from clear skies" effect. I had never seen such an effect before, but observed it twice for the last few weeks here in Yorkshire. Unfortunately, I have found no relevant information about this amazing phenomenon on the Internet (similar effects are quite usual for the lowlands located near the mountains, but there are no high mountains around). The only idea that comes to my mind is that such rain could be caused by extremely high humidity level in the atmosphere, so atmospheric moisture condensates directly to water drops. Or maybe it's due to massive air flows and whirlwinds that take water from a sea and move it over the land. Will investigate it deeper when I have some time.