Could it be cows? There are lots of cows in the valley. Maybe they have found a way to turn their flatulence into cloud cover. Cows are vengeful creatures, and hate humans for eating them and for stealing their milk.
It's also possible that the cows are in the pay of PG&E, and the company is trying to increase energy use by making us run our air conditioners later into the night. Cows and energy company executives have an old alliance. It's not widely known that most energy company executives are not only vegans, but Vegans, from the star system Vega. This could get ugly.
Anyway, it's only going to be in the mid-80s on Saturday, and I'm looking forward to the brief respite from the heat. Plus I've got another casaba and there are feral cats to watch. I'm getting through the night, no matter what.