My creativeness tends to thrive on days when the sun is hidden behind clouds. Rain is a bonus. I believe this correlation comes because without the sunshine, I have little outside attractions and I also have this sense of shelter, as the clouds are a cushion that surround and enclose me.
I am also a huge fan of thick fog, as long as I don't have to drive through it. I love how sheets of fog roll in and make familiar areas mystical. Once, when I was about six years old, I awakened to see our yard swamped in by thick fog. I've yet to encounter another day quite like this one. You couldn't see more than a foot ahead of you, and as a child I found this frightening and fun at the same time. It's strange when swirling mists flow around you and moisture drips from leaves and buildings. I believe this sensation is why such fog hung over Pittsburgh in Predators of Darkness: Aftermath. Add blood-thirsty monsters to the mix, and you have a page-turning scare ride.
Today it's raining, so time to get busy working on my novel.