I've always felt that rainy days make for the best school days (rest assued, there have been many), simply because you're being productive on a day where you would be kept inside and bored anyway. I would much rather have a sunny day be a day to myself than a rainy one.
A lot of people are affected by weather. Cold tends to make arthritis worse, but rain can too. It's scientifically proven that the change of pressure when it rains is painful for arthritic joints. I'm one of those people who don't do well in the cold. I also don't do too well in the rain either, though its not nearly as bad. Regardless, I still think those are the perfect days to work: Sometimes I find its a distraction from the pain.
Then again, pain is really distracting in its own right. I've had days I couldn't focus at all, and usually by the end of the day I'm in a lot of pain anyway. In reality, there's no one day that's better for work or rest than another, it's how you're feeling that counts.