Why does the weather affect our mood?

Research: Says it really doesn't. There are simply some people who love summer or love rain or love winter.

Darkness: Lack of exposure to light has been associated with depression. Also increased pain has been associated with slowly falling barometric pressure seems to be the major association. You will notice that in a storm system coming in fast you are fine. That front that takes days to come in. There is also fair weather pain from a high pressure area moving away from you. The mechanism of both is unknown.

Vitamin D3: With less sunlight, we make less Vitamin D3 which is important to our mood.