Is it really the case that weather affects arthritis?

Weather and joints: Cold or wet weather or changes in barometric pressure can worsen stiffness or pain. Joints have pressure receptors in them that can become more sensitive if a joint is damaged or has arthritis. That's why grandma could forecast better than the weatherman.

Weather related pain: 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 is completely unknown.