Why some 'weather' pain before the rain

The other day I was speaking to my friend Cynthia, who asked when the storms were coming.
Now, this was last Wednesday, and our cold front wasn't expected to cross NC until Friday. Having spoken to other folks with joint problems who could forecast the weather days in advance, I knew what to ask. I learned from my friend that it was her hip talking to her and apparently quite loudly!
So, how is it that some folks can look out the window on a clear, sunny day while uttering 'rain's a-coming' ?
The most likely cause identified by arthritis sufferers and researchers is a drop in barometric pressure, which is the pressure exerted by the air around us. A drop in barometric pressure often precedes a storm, and the theory goes that a decrease in the air pressure can cause the tissues around the joints to swell, causing arthritic pain. Proponents of the idea use a balloon in a barometric chamber as a simulator. If the pressure outside drops, the air in the balloon expands. If the same happened in the area around an arthritic joint, the expansion or swelling could irritate the nerves, causing pain. Hopefully with high pressure moving in for the first part of our work week, Cynthia will see some relief!