All rheumatic and other pain disorders seem to have this link between the weather and flare ups. Fibromyalgia, although not a rheumatic condition-but a central nervous system disorder, has been linked to changed weather as well. It was once difficult to find medical studies to support the idea of pain increasing when bad weather occurs. Notice the following reports that I have found:
John's Hopkins Report
http://www.johnshopkinshealthalerts.com/reports/arthritis/44-1.html
International Association for the Study of Pain
http://www.iasp-pain.org/AM/Template.cfm?Section=Home&Template=/CM/ContentDisplay.cfm&ContentID=2201
Weather and Fibromyalgia
http://dissertations.ub.rug.nl/FILES/faculties/medicine/1995/a.c.e.de.blecourt/c6.pdf
These studies revealed that barometric pressure, cold, and dampness were the contributing factors to increased pain in the participants.
Regardless, I asked other fibromyalgics about the link between weather and their fibro pain. I found that humidity, dampness and the cold really aggravated my symptoms and could lead to, if not directly cause, a flare-up.
Here are some quotes of validation from others living with fibromyalgia: (Note - names may have been changed or email aliases have been used.)
Whether it is humid, hot, cold, raining or snowing, the weather certainly affects us. That is something I know for sure.