“Why do my knees hurt when it rains?”

Rain or just wet weather is usually associated with a falling barometric pressure which results in a negative or vacuum like pressure in already irritated tissue allowing swelling. This distention is painful to joints already irritated with arthritis even minor amount from wear and tear or underlying disease. Likewise sunny days and blue skies are associated with a rising surrounding barometric pressure which like a sleeve support puts gentle pressure on the body tissues and makes your aches and pains less.