Sore knees on cloudy days may be caused by osteoarthritis of the knee, autoimmune diseases and so on. 1. Osteoarthritis of the knee: i.e. knee osteoarthritis, the cause of which is still unclear and may be related to a variety of factors such as aging, obesity, trauma, etc. Knee osteoarthritis causes degenerative lesions inside the knee joint, osteophytes, etc., which leads to edema, pain in the knee joint, and in severe cases, deformity of the joint may occur. These symptoms may occur on cloudy days when the temperature drops. 2. Autoimmune diseases: Rheumatoid knee osteoarthritis will lead to an immune reaction of autoantigen and antibody in the joints, resulting in synovial hyperplasia and narrowing of the joint space in the knee joints, etc. Soreness and pain in the knees may occur on cloudy days due to a drop in temperature and a lowering of the immune system. When hyperuricemia leads to gout, there will be deposition of uric acid in the knee joint, which affects the normal movement of the joint, and the above symptoms may also occur. There may be other reasons for knee pain on cloudy days, so it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.