Many people swear that the colder and damper months exacerbate any underlying wear and tear in the joints and it has certainly been damp in the last 5/6 weeks.
It may perhaps be something to do with the necessary lower atmospheric pressure (allowing more tissue swelling), the cold causing stiff tissues and poor circulation or our mood, and therefore pain tolerance, to dip.
The knees are not blessed with a protective layer of fat, nor any muscles to generate warmth, so they do suffer in the winter.
It may be a little late to consider a circulatory herb like Ginkgo as its effects can take a few weeks to build but you may wish to consider trying some ginger and a warming balm, such as Tiger Balm (the white one is less ferocious than the red).
If your symptoms do persist into spring, please consider some Atrosan® Devils Claw.