Cold weather is associated with several biological responses in your body:

There is a decrease of blood flow to non-essential tissues, and the decrease in oxygen perfusion of the tissues like joints and muscles can aggravate both acute and chronic pain.
Certain collagen rich tissues tend to shorten in colder temperatures and resist normal stretching. This is especially true of tendons.
The lubricating fluid of joints (synovial fluid) is more sticky under cold conditions and joints will not move as smoothly. This is especially true for joints that suffer from any degree of degeneration.
Cold exposure results in involuntary protective postural changes such as scrunching your shoulders into your ears, aggravating existing chronic postural problems of forward head posture.