Weathercocking happens when the center of lateral resistance to the water is in front of the center of lateral resistance to the wind. The stern is being blown around like a weathervane, pointing the bow into the wind. Adding weight aft will move the center of lateral resistance to the water aft, a good thing. So will lowering a skeg. The bad thing is that if you move weight aft by moving the paddler you also move the center of lateral resistance to the wind aft.