A stationary front becomes shear line when the density contrast across the frontal boundary vanishes, usually as a result of temperature equalization, while the narrow zone of wind-shift persists for a time. This is most common over the open ocean as the temperature of the ocean surface is usually the same on the both sides of the frontal boundary and modifies the air masses either side of it correspond to it's own temperature. Stationary front's alway's stay the same.
