tilted troughs have a northwest to southeast orientation. In the Southern Hemisphere, the positive tilt will be southeast to northwest and the negative one southwest to northeast.

A trough will usually begin with a positive tilt as cold air moves toward the Equator. The trough will become neutral (North-South) and then negatively tilted as the energy carried by the cold air races east through the atmospheric circulation and distorts its shape. The positive tilt is thus the building phase of the trough and the negative tilt is the dissipation