Cyclonic weather system, animation. The distinctive anticlockwise spiral of a northern hemisphere cyclonic system is due to the Coriolis effect. In mid_latitudes, air flowing polewards north is deflected to the east by the rotation of the Earth. Conversely, cold air flowing south from the pole is deflected west. Where these two air masses meet, denser cold air lifts the warm air, forming a low pressure region, and the Coriolis effect imparts an anticlockwise motion around the central low. Such weather systems are common in temperate latitudes.