The northern brickfielder is almost invariably followed by a strong "southerly buster," cloudy and cool from the ocean. The two winds are due to the same cause, viz. a cyclonic system over the Australian Bight. These systems frequently extend inland as a narrow V-shaped depression (the apex northward), bringing the winds from the north on their eastern sides and from the south on their western. Hence as the narrow system passes eastward the wind suddenly changes from north to south, and the thermometer has been known to fall 15 °F (−9 °C) in twenty minutes.[1]