A southerly buster is the colloquial name of an abrupt southerly wind change in the southern regions of New South Wales and Victoria, Australia, which approaches from the southeast, mainly on a hot day, bringing in cool, usually severe weather and a dramatic temperature drop, thus ultimately replacing and relieving the prior hot conditions. Marking the boundary between hot and cool air masses, a southerly buster is sometimes represented by a roll-up cloud perpendicular to the coast, which appears from the south and coexists with the wind change, though sometimes there is little visual signal of the southerly's arrival. Southerly busters occur in the backside of a low pressure trough, followed by the speedy advance of an anticyclone from Western Australia. They are caused by the interaction of a shallow cold front with the blocking mountain range that aligns the coast, and frictional contrasts over the mainland and the ocean that disconnect the flow. Southerly busters occur about 32 times each year on the coast of southeastern Australia, with variable strength, usually in spring and summer. Although southerly busters are often associated with NSW and Victoria, they also occur on the east coast of Tasmania, New Zealand, and in Argentina and Chile. History 19th century In 1819, English explorer William Wentworth describes the southerly buster experienced in Sydney: ...They [hot northwesterly winds] seldom, however, continue for more than two days at a time, and are always superseded by a cold southerly gale, generally accompanied with rain. The thermometer then sinks sometimes as low as 60 °F (16 °C), and a variation of temperature of from 30 to 40 °F (17 to 22 °C) takes place in half an hour. These southerly gales usually last at this season from twelve to twenty-four hours, and then give way to the regular sea and land breezes... From the early days of settlement at Sydney Cove, sudden southerly squalls had been a problem for boats in the harbour. In 1829, a brickfielder as these squalls as were then called, laid the boat carrying Governor Ralph Darling and his family on its beam ends. Later Port Jackson boatmen would call it, the "Sútherly Búster". During the early days of the European settlement, Sydney's summer storms were accompanied by rolling red dust from the colony's brickworks. In 1869, following the connection of lighthouses and signal stations on the east coast of NSW to the electric telegraph