Southerly buster

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 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 in the Tasman Sea, followed by the speedy advance of an anticyclone south of Western Australia and South Australia (around the Great Australian Bight). 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. The name 'southerly buster' initiated as a slang term used by Sydneysiders, though it has since evolved into an official weather attribute in the Bureau of Meteorology terminology.