Southeast Australian foehn

Typically occurring from late autumn to spring, though not completely unheard of in the summer (particularly in eastern Tasmania),[a] the foehn effect mainly occurs when a westerly or south-westerly frontal system (which brings rainy and windy weather to southern capitals like Melbourne, Perth and Adelaide) passes over the Great Dividing Range and thereby provides clear to partly cloudy, relatively warmer conditions on the lee.

[b][5][6] The foehn effect on the coastal plains of southeastern Australia is mostly linked with the passage of a deep low pressure system or westerly cold fronts across the Great Australian Bight and southeastern Australia that cause strong winds to reorient virtually perpendicular to some parts of the Great Dividing Range, predominantly between late autumn into winter and spring, particularly during a negative AAO phase.

[15] During these conditions, an orographic cloud band, or the Föhn wall, builds up along the ridgelines of the southeastern highlands due to condensation of moisture as the air ascends the windward slopes.

In weather maps, a band of clear air called the Föhn gap, which is over the downwind of the Great Dividing region, can be seen between the wall and arched cloud cover.

Foehn winds may also impact other parts of Australia, such as east of the Great Dividing Range in southeast Queensland and northern New South Wales.

The effect is gradient; being more common and efficacious towards the South Coast (due to the latter region being in the track of prevailing westerlies, which exponentially falters north of 35° S).

[2] Areas that lie to the west of the Great Dividing Range are windward and therefore never experience a foehn effect under a westerly stream, with persistent cloud cover.

On the contrary, the Great Dividing Range also blocks frontal systems originating in the southern Tasman as well as the eastern Bass Strait.

[20][21][22] The Australian foehn has also impacted international sporting events and as well as recreational aviation, such as in 2007, when a light aircraft crashed in the Central Highlands due to severe winds on a region that is prone to mountain-wind waves.