The west coast trough affects temperatures, winds and thunderstorm development near the west coast of Australia during the warmer months of the year.
What are they?
The west coast trough is a semi-permanent feature of the surface pressure pattern near the west coast of Australia during the warmer months, and is the dominant influence on west coast weather conditions at this time. The trough is a zone of low pressure that develops at the boundary between warm continental easterly winds driven by the sub-tropical ridge to the south, and cooler maritime air from the Indian Ocean.The trough typically extends northwards to meet a heat low (a low pressure system formed by hot rising air) in the northwest Australian Pilbara region and can move westward off the coast, or inland depending upon the variation of the prevailing synoptic flow. A typical sequence is for the trough to deepen near the west coast over a period of days as winds to the east of the trough tend warmer northeasterly under the influence of a strong high pressure system in the sub-tropical ridge, in or south of the Great Australian Bight. With the approach of a cold front to the southwest of Australia, the trough will generally move eastward over inland Australia. The sequence of trough development begins again when a high following the front moves south of Australia and easterly winds again become established near the west coast.A similar heat trough system is also present over eastern Australia and is known as the easterly trough. West coast trough patterns are observed in other parts of the world, for example near the west coast of southern Africa.
