<P> The Atlantic cold fronts that move into and across the subcontinent, especially during the cooler months of the year, are frequently associated, the day before, by a coastal low that moves ahead of the front . Under these circumstances the southerly or south - westerly onshore wind of the coastal low gradually diminishes in intensity over the course of 12--20 hours, when it is replaced by a westerly wind (which may temporarily reach buster proportions) and a further drop in temperature accompanied by rain, indicative of the passage of the cold front . Thus, particularly in Cape Town, an obvious berg wind is generally regarded as a harbinger of cold, wet weather . </P> <P> Coastal lows are orographically trapped weather systems that also occur in other parts of the world, where there are mountain ranges between 1000--4000 km in length . Thus they occur along the coast of Chile, eastern Australia and the west coast of North America, as well as on the eastern side of the Appalachian mountains of the United States . In each of these cases the weather systems are trapped vertically by stable stratifications, and laterally by Coriolis effects against the mountains . However, only the South African and the South American coastal disturbances are "coastal lows"; the remainder are generally produced by coastal ridging . </P>

Why berg winds are regarded as a threat to farming communities along the east coast of south africa