Cut-off lows are low-pressure systems that develop south of South Africa. They get cut off from the prevailing westerly winds and move north, bringing much-needed rain and sometimes snow to the Western Cape and KwaZulu-Natal. About 11 cut-off lows pass over South Africa a year, but only one is likely to bring strong winds and heavy rains that cause flooding. Since the 1980s, more than 20 have resulted in fatalities, making them the leading cause of weather-related deaths in South Africa. The problems are exacerbated by urban development and poorly maintained infrastructure.