A WALL of dust and debris advanced through Arizona last week, inundating the city of Phoenix. During the dust storm, which hit the city on 5July, there was near-zero visibility and winds of up to 110 kilometres per hour, according to the Phoenix office of the US National Weather Service. Radar data suggests that the dust storm travelled 240 kilometres in total, with the dust reaching 1800 metres in altitude. The storm's leading edge stretched for almost 160 kilometres. Meteorologists classify this kind of storm as a haboob. These are formed when thunderstorms release their precipitation, causing the strong winds that were being sucked into the storm to blow downwards and outwards instead. If the thunderstorm "collapses" over a desert, the strength of these winds stir up the dust and sand.
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