A haboob is a sandstorm that forms in the downdrafts of a thunderstorm. The downdrafts are caused by air being pushed down onto the ground, similiar to a leaf blower. They can be seen in deserts like the Saharan and in places like Arizona.
A thunderstorm can make strong downdrafts, which is just wind that blows down towards the surface of the Earth. When the wind hits the Earth, it starts to move sideways and picks up dirt and dust. It makes a cloud of dust that is bad for people, animals and plants.