Advancing Dust Wall

Advancing Dust Wall is an original illustration set in Nile-Sahel Transition, Sudan. It lies in the tropics, where the climate is hot semi-arid steppe.

A dense vertical wall of dust advances across the horizon with a rolling scalloped leading edge. Directly above it hangs a dark blue-grey shelf cloud. The foreground air is still clear and dry, and thorn shrubs stand on parched ground waiting for it.

Why does the dust wall arrive ahead of the storm cloud?

A haboob is the visible edge of cold air collapsing out of a thunderstorm and spreading along the ground, lifting dust as it goes — which is why the dust wall and the storm cloud arrive together, dust first. It requires a hot dry surface with loose material and a storm capable of producing a strong downdraft. That combination belongs to the seasonal margin between desert and savanna.

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