Dust from the Sahara desert will cloud the skies of the US southeast this week in an annual weather event that doesn't always reach the American continent.

The dust clouds form as a result of an atmospheric phenomenon known as the Saharan Air Layer. As the name suggests, they've made a long journey across the Atlantic Ocean from their North African birthplace in the Sahara, the world's largest hot desert.

The Saharan Air Layer forms when massive quantities of desert dust are stirred up by tropical atmospheric waves along the desert's southern edge, ramping up around early June . Growing up to 4 kilometers (2.5 miles) thick, these dust plumes are blown across the Atlantic Ocean where they are further lifted by the denser, more humid ocean air.

The dust follows this westward course ev

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