Sentence:  Approximately 1.25 miles of Virginia Highway 58 was rerouted to merge with US Highway 25E south of the gap. This photograph shows the phenomenon of the “<WSD>fogfall</WSD>,” when fog trapped in the meteorite crater of Middlesboro escapes [...] 
Meaning of the word marked with <WSD> tags:  A tumbling of fog from a higher area to a lower one, visually reminiscent of a waterfall.