Last Friday, a “cloud tsunami” startled the residents of New South Wales, Australia. Technically a “shelf cloud,” those on Bondi Beach saw what appeared to be a massive, several-kilometer-long wave stretching across the sky. The Australian Bureau of Meteorology issued warnings to the surrounding areas due to thunderstorms, heavy rains, and strong winds.
“[The shelf cloud] is created by a cold outflow from a thunderstorm lifting the moist air very abruptly, it is an outflow feature from a thunderstorm,” forecaster Christopher Webb explained to The Daily Telegraph. “When the rain from the thunderstorm comes vertically down it drags the air with it, it spreads horizontally and forms a gust front, you get the humid air being lifted abruptly from the outflow of the thunderstorm.”