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1. (aviation) '''C'''eiling and '''V'''isibility are '''OK'''; specifically, (1) there are no clouds below 5000 feet above aerodrome level (AAL) or minimum sector altitude (whichever is higher) and no cumulonimbus or towering cumulus; (2) visibility is at least 10 kilometres (6 statute miles); and (3) no current or forecast significant weather such as precipitation, thunderstorms, shallow fog or low drifting snow.