1. A strong wind characterized by a sudden onset, a duration of the order of minutes, and then a rather sudden decrease in speed. In U. S. Observational practice, a squall is reported only if a wind speed of 16 knots or higher is sustained for at least two minutes (thereby distinguishing it from a gust). See line squall, white squall, williwaw. 2. In nautical use, a severe local storm considered as a whole, that is, winds and cloud mass and (if any) precipitation, thunder and lightning. See squall line, arched squall, black squall, sumatra, Abrolhos squalls.