squall line

A squall line is a meteorological term for a line of squalls, often 50 to 200 miles ahead of a cold front. It can also refer to the boundary between cold and warm winds in an extratropical cyclone, also known as a wind-shift line.1

These lines are often associated with thunderstorms and can produce violent weather, including tornadoes. A squall itself is defined as a sudden increase in wind speed of at least 18 miles per hour for one minute or longer. Squall lines can be hundreds of kilometers long and are often accompanied by rain, hail, or thunder. They are considered a type of mesoscale convective system, which are weather systems of intermediate size.234