A squall line is a line of severe thunerstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts. Severe weather along squall lines can be expected if it displays a line echo wave pattern (LEWP) or if the line is in the shape of a bow echo.