A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. ... Strong straight-line winds can occur where the squall line is in the shape of a bow echo.

What happens in a squall line?

A squall line is a system of thunderstorms that have formed into a line. This often occurs ahead of a cold front, where wind shear combined with unusually widespread lifting of the lower atmosphere causes convection to become arranged in a banded structure.

Where does a squall line occur?

a. Squall lines. Squall lines are frequently observed over convectively active midlatitude regions such the central United States during spring and summer and they occur over parts of the tropics as well. Tropical squall lines usually propagate westward, whereas midlatitude squall lines propagate eastward.