Squall Line

A squall line is a narrow, often continuous band of thunderstorms, usually forming ahead of or along a cold front or as a self-organizing mesoscale convective system. A cold pool of rain-cooled air spreads out at the surface, and its leading gust front lifts warm moist air to regenerate convection along the line, so the system propagates and can persist for hours over hundreds of kilometers. Hazards include sudden wind shifts, gusts over 50 knots, heavy rain, hail, lightning, and waterspouts at sea. The abrupt wind veer and pressure jump at passage make squall lines a recognized danger to small craft and ship handling.