What is defined as a squall line?

A squall line is defined as a band of intense thunderstorms, typically associated with a cold front. It is characterized by a narrow zone of severe weather that produces heavy rainfall, strong winds, and sometimes hail or tornadoes. The thunderstorms in a squall line can be quite severe and often extend for many miles, leading to hazardous conditions.

Squall lines are often formed when a cold front advances into a warm, moist air mass, triggering the rapid uplift of air and the development of thunderstorms along the frontal boundary. The organization of these thunderstorms into a line is what differentiates them from scattered thunderstorms, which can occur individually or in clusters without the same level of organization.

Other options refer to phenomena that do not accurately capture the nature of a squall line. A series of moderate rain showers describes less intense precipitation without the severe characteristics of a squall line. A cold front with stable air suggests an absence of convection and severe weather, which contradicts the conditions typically present in a squall line. Areas of scattered thunderstorms do not represent the organized structure of a squall line, which is essential to understanding the severity and intensity associated with it.