Which statement is true regarding squall lines?

Squall lines are often nonfrontal features that can develop ahead of active cold fronts, associated with larger-scale weather systems. The statement that they "are nonfrontal and often contain severe, steady-state thunderstorms" highlights two key aspects of squall lines. First, unlike typical thunderstorms that can be linked directly to frontal boundaries, squall lines can form in the absence of such fronts, driven instead by atmospheric conditions like moisture convergence and instability.

Additionally, when these squall lines do form, they can produce severe weather, including heavy rainfall, hail, and damaging winds. The term "steady-state" indicates that these storms can maintain their structure and severity over a period of time, unlike other transient thunderstorm types. This characteristic is important for weather forecasting and understanding potential hazards, as squall lines can pose significant threats to aviation and surface operations.

This understanding of squall lines is crucial for meteorologists and pilots alike, as recognizing the existence and behavior of these systems can lead to better preparedness for associated severe weather events.