Which of the following options typically leads to the formation of a cyclone?

The formation of a cyclone is typically associated with isobar convergence. This occurs when there is a decrease in the atmospheric pressure over a region, causing air to flow inward toward that low-pressure area. As air converges, it is forced to rise, which can lead to the development of clouds and precipitation. The ascending air cools as it rises, leading to further condensation and the potential for storm development, characteristic of cyclonic activity.

In contrast, stable air masses are associated with little vertical movement, which prevents the development of significant weather systems like cyclones. Temperature inversions create a layer of warm air above cooler air, which can suppress convection and prevent the upward motion of air needed to generate cyclones. Clear skies indicate a lack of significant weather patterns and deter the processes that lead to cyclonic formation. Thus, isobar convergence is fundamentally essential in driving the dynamics necessary for cyclone development, making it the correct answer.