Which feature is associated with the dissipation of thunderstorms?

Widespread downdrafts are indeed a key feature associated with the dissipation of thunderstorms. During a thunderstorm's life cycle, it typically has an initial phase characterized by strong updrafts that build the storm and create heavy precipitation. However, as the storm matures, the processes involved lead to the formation of downdrafts, which occur when the cooler, denser air from aloft sinks and spreads out at the surface.

These downdrafts are crucial for dissipating the storm because they help to reduce the upward motion of air that fuels the thunderstorm. As the downdrafts dominate, the storm's ability to maintain its structure weakens, ultimately leading to the storm's decay. This interaction between updrafts and downdrafts is vital for the life cycle of thunderstorms.

In contrast, strengthening updrafts are associated with the development and intensification of storms, not their dissipation. The formation of new storms and the formation of cirrus clouds can occur during a thunderstorm's development or in its aftermath but do not directly contribute to the dissipation process. Therefore, the presence of widespread downdrafts is the primary factor leading to the weakening and eventual dissipation of thunderstorms.