What weather phenomenon indicates the start of the mature stage of a thunderstorm?

The start of the mature stage of a thunderstorm is indicated by the onset of precipitation beginning to fall. During the development of a thunderstorm, there are three main stages: the cumulus stage, the mature stage, and the dissipating stage.

In the cumulus stage, the storm is primarily characterized by the build-up of cumulus clouds, which are developing due to strong updrafts of warm, moist air. As these updrafts continue and sufficient moisture accumulates, the storm reaches the mature stage. This is precisely when precipitation starts to fall from the cloud, which is a clear signal of the storm reaching its peak intensity. At this point, both updrafts and downdrafts are present, leading to heavy rain, strong winds, and sometimes severe weather conditions.

The other weather phenomena listed, such as sudden wind changes, rapid temperature drops, and the occurrence of lightning and thunder, typically occur during or following the onset of precipitation but do not individually mark the transition into the mature stage. Thus, the commencement of precipitation is the definitive marker of this important phase in a thunderstorm's lifecycle.