When is the beginning of a thunderstorm officially reported?

The beginning of a thunderstorm is officially reported when thunder is heard and local noise prevents hearing thunder because this criteria aligns with the established meteorological definition of a thunderstorm. Thunderstorms are characterized by the presence of thunder, which is produced by the rapid expansion of air due to lightning.

In situations where local noise might mask the sound of thunder, it is still recognized that a thunderstorm is occurring due to its other indicators, such as the presence of convective clouds, rain, or potential lightning. This approach captures the essence of a thunderstorm event, emphasizing the importance of thunder as a defining criterion.

The other options fail to capture the essence of a thunderstorm. Heavy rain alone does not guarantee that a thunderstorm has commenced, as rain can occur without thunder or lightning. Simultaneous observation of lightning and thunder does not constitute an official report of the thunderstorm until thunder is actually heard, regardless of concurrent sounds. Cloud formation without thunder does not meet the criteria for a thunderstorm, as the presence of thunder is essential in defining such weather phenomena.