There isn't a universally agreed-upon "second stage" in a thunderstorm. Thunderstorms are often described in terms of three stages:

1. Cumulus Stage: This is the initial stage where warm, moist air rises and forms towering cumulus clouds.

2. Mature Stage: This is the most intense stage of the thunderstorm. It's marked by heavy rain, lightning, strong winds, and possibly hail. This stage is when the storm is most likely to produce severe weather.

3. Dissipating Stage: This is the final stage when the storm weakens as the updrafts weaken and the downdrafts become dominant. The precipitation decreases, and the storm eventually dies out.

So, depending on how you're dividing the stages, the "second stage" could refer to either the Mature Stage or the Dissipating Stage. It's important to note that the stages can overlap, and a storm may not always progress through all three stages in a distinct manner.