The simile "shimmer in her voice mimicked the storm like a thunderous rain cloud filled with lead" could be improved for clarity and accuracy. The comparison between the shimmer in her voice and a thunderous rain cloud filled with lead is not immediately clear and could be confusing for readers.
Here's a suggested revision: "Her voice shimmered like the lightning in a thunderstorm, while the weight of her words rained down like lead." This revised simile compares the shimmer in her voice to the lightning in a thunderstorm, which is a more easily recognizable and concrete image. Additionally, the comparison of the weight of her words to lead falling from the sky is more coherent than the original comparison.
Overall, the revised simile creates a stronger image that is easier for readers to understand.