What kind of clouds indicate possible precipitation

Cumulus clouds I think ask Google

Nimbostratus clouds and Cumulonimbus clouds.

Nimbostratus clouds are low-level, rain clouds that form a uniform layer. These layers cover the sky, producing overcast conditions, and uniformly extend in all directions. They have dark color and produce steady and prolonged precipitation.

Cumulonimbus clouds are large, puffy clouds with strong vertical development. They are formed by the upward movement of warm, moist air. In their mature stage, they also produce strong downdrafts of cold air.

Tip: clouds producing significant precipitation usually include the prefix or suffix nimbo, so when you see that suffix/prefix, be sure that this type of clouds indicates possible precipitation.