Complex sentence: Cumulus mediocris clouds are similar, except that they have some vertical development, which implies that they can grow into cumulus congestus or even cumulonimbus clouds, which can produce heavy rain, lightning, severe winds, hail, and even tornadoes.
Split into simpler sentences: Cumulus mediocris clouds are similar, except that they have some vertical development. However, cumulus mediocris clouds can grow into cumulus congestus or even cumulonimbus clouds, which can produce heavy rain, lightning, severe winds, hail, and even tornadoes.