They form or have broken off from a larger cloud, and are generally sheared by strong winds, giving them a jagged, shredded appearance.

Cumulus fractus in particular form on the leading and trailing edges of summer storms in warm and humid conditions.

Fractonimbus are a form of stratus fractus, developing under precipitation clouds due to turbulent air movement.

In rainstorms, scud often form in the updraft area where the air has been cooled by precipitation from the downdraft, thus condensation occurs below the ambient cloud deck.

Scud are very common on the leading edge of a thunderstorm where warm, moist air is lifted by the gust front.