To cast this spell, the priest had to touch the beneficiary. When cast upon a living being, this spell lasted for up to a year or until it was activated by speaking a secret word, whichever came first. To be effective, stormcloak had to be activated while the recipient was threatened by a storm in a sufficiently large body of water; perhaps about to be dashed upon some rocks, struck by lightning, battered by flying debris, or capsized and drowned. The recipient could be in a vessel, or above or below the water, as long as the secret word could be spoken. Once triggered, stormcloak guaranteed that the protected person would not die as a result of the storm. Events were ordered by whatever means necessary to ensure the safety of the individual regardless of how improbable and coincidental the sequence of events may have seemed.
Priests of Umberlee were not allowed to cast this spell on themselves or each other.
This spell was very popular among seafaring folk and gave some Umberlant priests a steady source of income.