Storm Thrall

 is a Master-level Conjuration spell in that permanently summons a Storm Atronach. The atronach will follow and defend its master until banished, killed, or turned.

Perks

 * The Elemental Potency perk will raise the Atronach's health from 500 to 750.

Attributes

 * Weight: 1
 * Value: 1350

Acquisition

 * Phinis Gestor at The College of Winterhold sells this spell after the Dragonborn completes the Conjuration Ritual Spell.

Bugs

 * In some cases, it does not show up in "Active Effects", while Flame Thrall and Frost Thrall do. Additionally, the Storm Thrall is called a Storm Atronach instead of Storm thrall.
 * When used with the Twin Spells perk, it will not work with Storm Thralls.
 * After buying the spell storm thrall from Phinis Gestor, it might not cast saying you don't have enought magika even if you do.