Protoss who follow the Khala can produce such a storm by closing their mind to the outside world, sending out psychic "ripples" that are disruptive to other lifeforms, tearing apart their brains. Such storms can also damage vehicles and the landscape itself. Such is the power of a psionic storm that it can send shockwaves through the air around it.
The storm is a physical display of the psionic power of a high templar. It concentrates all the psionic energy over a given area, so overlapping storms have no greater effect than a single one.
While Dark Templar can create psionic storms, only through the discipline of the Khala can it be controlled.Khalai who have not mastered the use of the ability can try to control psionic storms unleashed by Dark Templar (and similarly-powered protoss, such as the Tal'darim) but it frequently results in the death of both participants as they burn out like a star. Individual protoss who have used both types of abilities (such as Adun) have faced a similar fate.
Several hybrid breeds were shown to have the ability to channel psionic storms.
During the Discord, Dark Templar lost control of their powers, creating storms across Aiur which killed many protoss and destroyed parts of the landscape itself. Storms appeared on other protoss colonies, such as Khyrador.
During the End War, the loss of the Khala deeply impacted the high templar. Nonetheless, in their races darkest hour they continued to hone their skills, allowing their psionic storms to last longer and recharge the shields of their allies.
Artanis possesses high templar with the ability to use psionoc storm. When reaches Artanis level 6 in Co-op Missions, he unlocks several upgrades for psionic storm in the templar archives. At level 7, Artanis's archons gain the ability to use psionic storm.