A highstorm is a fierce weather system on the planet of Roshar. They occur once every few days, or at command of the Stormfather, and move from stormward to leeward from the Origin. East of Roshar, the highstorms are incredibly destructive. They progress across the continent, though they weaken gradually as they cross, and are mostly broken by the mountains east of Shinovar.
A highstorm has three general stages. The leading edge, or stormwall, is the most dangerous part of the storm. Immensely powerful winds generate a wall of dust, water, and larger debris. It is shown that it is powerful enough to carry large trees long distances into the Shattered Plains. The main body of the highstorm carries less debris, although the winds are still strong enough to hurl boulders. The trailing edge of the storm, known as the riddens, consists of light rains mixed with relatively mild gusts of wind.  The Purelake experiences less intense highstorms.
When a highstorm and the Everstorm hits a location at the same time, the combined power of the storms can cause even greater destruction than normal, destroying the land below them with enough force to send boulders flying hundreds of feet up in the air.
On the Rosharan subastral of the Cognitive Realm, highstorms manifest in a non-violent manner, in contrast to its form in the Physical Realm. Instead of powerful winds and rain, the sky would simply light up, the clouds shimmering with a mother-of-pearl iridescence.
Stormwardens try to predict when highstorms occur, and have become somewhat accurate, though not always. The Stormwardens have negative connotations since predicting the future is forbidden under Vorin doctrine.
Vorin mythology claims that each storm is born in the east at the Origin before traveling west across Roshar, but modern Stormwardens believe there exists a single highstorm that travels around the planet, with the length between storms decided by the speed it travels during that time of year.
Highstorms are the single most important force in Roshar's ecology, and life on the planet has adapted to them. Some plants, like lavis polyps, enclose themselves against the highstorm's fury; others retract or fold their relatively fragile leaves, vines, or roots away. Many plants have outer coverings infused with highstorm crem, forming protective shells. Stormwarden's have discovered that Stormwater is better for plants on Roshar than regular water,, with crem providing nutrients that would otherwise be provided by soil swept away by the highstorms. Stormlight from gemstones infused during highstorms also helps plant grow.
Rosharan fauna has adapted as well; many species like axehounds, whitespines, and greatshells are covered in protective carapace. They also have gemhearts that glow with Stormlight, enabling their symbiotic relationship with spren.
People on Roshar live in cities and settlements that are protected from highstorms by natural or manmade structures. Kholinar has its windblades—large stone formations that divert the highstorm's force— and Sesemalex Dar has troughs that prevent the city from flooding. These structures are often city-wide and become an integral part of the city's culture.
Humans depend on highstorms not just for water, but also for the Stormlight that they use in their fabrials, the crem that they use as building material, and the regular weather patterns from which they base their calendars.
Other aspects of civilization are also affected by the highstorms. For example, sanitation regulations have been developed to prevent the trash of one town from being blown by the strong winds towards the next town. These regulations, however, do not apply on the Shattered Plains due to its isolated location, and so the refuse and litter of the Alethi warcamps there are piled high to be carried away during each highstorm.
Many curse words and insults are related to the highstorms, but they are also a target of reverence. The Stormfather is venerated by many. Some folklore traditions equate the Stormfather with the Herald Jezerezeh. Criminals have been known to be punished by being strung up outside during a highstorm in order to be "judged" by the Stormfather, who supposedly would let them live if they deserved it.
Highstorms are highly Invested, and are the primary source of Investiture on Roshar. Gemstones are infused with Stormlight when left outside during a highstorm. This magical source of illumination and power is used to Invest fabrials and Surgebinding. The strength of the storm is not tied directly to the amount of Stormlight invested into gemstones.
Another effect of a highstorm's Investiture is the crem in the storm water. This substance is deposited onto the land, accumulating over the millennia, even prior to the Shattering, It is currently unknown where crem comes from, but it partly contains minerals that are useful for plant life.
Several types of spren are associated with highstorms, most notably the Stormfather. Listeners can bond with spren during highstorms through a ritual that involves the Stormfather, who they call the Rider of Storms. He appears at a certain point during the storm, and somehow facilitates or enables the listener bond. The Stormfather also seems to have control over highstorms, able to send one at will.
Because of the strong winds, windspren are especially numerous during storms. Rainspren sometimes appear during the light rains of the riddens. More recently, stormspren have also started appearing.
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