Strong Air Runes need a Skystone along with a Blank Rune; a Silver Ingot and three Normal Air Runes to make one Strong Air Rune.
Strong Runes can be crafted at level twenty at the Rune Altar.
You need three of these to learn Tornado Storm and you will need extra to cast the spell.
The command to make a Strong Air Rune is [nya!rpg rune altar strong air]. For more info use [nya!info strong air rune].