Strong Air Runes need a Skystone along with a Blank Rune; a Silver Ingot and three Air Runes to make one Strong Air Rune.
Strong Runes can be crafted at Arcane Forging 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 [@Neko Chan#7837 rpg rune altar strong air].
For more info use [@Neko Chan#7837 item info strong air rune].