Storm Feather
Storm Feather is a Fletching material. 
Tempest Roc (combat level 99) drops it on every kill. It goes into 
Storm Arrow (Fletching level 90), and the quest Rangers' Guild Trials asks for it. It sells for 100 gp.
Obtained from
Monster drops — Tempest Roc — 100%
Used in
Fletching — Storm Arrow (×5)
Quest — Rangers' Guild Trials (collect 18,000)
Related items
- Same family:
Polished Feather, 
Golden Feather. - Also dropped by Tempest Roc:
Big Bones, 
Dragon Arrow, 
Rune Arrow, 
Mithril Bolt, 
Adamant Bolt, 
Rune Bolt, 
Dragon Bolt, 
Mithril Arrow.