Knife Storms are similar to normal storms, but instead of water, daggers rain down. One occurs in the episode "Rainy Day Daydream." They are apparently rare, as Finn claims never to have seen one before (though Jake already knew what it was). Right before Jake pulls him into the Tree Fort for shelter, Finn calls the storm "beautiful." A knife storm also occurs in the episode "Puhoy" (three years later in-show).
In both occasions, Finn and Jake are confined to their Tree Fort, forced to come up with ways to pass the time. In "Rainy Day Daydream," Finn and Jake use their imaginations to create a Bazooka Goblin, a Riddle Master, an Imagination machine, and more. In "Puhoy," Jake builds Finn a pillow fort during the storm, unknowingly giving Finn access to Pillow World.
- The storm appears as a game feature in the games Finn and Jake's Epic Quest, Adventure Time: Hey Ice King! Why'd you steal our garbage?!!, and Fionna Fights!
- Knife storms can form very quickly: in "Rainy Day Daydream", it took about ten seconds to start.
- Somehow there seems to be no visible damage on the tree fort except on the bridge while the storm is occurring.