The Storm Card has the ability to create huge rainstorms and tornadoes. It is related to The Rain and The Cloud Clow Cards, possibly like how The Big is related to The Little. The Storm's true form looks like a little girl with her hair styled in drill-like curls and wears spiked battle armor. It is under The Windy.
The Storm first appers is Episode 15. It was captured in the beginning of the episode when Syaoran attacked the eye of Storm's storm with a lightning spell, which is its weak point. Since he was the one to draw out the true form of the card, he became its master after Sakura sealed it.
Neither Syaoran or Sakura (after she became the mistress of all the Clow Cards) were seen using it in the series, but its most notable appearance was in the first movie. It was when Syaoran used Storm to distract Madoushi, allowing Sakura to escape.
The Storm was transformed into a Sakura Card in Sakura Meets Clow Reed (Episode 69). It was transformed along with the few remaining Clow Cards.