Second tier storm spells provide the double weather effect. This does not stack with current weather.
Dusty weather has a chance (33% to 50%) to give earth spells a 25% power boost and a corresponding penalty to lightning spells. If Dorin Obi or Hachirin-no-Obi is equipped, the weather bonus will always be applied.
Geohelix will always gain the weather damage bonus.
Sandstorm will trigger the latent effect on equipment such as the Desert Boots (+12% movement speed in sandstorms), despite the fact that normally "sandstorms" only refers to the double weather effect (as referenced by Weather NPCs).
How to Obtain