Forecast

Forecast changes both the type and form of the Pokemon based on the current weather condition. In rain, it becomes Water-type (Rainy Form). In harsh sunlight, it becomes Fire-type (Sunny Form). In hail or snow, it becomes Ice-type (Snowy Form). Under any other condition — including sandstorm, no weather, or if weather effects are suppressed — it reverts to Normal-type (Normal Form).

The form and type change occurs instantly whenever weather changes, and it reverts immediately if the weather ends or is nullified by Air Lock or Cloud Nine. Forecast only works on Castform specifically — if another Pokemon obtains this ability through Trace or Skill Swap, it will not change their type or form.

Forecast is the signature ability of Castform, introduced in Generation III. While conceptually interesting, Castform's base stats are modest, limiting its competitive viability despite the type-shifting versatility. The ability demonstrates how weather conditions mechanically interact with Pokemon identities.