Mariah is a character of the day who appeared in Foul Weather Friends. She also appeared in Ash & Pikachu.

A young meteorologist, Mariah has a weather station between Violet City and Azalea Town. She also keeps a cluster of Hoppip in a cage so she can study their behavior and movement to predict wind patterns. She believes Hoppip have some sort of sixth sense that lets them predict weather patterns early.

She also befriended an Oddish that believes itself to be a Hoppip and is trained to track down her seven Hoppip whenever they're blown away.

(Source: Bulbapedia)