noun
sun shower; sudden rain from a blue sky
Refers to rain falling while the sun is shining, often with no visible clouds. Sometimes associated with the folkloric expression 狐の嫁入り (kitsune no yomeiri, 'fox's wedding').
See also: 狐の嫁入り
天気雨が降ってきたので、虹が出るかもしれない。
A sun shower started, so a rainbow might appear.
晴れているのに天気雨が降る
It feels strange when it rains while the sun is out.
Compound of 天気 (tenki, 'weather' or 'fine weather') and 雨 (ame, 'rain'). The exact origin is uncertain, but it likely arose from the paradoxical combination of clear weather and rain.