Fine or fair weather: clear, pleasant conditions (often said as 'ii tenki' in casual speech), suitable for outdoor activities.
今日はいい天気だから散歩に行こう。
The weather is nice today, so let's go for a walk.
明日は良い天気が続く予報だ。
The forecast says fair weather will continue tomorrow.
ピクニックにはよい天気が必要だ。
Good weather is necessary for a picnic.