depending on the weather
Used to express that something is conditional on weather conditions. Often appears in phrases like 天気次第で or 天気次第だ.
Tomorrow's picnic depends on the weather.
Whether the match is held depends on the weather.
次第 is a suffix meaning 'depending on' or 'as soon as'. 天気次第 is a specific compound using this suffix.
Compound of 天気 (weather) and 次第 (depending on).