noun
The ordinary word for day-to-day weather conditions, often used with 良い, 悪い, 予報, or verbs such as 確認する.
明日の天気を確認した。
I checked tomorrow's weather.
今日は天気が悪い。
The weather is bad today.
noun
In positive contexts, especially いい天気 or お天気, it refers to pleasant, fair weather rather than weather in general.
今日はいい天気ですね。
It's lovely weather today.
せっかくの天気だから、少し散歩しよう。
Since the weather is so nice, let's take a short walk.