Polite noun for weather, used in everyday conversation. Often used in set phrases like お天気がいい (the weather is nice).
See also: 天気
The weather is nice today, isn't it?
What's the weather like tomorrow?
Refers to someone's mood or temper, often used in the phrase お天気屋 (a moody person). This sense is less common than the weather meaning.
He's moody and sometimes suddenly gets into a bad temper.
The weather is nice today, isn't it?
We were blessed with good weather on our wedding day.
Whether we can go on the outing depends on the weather.