今天天晴。

Jīntiān tiānqíng.

It's a clear day today.

今天一整天都是晴天。

Jīntiān yì zhěngtiān dōu shì qíngtiān.

The weather was nice all day today.

今天是晴天，天气很好。

Jīntiān shì qíngtiān, tiānqì hěn hǎo.

Today is a sunny day, the weather is very good.