"The weather is nice today."
"The only lesson you will ever need" が vs は
[excerpt from description] Learn the DIFFERENCES between the は (wa) particle and the が (ga) particle! ★ The differences ☆ When to Use / How to Use ★ What they mean
☆Did you know that using the は particle instead of the が particle could be VERY rude and offend the listener?? × 笑顔は素敵ですね。(egao WA suteki desu ne) = Your smile is nice ....BUT!!!!
今日の天気 would make "the weather of today" the subject, where as 今日は天気が makes "today" the subject and "weather" what is being said about "today". May seem like the same thing, but if you were to change the nouns the whole meaning changes. Example: ひとみの自転車は好きです means "I like Hitomi's bicycle", whereas ひとみは自転車が好きです means "Hitomi likes bycicles". Hope it helps.