"It is rainy today."
So for everyone who is confused (since Duolingo doesn't really explain): 雨 means rain and ふります means to fall. In Japanese there is no specific word for "snowing" or "raining". 雨がふります literally means "rain falls". So 雨がふりました means rain fell today, or it rained today. 今日は雨です means it was rainy today. Just like in English you could say "It was rainy today" Or you can specify "Today it rained". Hope that helps.
Yes, but just as in English you might say, "Rain today," instead of "rainy today," so can you in Japanese.
I think it has to do with 雨 being a noun. ふる means "to fall" so a combination is used to represent the action. my guess is 雨がふりました for past tense, someone correct me if I'm wrong.
It looks more like the difference between "it's a rainy day" and "it is raining" where you'd say 今日は雨がふります. The difference is emphasis.