Look out the window! It is snowing right now.

We use "it" as an empty (or "dummy") subject to talk about the weather. We cannot use "there" or personal pronouns like "he" or "she" for weather.

Yesterday, it was so windy that my hat flew away.

Even in the past tense, we use "it" (it was) to describe weather conditions.

I just hope it is sunny tomorrow so we can finally go to the beach.

We continue using "it" for future or hoped-for weather.