Ann means there --"there is frost." See the tips and notes, here: https://www.duolingo.com/skill/gd/Rain/tips-and-notes
a-nis - now in the general sense, could mean today compared to yesterday
an-dràsta - now in the sense of "this minute"; you'll also see it as "just now"
Another expression is, an-dràsta fhèin. That is just a more intense version, it's like, "right now, this very second"