Hi - "It HAS snowing this morning" isn't right (fantastic work, btw - I am loving the opportunity to learn Welsh, cough cough years after my classes at school)
Hi, there isn't a 'It has snowing....' in the course, unless this is some deleted sentence still appearing, which is a problem we're having with Duolingo at present.
Actually that may be a a symptom of a longstanding duolingo bug where "it's" is incorrectly considered to be interchangable with "it has".
Should at least have 'is' in there as a word option.
you hardly hear the "y", and "mae hi'n bwrw eira bore 'ma" should be acceptable, I think