Shouldn't it be cymylog?
In this usage, the 'n/yn causes a soft mutation of the adjective which follows, so cymylog -> gymylog
More info about the various usages of yn here - https://www.duolingo.com/comment/13844144
Surely it should translate to "It was" cloudy not "It has" cloudy
Mae hi'n... - 'It is...'
It says "It has cloudy" when it should be "It was cloudy"
This seems to be a bug in Duo at the moment.