why is "before the better weather" not accepted? Is it because "wella" is acting as a verb in this sentence?
Gwella is the verb-noun 'improving, to improve'. The adjective is gwell - 'better'.
- Cyn i'r tywydd wella - Before the weather improves
- Cyn i'r tywydd gwell ddod - Before the better weather comes.
The mutation of the verb-nouns is caused by the cyn i pattern, not by the masculine noun tywydd.