I've heard some trials require Day/Weather against mobs that cannot be under said weather and give exp. [Without sync.]
Haven't run into any myself, but I fear that day.
Hunting large amounts of mobs on one day of the week would be a pain.

We need weather in more places, and more frequently.
Maybe a way to predict weather better, would be nice. (Ex: Magian Specs tell you what time of day to expect weather.)