Perhaps Ophelia is operating under Heron's assumption that the sorcerer who killed himself in the barn wasn't making a permanent exit?
As for the spell 'predict weather' it will give you very precise information about the next twelve hours of weather - severity, temperature, precipitation amounts, etc., whereas your knowledge of woodcraft and natural phenomena can still give you a pretty good general idea about things - this is sort of equivalent to a farmer's intuition more than any kind of hard and fast rule. If you actually want to make a more detailed prediction without the spell I'll allow a simple saving throw.
FYI: Rhenmyr's woodcraft skills apply to his native terrain; in this case jungles and tropical areas, so he's out of his depth here.