Weather has a chance to change throughout the day
Still working out some bugs but, the current weather system in place in my game has a chance to change midway through the day. Basically there is a double roll for weather: one that's determines the morning weather, and then a second for the weather midway through the day. The second roll is locked to a certain range higher or lower than the original weather roll, so the weather shouldn't change *too* drastically (like if it's sunny, it isn't going to start storming).
And of course, the crops respond to the weather change. So check the weather or talk to NPCs before going through the trouble of watering all your crops first thing in the morning.