I have a better idea. Weather could change you motivation towards different jobs and would also make them more dangerous or impossible to do, for example you can't raft wood if the lake is frozen.
If you're going to make some jobs impossible to do, you might as well give bonuses to others.
It is raining: "It is favorable for tending pigs in this weather"
As stated above, more water softens the mud in the pig pens, and there is a better chance of the pigs dying from sickness or mud slide, which means better chance at getting ham.
Other things like cash, luck and experience depend on different things. More cash for risking your health in the weather, or less cash because you could not do the job as well as you ought to have done. More experience for doing the job in harder conditions, or less experience from being too distracted by weather. More luck of finding random items from kicking up all the dirt, or less luck for finding random items because you can't see in all this rain. Etc.
