There is a question here on Meta on what is the distinction between folklore and mythology. The same question was raised on Area 51 Discussions before this proposal went into private beta.
I'm wondering if we should include folklore.
I agree that folklore should be included but wanted to elaborate on why a little bit.
Folklore and Mythology are inextricably linked. Formal mythologies developed from folklore and stories. There wasn't a day where someone said, oh by the way the skies and storms are controlled by Zeus. The likely scenario (the answer I would hazard is not truly known) is that people worried about storms, be it for travel or floods or ruining crops, putting a name to the phenomenon simply gives the people someone or something specific to pray to for relief.
This is difficult to answer because there really isn't a clear definition on what "folklore" actually is. In fact, the word wasn't even in large use until about 100 years ago. Your linked meta post goes into this well and one point that stands out as the difference between mythology and folklore is that folklore is about lesser individual things. There are stories about vampires, for example, but there is very little mythology of vampires and how they've interacted with other mythical characters or places over the ages. There are just isolated stories. There is no grander mythos that they belong to.
Folklore is certainly interesting, but it is not mythology and should not be on-topic. Mythology that appears to be folklore can be weighed against this scale:
If the answer is yes, then it is mythology not folklore and is on-topic, and so also are all the other related myths. If the myth revolves around a single figure or type of thing and does not belong to a greater mythos (collection of related myths), then is is folklore not mythology and is off-topic.
However, questions about how any folktales may have affected any mythologies is certainly on-topic and might prove to be a very interesting question source. But the reversely directed question is not on-topic, where the question is about how any mythology influenced any folktale because the folklore is the topic of the question, not the mythology.