The uncanny valley is a term used to describe systems that act and sound like humans, but are somehow slightly off. This slight discrepancy actually leads to the bot feeling a lot more unnatural, and this is the exact opposite of what we are trying to accomplish with natural language generation. Instead, we should avoid trying to make the bot perfect in its natural language responses; the chances of finding ourselves in the uncanny valley get higher the more human-like we try to make a bot sound.
Instead, we should focus on making our bots useful and easy to use, over making its responses natural. A good principle to follow is to build your bot to be as smart as a puppy, a concept championed by Matt Jones (http://berglondon.com/blog/2010/09/04/b-a-s-a-a-p/):
"Making smart things that don't try to be too smart and fail, and indeed, by design, make endearing failures in their attempts to learn and improve. Like puppies."
Let's expand our weatherbot to make the generated response...