If I was to do this, I would start by investigating the available API from wunderground.
Then I would look for similar projects in order to get inspiration.
When it comes to language, it mainly depends on your level of skill.
C is not that hard, but you need to understand what a pointer is and you might want to find some libraries to use in order to avoid doing everything from scratch.
Python makes it easy to work with JSON, lists, sets, etc., but it will consume some extra space.
If you select Python, you don't have to worry about cross compiling, so it might be easier to start with.
So instead of asking which language is better (which basically can be compared to asking which religion is better, which of course depends on personal preferences), it is better to ask "In which language will it be easiest?".
I write this because I assume you are new to programming, and writing in C might kill your motivation if the task is too complex.
I hope this helps.