The app has a clean UI... but perhaps "too clean". We could use some options, such as to change from English to metric or Fahrenheit to Celsius, to disable/enable the background image, toast notifications, etc. Also, the live tile could be improved.
I liked the charts and graphs, though. Just add customization options (the spirit of the Windows Phone experience) would push your app several notches higher. I'm keeping your app installed (along with ~20 other weather apps), but I would have to disable it from running in the background and unpin it from the start screen for now.