Settings>Location>Privacy...
I turned off (or deselected rather) the location option for my weather app... Why? I don't know, but I did it.
Almost immediately after clicking the box next to it the app disappeared from the list (after the icon turned from its usual graphical identity to that little annoying dotted-line of a box). What should I do?
MacBook Pro with Retina display, OS X Mavericks (10.9)