Quickly I have two ideas.
The first one correspond to a Silverlight page:
You can add a parameter in your querystring (on your first screen page) in your silverlight application. In the other Page you get the value of the querystring variable.
The second solution, if you use usercontrol, is more simple:
You need to pass the parameter (city for eg.) of the first screen, inside the constructor of the second screen.
public SecondScreen(int cityID)
Hope it helps. :)