NASA has published a tool to more accurately predict the sighting opportunities for the Shuttle Discovery along its landing path tomorrow morning (20 Apr 2010).  The instructions are here: http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts131/news/13…

and you can access the tool from this link: http://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaS…

Enjoy!