Current location's weather condition can be shown in both Celsius and Fahrenheit unit on Galaxy lock screen. To see weather on lock screen in Galaxy S3 do as follows:
1. Open "Settings" app and then go to "Lock Screen"
2. You need to set the screen lock to Swipe, to see weather condition on lock screen
3. Tap "Lock Screen options"
4. Enable "Weather"
5. Tap "Weather" to customize the unit (Celsius or Fahrenheit) and change update Auto refresh time (From every 1 hour to every 23 hours)