by Gijs » Wed Feb 15, 2012 11:06 am
The "snow line" option only affects shaders. Not all terraintypes have shaders assigned in 2.4.0 (IIRC; in 2.6.0 it's better). The snow you see in your first picture is part of the texture (FlightGear switches to "winter" textures when you set the season). You might even get a better result setting the season to summer and then adjusting the snow line...
Airports: EHAM, EHLE, KSFO
Aircraft: 747-400