I’m still struggling to work out whether your problem is due to some technical issue or just a misunderstanding of how seasonal assets work in Trainz. In case it’s just misunderstanding, I’ll elaborate on how Trainz handles seasons and snow. Everything that I say below assumes that the assets involved have been equipped with the relevant textures and have been configured correctly according to Trainz seasonal effect conventions.
Snow on/off is always a binary choice for season-enabled assets. Whether they be ground textures, tracks or scenery such as buildings or trees, snow in Trainz only depends on the altitude of the asset relative to the snowline height value that you set in the Environment tab. It also does not depend on the month, or the location of the world origin.
If the asset is above the snowline: Snow will be ON and any month-based effects (like autumn, winter, spring and summer textures on trees) will not be seen. It will just be snow, whatever the time of year, and all through the year. This actually conforms to the real-world definition of snowline. If seasonal things aren’t displaying snow, then lower your snowline setting until they do. You can use negative numbers to force snow textures if your ground altitude happens to be 0. Tip: use snowline settings that are at least 10m lower than the altitude you want the snow on/off transition to occur at (to allow a bit of error margin for the process).
If the asset is below the snowline: Snow will be OFF and only then can you see any month-based texture changes, such as in seasonal vegetation. The month-to-month timing (the phase) of those changes is determined by the world origin location - specifically, what counts is whether it’s in the southern or northern hemisphere. For example, if it’s in the southern hemisphere, autumn textures should appear in March to May, but if the origin is in the northern hemisphere, autumn should be in September to November. In other words, the seasons are 6 months different in the two hemispheres. The exact latitude or longitude of the origin has no effect on seasonal phasing, except to say that in Trainz, the equator is deemed to be part of the northern hemisphere. Latitude does affect the height of the sun's daily arc in the sky (and therefore the lengths of shadows).
Buried in all those words is one perennial source of confusion, which may be important for your understanding. The months defined as winter in Trainz are not synonymous with snow. For a Canadian this can seem counter-intuitive, even annoying, but it is how Trainz allows for parts of the world where so-called winter months never produce snow (think of Bermuda). You can expect some seasonal trees to be bare in winter months, some ground textures to be rather dull colours, but they should not be automatically covered in snow just because of the time of year, in Canada or anywhere else. The only way to get any seasonal asset to show snow textures should be to lower the snowline setting until it forces snow to appear.
From all that, you can see that you can force snow by adjusting snowline to a lower elevation, but you need to remember to adjust it back upwards if you want to see the other non-snow seasonal texture schemes.
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