You can head over to world.cfg and find this:
virtelev = (virtual_elevation) {
virtelev = (float2) {
x = 3500.0,
y = 0.0
},
virtcurv = 5000.0,
snowmin = 4900.0,
snowsat = 6000.0
}
Snow is generated from snowmin elevation, full snow is at snowsat elevation. The elevation is virtual, equals the real one only at the equator normalized on the equator, and with rising latitude it gets higher by virtelev.x*cos(lat) + virtelev.y*cos^2(lat)
To make it work with day of year, we have to use virtual latitude, taking the current inclination angle into the account.
