I noticed that a couple winter textures stand out of the rest too much:
- Conifers seem to reuse summer texture, when imho they should get a bit "duller" in winter.
- Grass runways seem to keep their summer texture, which is dirt for low shader level and grass for high shader level.
Example: --airport=EDHE --season=winter
ALS keeps track of the snow level separately through the "Climate" dialog, so I think the separate winter textures are largely unmaintained.