Ice and Snow

Ice is generated during the terrain shape stage anywhere the temperature is less than 0.5. However this does not line up completely with the later determined biomes, which then determine where ice and snow can form via Random Ticking.

Unticked Ticked
Generated without random ticks Generated with random ticks

This becomes more apparent when the relevant values are visualized.

Biomes (Map Colors) + Temp < 0.5 (Red)
Biome map with Map colors, Red marking where temperature values are less than 0.5

Biome map with Map colors, Red marking where temperature values are less than 0.5

Snow depends on the same system to determine where it can appear, though its placed later in the population stage.

Seed for this section is -1712183887779554298, showing the area around chunk x: -1, z:6