Snowfall

Snowfall is a type of weather that occurs occasionally in Minecraft.

Behavior
Snowfall is a temporary, biome specific occurrence that can happen randomly at any time in cold biomes, and above a certain altitude, within the Overworld. In hot/dry biomes, and in other dimensions, it does not snow at all.

The average snowfall lasts 0.5 – 1 Minecraft day, and there is a 0.5 to 7.5 day delay between snowstorms. Snowstorms have a small chance to worsen into thunderstorms.

Snowstorms can be skipped entirely with the use of a bed.

Effects


Snowstorms darken the world, causing the light from the sun to decrease by 3, bringing it to light level 12 in full daylight. Moonlight, however, is not reduced, and remains at light level 4. The sky itself will darken (even in biomes where it does not snow), to the point where celestial bodies (the sun, moon, and stars) are no longer visible. The clouds darken from white to a light gray, although clouds themselves do not precipitate. Although the sun is not visible during snowfall, the glow associated with sunrise and sunset is still visible.

As it snows, snow layers regenerate over all non-transparent blocks. In Pocket Edition, these snow layers will accumulate and grow over time.

Snow particles
Falling snowflake particle effects are visible through the air over all cold regions. Unlike with rain, any entities that are on fire will not be put out on contact with snow. Note that snowflakes only fall in the two middle lines of a block, thus will not visibly fall directly onto the player.

Snowflakes fall through ladders, vines, carpets, redstone repeaters, snow layers, mob heads, flower pots and cobwebs. They are stopped by signs, banners, doors, fence gates, trapdoors, pressure plates, glass panes and iron bars.

Trivia

 * Snow actually falls one block into the void (Layer -1). This can be seen by digging a vertical shaft down in Creative mode, removing the bottom layers of Bedrock, and flying down into the Void. Note that no particles are emitted from the snow, due to the absence of a block below it.
 * Snow still falls above the clouds. Notch's explanation is that the gray above the clouds during a storm is another layer of clouds and the origin of the snow.