Climora

v0.1 - First Front

Added

Climate grid

• The world is divided into weather cells of 128×128 blocks (8×8 chunks). Cells around players are built from the biomes and terrain underneath them and simulated on the server without loading chunks.
• Every dimension with an open sky gets its own simulation — the Overworld and modded dimensions like it. The Nether and the End have no weather.
• Values are blended between cell centres, so temperature, wind and rain have no steps at cell borders.

Temperature

• Air temperature in °C, from the biome, the elevation and the time of day. Roughly 3 °C colder per 100 blocks of altitude.
• Every vanilla Overworld biome has its own profile: a daily mean, a day/night swing and a humidity. A desert reaches about +38 °C by day and drops to +14 °C at night, because dry air loses heat fast; a jungle stays warm and humid around the clock with a swing of only ±5 °C; the sea barely changes at all.
• Mountain biomes are cold in their own right — their profile is defined at mountain height, so peaks are not cooled twice.
• Neighbouring cells exchange heat, and clouds damp the day/night swing.

Pressure and wind

• Highs and lows a couple of kilometres across drift across the world. They depend on the world seed and travel with the prevailing flow, taking about one in-game day to pass overhead.
• Wind is computed from the pressure gradient — out of highs, into lows — plus the steering flow that carries the weather systems. Gusts pick up in thunderstorms.
• Wind carries moisture and clouds, so weather arrives from upwind.
• Rain leans and snow drifts with the wind.

Moisture, clouds and precipitation

• Air takes up moisture from the biome and from nearby water; rising air in a low collects it and lifts it.
• Cloud cover and rain grow out of moist rising air. Deserts almost never see rain, jungles often do.
• Rain falls only where the simulation puts it, and it has edges. The sky is always overcast where it rains.
• Clouds are drawn from the simulated cover instead of the vanilla texture: block-shaped like vanilla, but only where there are clouds. Rain clouds sit lower and thicker, storm clouds grow into tall towers.
• Clouds drift with the weather systems and look the same for every player on a server.
• Rain or snow is decided by air temperature, not by the biome, so it snows above the freezing line in mountains that would rain lower down.

Thunderstorms

• Storms form on their own where warm, very humid air is forced upwards, either by a low or by afternoon heating. The sky darkens, clouds tower, wind turns gusty.
• Lightning strikes only inside storm cells and only where rain is falling. Lightning rods and target selection work as in vanilla.

Snow and ice

• Snow builds up in layers while it is snowing.
• Still water freezes at the edges when the air is below −1 °C.
• Snow and ice melt anywhere warmer than +1 °C, including in the dark. Vanilla needs bright light to melt, which is why snow in shade used to last forever.

Weather vane

• A block crafted from 4 copper ingots and an iron ingot. Its arrow turns to face the wind and sways in the gusts.
• A comparator next to it reads the wind speed on the Beaufort scale as a signal of 0–15.

Vanilla integration

• Local weather drives the vanilla systems: mobs get wet, fires go out, cauldrons fill, snow settles.
• Vanilla /weather clear|rain|thunder turns on local weather within about 4 km of the player. This can be switched off.

Commands (permission level 2)

• /climora temperature [pos] — air temperature at a position.
• /climora cell [pos] — the state of a weather cell: mean temperature, daily swing, pressure, humidity, cloud cover, precipitation.
• /climora weather clear|cloudy|rain|storm [radius] [seconds] and /climora weather auto.
• /climora stats — cell counts and simulation load.
• /climora resample [radius] — rebuild cells from the terrain, needed after changing biomes with /fillbiome.
• /climora stress <radius> — load test.
• /climora reload — reload the server config.

Configuration

• config/climora.json for the server, reloadable with /climora reload, and config/climora-client.json for the client.

Debug

• An F3 overlay with the air temperature at the player, the cell's state and the simulation load. Works in singleplayer and on servers running the mod.

Technical notes

• Built for Minecraft 1.21.1 on Fabric and NeoForge from one codebase, through Architectury.
• Climate is stored per dimension in data/climora_climate.dat, data format version 4.
• The server sends each player the weather of the 7×7 cells around them once per second, about 500 bytes. The client eases towards each update over a second.
• The simulation runs inside a 1 ms per tick budget and stays around 0.015 ms in practice. Cells are updated round-robin, and the relaxation is exact for a step of any length, so a cell that has not been touched for a while catches up in a single update.
• F3 data is only sent to players with the debug screen open, and never when reducedDebugInfo is set.