Wikis / MythicSeasons / Atmosphere / Weather

Weather

weather in atmosphere.yml decides when simulated air counts as rain, snow or a storm. biome-defaults turns the vanilla biome under each cell into its climate.

Every key can also be set per season, world or profile (see Overrides) and applies on /ms reload. Values outside the range move to the nearest end without a message.

Rain, snow and storms

Option Default Range What it does
rain-precip-threshold 0.15 0 to 100 Rain intensity needed before players see rain. The built-in value is 0.12.
snow-temp-threshold 0.5 -60 to 60 Ground air temperature in degrees C below which rain falls as snow.
storm-precip-threshold 0.5 0 to 100 Rain intensity needed for a storm.
storm-updraft-threshold 2.5 0 to 100 Updraft in m/s that some level above the spot must also exceed for a storm.
Weather Needs Players notice it as
Rain Rain intensity above rain-precip-threshold and cloud above the player Client rain, atmosphere{raining=true}, the triggers atmosphere-rain-start and -stop
Snow Rain, with ground air below snow-temp-threshold atmosphere{snowing=true}, the snow triggers, the snowflakes of the bundled skill MS_AtmosphereSnow
Storm Rain intensity above storm-precip-threshold, an updraft above storm-updraft-threshold and cloud above the player Thunder while it rains, atmosphere{storm=true}, the storm triggers, darker cloud
  • "Cloud above the player" means drawn cloud of the first solid (opacity 1) cloud layer. Drizzle from low cloud under that layer's floor or from ground fog is not shown. Without a solid layer, a player above the top of the simulated cloud gets no rain.
  • <mythicseasons.precipitation> reads the rain intensity, and the Rain: or Snow: line of /ms atmosphere stats shows it above rain-precip-threshold (none below). It tops out at 8 in steps of about 0.031, so two thresholds between the same two steps behave the same.
  • Outside naturally cold biomes the client draws rain, so the bundled skill adds the snowfall.
  • Thunder is only sent while it also rains for that player, so a storm-precip-threshold below rain-precip-threshold gives storms that do not thunder until rain shows.
  • Weather spots set through a land plugin win inside their area. Where the simulation has no answer, such as a world without it, the server's weather answers and the weather triggers stay quiet.
  • The shipped seasons set rain-precip-threshold to 0.18 in spring, 0.26 in summer and 0.09 in winter. Fall keeps 0.15.

Snow on the ground

The simulation keeps a snow cover from 0 (bare) to 1 (full) for each spot, and a season populator with use-snow-coverage: true puts snow on that share of the ground. Times are weather minutes (30 are 7.5 real minutes at the default timing).

Option Default Range What it does
snow-cover.build-minutes 30.0 0.1 to 10080 Snowfall from bare ground to full cover.
snow-cover.rain-melt-minutes 60.0 0.1 to 10080 Rain from full cover to bare ground.
snow-cover.thaw-minutes 120.0 0.1 to 10080 No rain and ground air at or above snow-temp-threshold, from full cover to bare ground.

Biome climate

Each cell takes its climate from the vanilla biome at the surface of the nearest loaded chunk:

  • temperature (degrees C) = vanilla temperature x temp-scale + temp-offset
  • moisture (g/kg) = vapor-base + vapor-scale x vanilla downfall

The ground air moves toward these values, shifted by the season and the time of day. The vanilla temperature is limited to -0.7 to 2.0. The Biome: line of /ms atmosphere stats shows the biome and base temperature where you stand.

Option Default Range What it does
biome-defaults.temp-scale 18.0 -1000 to 1000 Degrees C per unit of vanilla temperature.
biome-defaults.temp-offset -2.0 -1000 to 1000 Degrees C added to every biome.
biome-defaults.vapor-base 2.0 0 to 40 Moisture in g/kg of a biome with no downfall.
biome-defaults.vapor-scale 10.0 0 to 100 Moisture in g/kg per unit of vanilla downfall.

A plains biome (temperature 0.8, downfall 0.4) gets 0.8 x 18 - 2 = 12.4 C and 2 + 10 x 0.4 = 6 g/kg. Warm air holds more moisture before cloud forms (about 14.5 g/kg at 20 C), so hot seasons need a higher humidity to rain at all. A cell no loaded chunk has sampled yet takes the average of the sampled cells in the simulated area.

Per-biome offsets

A biome file in the biomes folder can add local weather for its biomes with an atmosphere: block:

atmosphere:
  temp-offset: 0.0
  vapor-multiplier: 1.0
  seasons:
    summer:
      temp-offset: 2.0
      vapor-multiplier: 1.2
    winter:
      temp-offset: -3.0
      vapor-multiplier: 0.7
  • temp-offset adds degrees C (default 0) and vapor-multiplier scales the moisture (default 1). An entry under seasons, by season id, replaces them for that season.
  • Only cells with a terrain sample get an offset, picked by the biome of that sample. With the cloud layer on, new offsets apply after /ms reload.

Examples

weather:
  rain-precip-threshold: 0.25

Only heavier rain is shown.

atmosphere:
  weather:
    snow-temp-threshold: 2.0

In a season file: rain falls as snow when the ground air is below 2 C.

biome-defaults:
  temp-scale: 12.0
  temp-offset: 0.0

A milder world: plains get 0.8 x 12 = 9.6 C instead of 12.4.

Updated Nov 11, 2026