Reference

Weather parameters

WeatherPreset is the whole weather as one JSON-safe object of thirteen numbers. Presets are WeatherPresets, set() merges a subset into the targets, and getParams() prints the complete set.

weather.params;                       // the targets (what presets and set() write)
weather.state;                        // the eased values actually used, plus gust and daylight
weather.set({ fog: 0.3 });            // subset, eased
weather.set({ fog: 0.3 }, { instant: true });
weather.getParams();                  // complete copy: targets + current wetness / snowCover, 3 decimals
weather.transitionRate = 0.4;         // slower easing (1/s, default 0.9)

#Precipitation and wind

Key	Range	`clear`	Effect
`rain`	0–1	`0`	Rain intensity: streak and splash count, fall speed, fog haze, wetting, audio
`snow`	0–1	`0`	Snowfall intensity: flake count, fog haze and height, snow cover
`wind`	0–1	`0.15`	Wind strength. `1` ≈ 13 m/s (47 km/h) before gusts
`windDirection`	radians	`0.6`	Direction the wind blows toward. `0` = +x, π/2 = +z. Wanders ±0.25 on its own

#Fog

Key	Range	`clear`	Effect
`fog`	0–1	`0.06`	Amount. Density ≈ `0.0015 + fog² × 0.11` per metre, plus rain and snow haze
`fogHeight`	≥ 0	`1`	Height-falloff multiplier. `0.3` is ground fog
`fogLight`	≥ 0	`1`	In-scattering multiplier

#Lightning

Key	Range	`clear`	Effect
`lightning`	0–1	`0`	Automatic strike frequency: every ~22 s at the low end to ~2.5 s at `1`. Off below `0.05`

#Surfaces

Key	Range	`clear`	Effect
`wetness`	0–1	`0`	Surface wetness to ease to over ~4.5 s. After that it follows the weather
`snowCover`	0–1	`0`	Snow cover to ease to over ~4.5 s. After that it follows the weather

These two aren't eased like the rest. set({ wetness }) calls weather.wetness.force(...), and with { instant: true } it calls setImmediate. Read the live values from weather.wetness.wetness and weather.wetness.snowCover.

#Sky hints and exposure

Key	Range	`clear`	Effect
`cloud`	0–1	`0.15`	Suggested cloud cover for your sky. `state.cloud` is raised to at least `rain × 0.9`, `snow × 0.8` and `lightning`
`time`	0–24	`14`	Suggested time of day in hours, for your sky. Eases the short way round the clock
`exposure`	> 0	`1`	Multiplier for `weather.render()`'s exposure

The library doesn't draw a sky, so cloud and time only matter if you read them. The demo sky reads weather.state.time and weather.state.cloud. cloud also slows drying in the sun.

#Derived state

weather.state holds the eased copy of every key above, plus:

Key
`gust`	Gust factor, 0.5–1.2, multiplied into the wind speed
`daylight`	0 at night … 1 by day. From `setLighting({ daylight })`, or from the key light's height
`wetness`, `snowCover`	Mirrors of `weather.wetness.wetness` and `.snowCover`

The wind vector actually used, in m/s, is weather.uniforms.wind.value (x, 0, z).

#Easing

Every frame, each eased key moves toward its target by 1 − exp(−dt × transitionRate). With the default 0.9, a change is about 60 % done after a second and 93 % after three. time eases at its own fixed rate of 1.2. { instant: true } skips the easing.