Weather system

APLM’s weather system is per-material, not global. Every biome and every base layer carries its own weather toggle and its own response curves. A Tropical Rainforest can be drenched in rain while a nearby Desert stays dry in the same tick. The system runs through MPC_Weathers and is configurable from Blueprint through BP_APLMController.

What every layer exposes

Each material group in the Material Instance has a Weather category with three core controls plus surface-specific tuning:

Parameter	Effect
bEnableBiomeXWeather or bEnableBaseXWeather	Master toggle for this layer’s weather response.
Biome_X_R_PSt or Base_X_R_PSt	Rain intensity for this layer, configured in MPC_Weathers.
Biome_X_S_PSt or Base_X_S_PSt	Snow intensity for this layer, configured in MPC_Weathers.

X is the layer name (Tundra, BorealForest, Desert, and so on for biomes; Beach, Cliff, Grass, Gravel, Mud, Snow for base).

Wet surface tuning

When a layer’s weather is enabled, several surface parameters become active. They control how the wet look reads on screen:

Parameter	Effect
WaveUVScale	Scale of the rippling water surface that appears in puddles.
WaveNormalIntensity	Normal intensity of that surface.
WaveUVSpeed	Animation speed of the wave UV.
RippleStrength	Strength of raindrop ripples.
RippleScale	Size of the ripple pattern.
RippleSpeed	Ripple animation speed.
WaterPuddleTilling	Tiling for the water puddle mask.
RainMudPuddleTilling	Tiling for the rain mud puddle mask.
SnowPuddleTilling	Tiling for the snow puddle mask.
SnowMudPuddleTilling	Tiling for the snow mud puddle mask.

The split between water puddle, mud puddle, and snow puddle gives you separate art-direction control over each kind of wet surface.

Why per-material weather

Two reasons.

First, ecosystems are not uniform under the same sky. Sandy desert dries fast, jungle floor stays wet, snow pack does not turn to mud the moment it rains. Per-material weather lets the surface response model that.

Second, you can use weather as an art-direction control without simulating real weather at all. Pin a single biome’s rain to 1.0 to give a region a permanently wet look, regardless of what your sky system is doing.

Tip

Pair APLM’s per-material weather with a sky/weather plugin (Meridian Sky Engine, Ultra Dynamic Sky, or a custom system) by writing the global rain and snow values from that system into MPC_Weathers once per tick. APLM does the rest.

Where to next

• Weather parameters reference: the parameter table without the prose
• Special parameters: puddle and gravel-blend parameters that interact with weather