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All the rendered/heard weather effects: particles, lightning, wind systems, and sounds. For per-material weather (wetness/snow coverage on surfaces), see udw-material-and-screen-effects.
System
Driven by
Category on UDW
Rain Particles
Rain value
Rain Particles
Snow Particles
Snow value
Snow Particles
Dust Particles
Dust value
Dust Particles
Shared particle settings
All particle systems
Shared Particle Settings
Lightning Flashes
Thunder/Lightning value
Lightning
Obscured Lightning
Thunder/Lightning value
Lightning
Wind Direction
Wind Direction Basic Control
Wind Direction
Wind Gusts
Wind Intensity value + perlin noise
Wind Gusts
Wind Debris
Wind Intensity value
Wind Debris
Wind Directional Source
Wind Intensity + Direction
Wind Directional Source
Wind Physics Force
Wind state per actor
(component class)
Wind Camera Shake
Wind Intensity
Wind Camera Shake
Weather Sound Effects
Wind / Rain / Thunder values
Sound Effects
Sound Occlusion
Player Occlusion (on UDS)
Sound Occlusion
Environment Sounds
Time / Weather / Wind (via metasound)
Sound Effects
When to use this skill
Rain or snow not visible, or visible where it shouldn't be.
Choosing between particle collision modes for perf vs flexibility.
Lightning bolts striking specific actors as game logic.
Adding wind force to physics objects or making chaos cloth react.
Weather sounds going quiet at wrong times.
Adding ambient outdoor audio (birds, insects, city) that changes with time/weather.
Diagnosing VR splash particles only rendering in one eye.
Rain / Snow / Dust Particles
Three per-particle categories on UDW: Rain Particles, Snow Particles, Dust Particles. Each is controlled by the corresponding weather state value.
Category
Specific extras
Rain Particles
Splash particles (raindrop impacts on collision surfaces); color + lighting + max count
Snow Particles
Particle scale + max count + ambient light intensities
Dust Particles
Particle scale + color + alpha + max count
For shared behaviors (collision and spawning), see Shared Particle Settings below.
Splash Particles in VR
Symptom
Cause
Workaround
Splashes render only in one eye
Instanced Stereo doesn't support GPU sprites with deferred decal materials (the default splash setup)
Set Splash Particles Rendering Mode to Translucent. Renders in both eyes; subject to translucent lighting limitations.
Weather Particle Collision
Set with Particle Collision Mode.
Mode
Cost
Flexibility
Best for
Simple Collision
CPU cost (significant)
High — uses level simple collision
Default; need precise blocking
Distance Field Collision
Cheap on CPU (pure GPU)
Limited — can't separate from distance-field lighting
Open worlds with distance fields
No Collision
Cheapest
None
Diagnosing "particles aren't visible"
Simple Collision details
Line traces against simple collision geometry of the level. The particles trace on one channel — Weather Particle Collision Channel (default: Visibility).
Niagara particle traces are queries — meshes need queries enabled on their collision response.
GPU particles take a small number of valid particle paths and reuse them — still can be a significant CPU cost.
Particles not blocked when they should be (Simple Collision):
Object lacks simple collision geometry. Traces only check simple collision.
Collision profile isn't set to block the channel selected on UDW (default Visibility), with collision response Collision Enabled or Query Only (Niagara uses queries).
Particles coming through a high ceiling: raise Ceiling Check Height on UDW.
Distance Field Collision details
Pure GPU emitters querying the global distance field.
Constraint
Detail
Requires project to generate mesh distance fields
Project Settings
Distance field collision and lighting can't be separated
Surface that blocks particles also affects distance-field lighting; vice versa
Only works while global distance field exists
Engine scalability can disable it
Particles not colliding (Distance Field):
Project not generating mesh distance fields.
View Show → Visualize → Global Distance Field to see what particles actually see.
For meshes that should block, enable Affect Distance Field Lighting.
Blocking particles without a mesh
UDS Occlusion Volume actor at Blueprints/Occlusion/ — enable its setting to block weather particles. Only available with Simple Collision mode.
Latency-free per-sphere blocking
For a moving space where particle collision latency is a problem (e.g. a player vehicle interior):
Component
Effect
Weather Particles Kill Sphere
Kill any weather particles inside the sphere with zero latency
Only one Kill Sphere can be active at a time globally. Manage activation/deactivation manually for multiple.
Shared Particle Settings (Spawning)
In Shared Particle Settings. Particles spawn only in a volume around the camera; the illusion is they spawn everywhere.
Setting
Effect
Max Spawn Distance
How far from camera particles spawn (X/Y)
Spawn Distance Distribution
How particles distribute within that range
Spawn Box Height
How far above camera particles can spawn
World Spawn Offset, Camera Forward Spawn Offset
Relocate the center of the spawn area
Custom Weather Particle Camera Transform(advanced dropdown)
Spawn around a manual location instead of the camera
Particles Not Visible
Cause
Fix
Particles blocked by an invisible collision source
Switch Particle Collision Mode → No Collision to test
Editor viewport Show flags hiding sprites
Show dropdown → Use Defaults
Rare engine bug: Niagara compilation failed on first load
Open system asset in Particles/ (Rain/Snow/Dust) → Compile dropdown → Full Rebuild
Running in Simulate play mode
Limitation: it renders through editor camera and neither the blueprint or Niagara can sample the editor camera for the particle spawn area. Use a different play mode.
Lightning
Two types:
Type
What
Setting
Lightning Flashes
Big bolts that cast light + crash of thunder
Interval + light source enable/disable + colors
Obscured Lightning
Idle flashes hidden in cloud layer
Frequency
Both scale with the Thunder/Lightning value of current weather state.
Thunder sound settings live in the Sound Effects category — see below.
Manual lightning flash
UDW.FlashLightning(customLocation, customTargetLocation)
// customLocation: optional; should be at cloud level (root of bolt)
// customTargetLocation: if nonzero, the bolt ends there
Lightning striking specific actors
1. Add the UDW_Lightning Strikable Actor Interface to your actors
2. Implement "Test for Potential Lightning Strike":
outputs: can-be-struck-now (bool) + world location where strike hits
3. On UDW → Lightning category:
Enable "Enable Lightning Flashes Striking Actors"
4. Set "Fraction Of Lightning Flashes Which Can Strike Actors"
(how many potential flashes go to actors when any are in range)
5. Implement the interface's "Struck by Lightning" event
to spawn extra effects or run game logic
Lightning in Sequencer
1. Add UDW to the sequence
2. Create Event → Trigger track on UDW
3. Add a keyframe; right-click for properties
4. Endpoint → Quick Bind → Flash Lightning
5. Configure custom location/seed in keyframe properties
6. Check Call in Editor to preview in the sequence editor
Wind
Wind Direction
Controlled separately from weather state via Wind Direction in Basic Controls + the Wind Direction category. Direction drives weather particles and cloud movement on UDS.
Setting
Effect
Wind Direction Variation
Random noise variation at runtime, centered on Basic Controls Wind Direction
WOVs can override wind direction. If Apply Wind Direction is true on a WOV, the volume's wind direction wins as the player enters.
Wind Gusts
Wind intensity has a perlin-noise variation applied to simulate gusts. Settings in Wind Gusts: scale of variation, speed of the perlin noise.
Wind Debris
Small debris particles flying through the air when Wind Intensity is high. Category: Wind Debris.
Setting
Effect
Amount, scale, texture sheet
Debris appearance (texture must be 4×4 with alpha)
Wind Debris Particle Spawn Count
Live-updates at runtime
Spawning/collision
Uses Shared Particle Settings
Wind Directional Source
A Wind Directional Source is an engine component used by chaos cloth and SpeedTree assets. UDW makes and controls one with current wind by default.
Category
Setting
Effect
Wind Directional Source
Scale Wind Speed
How high Wind Speed is set on the source
Wind Directional Source
Disable when in interior
No wind speed when inside an interior
Wind Physics Force
Apply wind force to physics-simulating objects. Add the Wind Physics Force component as a child of any primitive component simulating physics. At runtime, the component queries UDW wind state and line-traces to test exposure.
Wind Camera Shake
Enable in Wind Camera Shake to shake the player camera at max wind speeds.
Setting
Effect
Scale of shake
Magnitude
Range of Wind Intensity that triggers shake
Threshold band
Player Occlusion masking(automatic)
No shake when player is in an interior. Controlled by Player Occlusion on UDS — see uds-modifiers-configs-state.
Weather Sound Effects
Enabled by default for wind, rain, thunder. Category: Sound Effects.
Setting
Effect
Enable/disable globally
Master toggle
Per-effect Volume
Scales with weather state and these settings
Close Thunder Delay Per KM
How much thunder is delayed from the visual flash. Raise for realistic speed-of-sound delay.
Runtime control
UDW.SetEnableWeatherSoundEffects(bool) // toggle all
// Or set the per-sound Volume variables directly
All UDW sounds use the UDS_Weather sound class. Add it as a child of your project's Sound Effects class so weather sounds inherit your sound mix.
Sound Occlusion
Default: a simple system periodically traces from the camera and adjusts sound volume + low-pass filter (muffling) if the player is in an enclosed space. Toggle/adjust in Sound Occlusion category.
The actual occlusion calculation lives in Player Occlusion on UDS — see uds-modifiers-configs-state.
Forced-occluded zones
Place a UDS Occlusion Volume actor (Blueprints/Occlusion/) to always-occlude a space. The Occlusion Sampling Mode in Player Occlusion decides if volumes are sampled.
Sound portals
UDS Occlusion Portal component. If instances exist around the occlusion sampling location, they're traced against and can negate occlusion when the trace is unobstructed. Use case: an open door/window letting outside weather sound naturally into the space.
Your own outdoor sounds following weather occlusion
Set your own sound sources to use the sound class UDS Outdoor Sound — they get occluded by the same volume attenuation as weather sounds.
Environment Sounds
System for general ambient outdoor audio (birds, insects, city ambience) that responds to time/weather and the sound occlusion. Sound Effects category on UDW selects the environment sound asset; a Forest ambience example ships.
Authoring an Environment Sound asset
1. Make a new data asset of type UDS_Environment_Sound
2. Point at a metasound source asset (the actual sound played)
3. Tune volume + parameter overrides
Metasound source format
For sound occlusion and four-direction stereo panning, output format must be 5.1:
Channel
Use
Front Left (0)
Directional audio from -X
Front Right (1)
Directional audio from +X
Front Center (2)
Directional audio from -Y
Low Frequency (3)
Directional audio from +Y
Side Left (4)
Global audio left channel
Side Right (5)
Global audio right channel
Directional audio is spatialized based on listener orientation and occluded directionally. Global audio is stereo, occluded by global occlusion.
Audio bus setup
Source Settings:
Enable Bus Sends: true
Enable Base Submix: false
+ Post-Effect Bus Send → audio bus "UDS_Weather_AudioBus"
Reacting to Time/Weather/Wind
Five input parameters UDW sets on your metasound:
Param
Type
Time, Weather, Wind
Integers
Weather Interp, Time Interp
Time parameters
Included metasound nodes use these:
Node
What it does
UDS_TimeWeather_VolumeManager
Outputs a changing volume using array inputs for what the volume should be in different times / weathers / wind levels
UDS_DayNight_VolumeManager
Simpler day/night version
Reference: included Forest Example metasound source at Sound/MetaSounds/.
Runtime control
UDW.ChangeEnvironmentSound(asset) // change at runtime
UDW.ChangeEnvironmentSound(null) // stop environment sounds
Gotchas
Splash particles only in one eye in VR — Splash Particles Rendering Mode = Translucent.
Particles not visible at all — invisible collision source blocking; or Show flags hiding sprites (Use Defaults); or Niagara compile fail (Full Rebuild on the asset).
Particles ignore an interior space (Simple Collision) — ceiling too tall; raise Ceiling Check Height. Or use Weather Particles Kill Sphere for a moving interior.
UDS Occlusion Volume doesn't block particles — Particle Collision Mode is Distance Field. Switch to Simple Collision (volume blocking is Simple-only).
Lightning never strikes the player despite the interface — Enable Lightning Flashes Striking Actors is off, or Fraction Of Lightning Flashes Which Can Strike Actors is 0.
Sounds go quiet at incorrect times — Sound Occlusion traces hitting surfaces they shouldn't. Adjust Player Occlusion on UDS (trace count, channel, update period).
No sound from open door/window — add a UDS Occlusion Portal component to the door/window. Make sure traces can reach it.
Wind doesn't affect chaos cloth / SpeedTree — Wind Directional Source category on UDW isn't enabled, or Disable when in interior is on and the actor is occluded.
Wind Camera Shake doesn't trigger — Wind Intensity below the threshold band, or player is occluded.
Environment Sound metasound playing but no panning/occlusion — output format isn't 5.1, or Post-Effect Bus Send to UDS_Weather_AudioBus is missing.
Custom outdoor sound not occluded with weather — assign it the UDS Outdoor Sound class.
