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func_precipitation is a brush entity available in all Source games. It creates rain, snow, or ash inside its volume.

Rain Related Console Commands

There are a number of console commands that control precipitation rendering. See the Precipitation issues page for details on various issues and workarounds involving this entity.

Command Name Value Description
r_RainParticleDensity <Alien Swarm>[Portal 2] <float> Set the density to enable or disable any precipitation particle. Value 1 to enable and 0 to disable.
r_rainalpha <float> Adjusts transparency of rain particles.
r_rainProfile <bool> Displays stats on rain rendering costs.
r_RainHack <bool> Overrides density values set in Hammer. Enabling will result in longer and more dense rain than at 100%. Can help solve visibility issues.
Note:Rain may fall through brushes when this command is enabled.
r_rainspeed <float> Lower values will cause rain to disappear sooner and fall slower. Default value is 600.0f
r_RainSideVel <float> Controls sideways movement of the rain particles.
r_RainSimulate <bool> Toggles animation on the rain; freezes the rain when set to 0.
r_rainwidth <float> Widens the rain's alpha to desired value. Default value is 0.5
r_RainRadius <float> Distance from the brush where the rain starts/stops rendering.
r_rainlength <float> Changes the length of the rain particles. Default value is 0.1f
r_RainSplashPercentage <float> Percent chance of splash particles spawning when a particle is used.
r_raindensity <float> No function. Use r_RainParticleDensity instead.
r_rainalphapow <float> Raises the value of r_rainalpha exponentially.
Confirm:Some say this has no effect?

Warning: func_precipitations should not intersect with func_smokevolumes, as it can freeze the game. The exact cause of this is not clear.

Note:The precipitation created by this entity is not gpu-accelerated. In resource-intensive multiplayer games such as <Team Fortress 2>, it is recommended to use particle system to create weather effect rather than relying on this entity.


Density (0-100%) <integer>
This is the amount of particles that fall down from top side of brush. However distance from first particle to second depends on a brush volume size!
Color (R G B) <color255>
Color added to sprites which are rendered transparently (probably rain and snow particles)
Precipitation Type <choices>
Precipitation type
Value Name Description/Notes Example Map(s)
0 Rain Rain falling. CS:S map "de_aztec".
1 Snow Identical to Rain, use "Snowfall" instead.
2 Ash Ash falling. Appears with missing textures in most games other than EP1. A fix can be applied by extracting all 3 materials/effects/fleck_ash* textures and materials/effects/ember_swirling001 from ep1_pak_dir.vpk. Used throughout EP1.
3 Snowfall Snow falling. DoD:S map "dod_colmar".
4 Particle Rain (New with Left 4 Dead) Particle rain with slight mist and refraction. Left 4 Dead's "No Mercy" campaign, CS:GO map "de_aztec".
5 Particle Ash (New with Left 4 Dead) Particle ash with orange tint. Left 4 Dead's "Dead Air" campaign.
6 Particle Rain Storm (New with Left 4 Dead 2) Particle rain with denser, more angled particles. Left 4 Dead 2's "Hard Rain" and "The Passing" campaigns.
7 Particle Snow (New with Counter-Strike: Global Offensive) Particle snowfall. CS:GO map "ar_monastery".
8 Particle Bugs (New with Left 4 Dead 2) Particle flying bugs. Left 4 Dead 2's "Swamp Fever" campaign.
9 Particle Smoke (New with Left 4 Dead 2) Particle smoke with variable density. Left 4 Dead 2's "Dead Center" campaign.


Name (targetname) <string>
The targetname that other entities refer to this entity by.
Entity Scripts (vscripts) <scriptlist> (New with Left 4 Dead 2)
Space delimited list of VScript files (without file extension) that are executed after all entities have spawned. The scripts are all executed in the same script scope, later ones overwriting any identical variables and functions.
Script think function (thinkfunction) <string> (New with Left 4 Dead 2)
Name of a function in this entity's script which will be called automatically every 100 milliseconds (ten times a second) for the duration of the script. It can be used to create timers or to simulate autonomous behavior. The return value (if present) will set the time until the next call.
Note:Try to avoid expensive operations in this function, as it may cause performance problems.


Parent (parentname) <targetname>
Specifies a movement parent. An entity will maintain its initial offset from its parent. An attachment point can be added to the end of the name, separated by a comma.


Unlisted input. Changes the density of the rain, and may add additional particle effects like fog or leafs. It accepts inputs from -1 to 255.


Removes this entity and any entities parented to it from the world.
Functions the same as Kill, although this entity and any entities parented to it are killed on the same frame, being marginally faster than Kill.
AddOutput <string>
Evaluates a keyvalue/output on this entity. It can be potentially very dangerous, use with care.
Format: <key> <value>
Format: <output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
FireUser1 to FireUser4
Fire the OnUser outputs; see User Inputs and Outputs.
Use  !FGD
Same as a player invoking +use; may not do anything. Can also be invoked by creating an output that does not specify an input.
This input is not included in Valve's FGDs.
RunScriptFile <script> (New with Left 4 Dead 2)
Execute a VScript file from disk, without file extension. The script contents are merged with the script scope of the receiving entity.
RunScriptCode <string> (New with Left 4 Dead 2)
Execute a string of VScript source code in the scope of the entity receiving the input. String quotation may be needed when fired via console.
Bug: In <Left 4 Dead 2>, the code is executed in the script scope of the entity that fires the output, not the one receiving the input.
Warning: Never try to pass string parameters to a script function with this input. It will corrupt the VMF structure because of the nested quotation marks, which then must be removed manually with a text editor.
CallScriptFunction <string> (New with Left 4 Dead 2) !FGD
Execute a VScript function in the scope of the receiving entity.
SetLocalOrigin <coordinates> (New with Alien Swarm) !FGD
Send this entity to a spot in the map. If the entity is parented to something, it will be offset from the parent by this amount.
SetLocalAngles <angles> (New with Alien Swarm) !FGD
Set this entity's angles.


SetParent <string>
Move with this entity. See Entity Hierarchy (parenting).
SetParentAttachment <string>
Change this entity to attach to a specific attachment point on its parent. The entity will teleport so that the position of its root bone matches that of the attachment. Entities must be parented before being sent this input.
SetParentAttachmentMaintainOffset <string>
As above, but without teleporting. The entity retains its position relative to the attachment at the time of the input being received.
Removes this entity from the the movement hierarchy, leaving it free to move independently.



OnUser1 to OnUser4
These Outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.
OnKilled  (Only in the Left 4 Dead series)
This Output fires when the entity is killed and removed from the game.