Have you seen the other weather tutorials out there? I have used them and the efects were not realistic. This tut will be on how to add rain, snow, and ash to your map and have it look and sound realistic.

First:

Select the material "particle/rain".

Second:

Place the brush in the area you want rain, or whatever.If you have an out door map make the brush cover the entire map. If you have level underground dont extend the brush to them or you will have it raining inside(DOH!).

Third:

Select the brush and turn it into a Func_Precipitation entity.

Fourth:

Choose what you want it to do. Ie: under the particle header select rain or snow or ash. Make sure you Apply it.

Fifth (if your using rain) :

Creat an ambient_generic entity. Find a sound for rain ionline or in the archive and apply it. Make sure under the flag tab you select play everywere.

Final Step:

If you selected rain make the bootom of the map have a thin layer of water on it by creating a brush with the water texture. If it is snowing or has ash falling try to have piles of built up snow or ash on corners and near walls. Compile your map and see what its like.

****IMPORTANT****
If you have made a dark map you might not have the best experience with this function. At times you can not see the rain if it is to dark.
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