How To Add Rain, And Snow, And Others to your Counterstrike Source Map.
Make a brush covered in "particle/rain" or "particle/snow" Under the block tool filter.
Place this brush in the area you want rain, or snow to fall.
Make sure the brush is at the top of your map.
Create the brush, and press alt+Enter to open "Object properties", look in the filter for "Func_Precipitation".
Step 5: Choose which particle you would like to use from the "Precipitation Type" at the bottom of the Object Properties. Either Rain or Snow, According to the latest news valve changed the precipitations to only rain and snow.
You can also change the color by going to the Color selection, and choosing a new color. Hit Apply when prompt.
Save You work, and test your map out. Enjoy your new Precipitation in your map.