Observed:
The new rain effect in Arma 3 does not affect visibility other than the distraction of rain drops near to the player/camera.
Expected:
Heavy rain should reduce visibility. Distant objects should be obscured by an effect similar to fog. Ideally areas of rain should be visible from a distance, even when it is not raining on the player. {F23501} {F23502} {F23503}
Operation Flashpoint reduced visibility with rain, by using an effect similar to fog.
See attached screenshots (viewdistance 5000, same day and time for all shots).
full_rain.jpg - observed result with 100% overcast, 100% rain set in mission editor GUI.
full_sun.jpg - observed result with 0% overcast, 0% rain set in mission editor GUI.
full_rain-expected.jpg - an rough example expected result with 100% overcast, 100% rain set in mission editor GUI, using fog to reduce visibility.
Real life references:
very heavy rain, visibility severly reduced - https://www.youtube.com/watch?v=UHMaA38nU1Q
time lapse of heavy rain - http://footage.shutterstock.com/clip-2780089-stock-footage-amazing-unique-stormy-weather-time-lapse-featuring-sandstorm-lightning-strike-swirling-fast.html?src=rel/1503026:7/3p
time lapse of heavy rain - http://footage.shutterstock.com/clip-4537214-stock-footage-time-lapse-dark-turbulent-storm-clouds-sweep-across-arizona-desert-landscape-obliterating-a.html?src=rel/1503026:3/3p
time lapse of approaching rain against mountains - http://footage.shutterstock.com/clip-1503026-stock-footage-fast-time-lapse-rainstorm-clearing-over-the-santa-ynez-mountains-above-ojai-california.html
localised rain against mountains - http://www.mikeisaak.com/abraham-lake/image-5064639d7c542/
Here I used setFog depending on rain intensity http://www.youtube.com/watch?v=UfjMeFIhRV8
This issue is a feature regression rather than a feature request, since it was present in Operation Flashpoint, Arma, Arma 2 and the Arma 3 Alpha/Beta.
The new rain effect introduced in Arma 3 (maybe 1.05) removed the effect for the first time.