The H.Sie patch will give you a fog warning and reduce TC to 16 - as it will have your WO report the fog lifting again - even at periscope depth.
If you want to have a weather report with estimated visibility range, modify the en_menu.txt in (C:\GAMES\)Ubisoft\SilentHunterIII\data\Menu
Line 4100 reports the full visibility conditions - and should read something like "We have perfect visibility conditions, Herr Kaleun!"
Line 4101 reports ~ 70% visibility - and may read " resticted visibility, about 9000 meters."
Line 4102 is for ~ 40% visibility - so it may read "pretty hazy, Herr Kaleun! Visual range 5000 meters at best."
Line 4103 finally reports the fog conditions - "we're in heavy fog! Less than 1000 meters sight!"
(All data for 16 km atmosphere!)
The reports for clouds and percipitation are in the following lines - and you may be clever enough to formulate the lines accordingly, to encourage your WO in giving a propper weather report.
Modify line 4128 to look like this:
4128=Weather report: %s, %s, %s|Wind Speed %d meters per second, direction %3d.
(Maybe without kommata - depending on your formulations)
Your weather report could read like this:
Weather report: Partly cloudy and pretty hazy, Herr Kaleun! Visual range at 5000 meters at best! Wind Speed 6 meters per second, direction 260.
Weather report: Blue skies! A weather to father heroes! We have perfect visibility conditions, Herr Kaleun! Wind Speed 2 meters per second, direction 65.
Weather report: 80% overcast, Herr Kaleun! It's raining, restricted visibility, about 9000 meters. Wind Speed 10 meters per second, direction 145.
You can even fill in some neutral stuff like barometric pressure or "a storm has been reported further to the north" etc. - just add it to the visibility lines.
(I left the "NONE" for rain empty - I think it is a little bit stupid to report)
"No rain, no snow, no dead birds falling from the sky..."
Have fun!