I made a little weather report mod for myself some years ago. You have to modify the en_menu.txt or de_menu.txt.
...\Ubisoft\SilentHunterIII\data\Menu\de_menu.txt
in German it looks like this:
4100=wir haben ausgezeichnete Sicht Herr Kaleun. Der Luftdruck fällt leicht.
4101=mittlere Sicht, weniger als 6000 Meter. Es wird weiter abkühlen.
4102=Sicht nur etwa 3000 Meter, sehr diesig. Vermutlich wird Nebel aufziehen.
4103=dichter Nebel, Sicht unter 500 Meter. Nördlich wurde eine Sturmfront gemeldet.
4110=wolkenloser Himmel,
4111=der Himmel ist bewölkt,
4112=dichte Wolkendecke,
4120=
4121=es regnet -
4122=starker Regen, Herr Kaleun -
4128=Wetterbericht: %s %s %s|Wind mit %d Meter pro Sekunde aus Richtung %3d.
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A rough translation:
4100=perfect sight conditions, Herr Kaleun. Barometric pressure is slightly falling.
4101=medium sight, visibility only 6000 meters. It seems to cool down.
4102=sight conditions only 3000 meters, very hazy. Probably we'll get fog.
4103=heavy fog, sight less than 500 meters. Northwards a stormfront was reported.
4110=cloudless sky,
4111=the sky is overcast,
4112=heavy cloud cover,
4120=
4121=it's raining -
4122=heavy rain, Herr Kaleun -
4128=Weather report: %s %s %s|Wind %d meters per second from %3d.
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4120 was 'no precipitation' - I thought it to be stupid.
You can insert something else - maybe temperature.
There are no real temperature variables ingame.
Distances are for original 8 km horizon.
4128 should not be changed.
Make yourself some better translation (heavy, heavy and heavy), the German version is quite good.
You can copy/replace the complete block into your menu.txt.
Try youself and have fun.