I've been successful with my recent patrols attacking in heavy fog. I position my sub abeam of the target at about 350m, and when it shows up, just let loose. Sometimes, though, I've had to get a little bit closer because I can't get a visual. As soon as I do, I hit reverse flank and wait until the distance that the torpedo can detonate.

Hopefully, it keeps working for me. :ping:

I also find using the observation scope rather than the attack scope in bad weather increases the distance at which I can lock onto a target. since the weather is bad the chances of them spotting the bigger scope aren't good anyway so it is a good tradeoff. I find you can close to within medium range on the hydrophones in bad weather, pop the obs scope up till you can visually acquire the target to refine your bearing to shoot.

Usually I just do basic trim dive early in the morning. In bad wather it's the same but having just a longer period submerged (usually about 2 hours) and I also dive deeper (60 meters vs 40 m).