I have to say this has been a huge disappointment with my disc brakes. So many folks on these forums raved about their wet weather performance, yet for some reason I never got the impression that they squealed. Maybe I just missed it.
Yeah, mine squeal when wet or contaminated, which is a lot of the time in the winter. I heard organic pads helped but not really, not in my case anyway.
If you want silent wet weather performance roller brakes fit the bill but they don't have the stopping power of discs. They also drag quite a bit in cold weather. They're super easy to adjust though. If I lived in a wet but mild climate like the PNW they'd be hard to beat, at least for a rear brake.