Anecdotally I've seen John Hicks hook up 5 times in a day with the water temp just at 38F... I myself have done well that low too, but those were on OP rivers with no pressure and midweek. In general for winter fish on the coast I'm more worried about the right flows and proper clarity rather than temps. Granted, I know solid scientific and anecdotal fishing evidence that temps affect the agressiveness of fish as temps near 50F, but in general we don't have control over it, so we just fish. I guess that's why we temper our expectations of a good day of fishing in the winter to be a solid hookup, and bringing multiple fish to hand in a day a spectacular outing. Finally I do remember a snowy day on the Sol Duc where we witnessed a steelhead slurping BWO's off the surface in some soft water. At first we though it was a sea run cut, but it eventually did a head to tail rise and we started throwing our gear at it in earnest. This was when I fished gear, so after a couple of casts, we ended up landing a nice wild fish around 9lbs.