Vancouver Island! Cold water, cold wind, and lots of blown out surf. Wing paradise in a 5mm wetsuit with hood, boots, and gloves.
Really though, it's maybe a break from the cold ... surf foiling has put me back in the water, after years out of it with longboarding, sup, sup foil, and kiting. But now with winging, I am out of the water enough that I've discovered it's doable with a 4mm, no hood, no booties or gloves. But that's on a sunny spring day.
Anyways, back to your point: San Fran is probably the west coast epicenter for cold water winging, with good wind and waves to play in, plus a dangerous kite launch. The Gorge will be bigger in summer, but it's not cold, least as far as I've read.