We were skiing a generally benign east/northeast facing slope which had received lots of windloading over the last 24 hours. The snow was fairly chalky and skied like stiff pow, but it was actually a firm soft slab. The slide was slow moving and I didn't realize I had even triggered anything until I had finished the pitch and looked back. It ran on about a 32-35 degree slope and went about 300 linear feet. Probably a class 1+.