Bountiful Ridge - Sessions West Cloudy, mid to high 20's, no wind. Hard slab, Northwest aspect, 8400 feet, 38 degrees, 15 inches deep, 100 feet wide, movement on burried surface hoar. On second run, a slab partially released by a ski cut while dropping off a ridge. The slab moved 4-6 inches, compressing and folding along bottom edge, 75 feet below the crown. There were no indications of instability. No cracking or collapsing. First run (same slope) did not produce any indicators of instability. There were no indicators of wind loading. No pillows or hollow sounding drifts. The conditions were great skiing. 6-8 inches of medium density powder, atop 5 inches heavy snow. Seemed very stable and I didn't hesitate to ski the line. Very disturbing to see it crack on my second run. The UAC forecast was spot on by saying conditions are tricky and "don't be too comfortable" even when indicators say "go".