A Skier entered the upper starting zone, and the Sensitivity of the Reactive Density Change in the New Storm Snow (1 to 2 inches above the New Snow/Old Snow Interface) allowed for propagation. This Storm Slab appeared to be at least 200 feet wide and it ran to the flats at the bottom of the runout zone. The debris piled up to at least 3 feet, and possibly 4 feet. The toe of the debris overran the public exit traverse. A quick hasty beacon search indicated that there was no one buried that was carrying a beacon; and the Tracks on the right Flank was the only apparent Rider evidence. The person that initiated the slide came into view out of the fog after we were observing the slide for approximately 5 minutes. The Starting Zone was at least 40 degrees, and it had a very slick/hard Old Snow Surface. It appeared that the long running length of this slide was enhanced by this Old Snow Surface.