Public Observation - Chain Lakes Avalanche: Northern Whitefish Range

2/22/2017The video shows a Wind Slab/Storm Slab triggered intentionally from the ridge onto a steep NE facing slope. The new snow on wind loaded terrain varied from 8 inches to 12 inches in thickness. We found it disturbingly easy to trigger this slab from the ridge onto a 35-40 degree slope. We were not finding signs of instability prior to triggering this avalanche. (no cracking, whumpfing, settlement of any kind in less steep and sheltered terrain below.We moved forward, but decided to back off our primary objective for the day. We opted for broken pitches (benchy terrain with smaller runouts) of generally less steep skiing that could be accessed from this same ridge. My partner skied first on a slope that varied from 20-30 degrees. The snow appeared stable and skied well. I descended second ~150ft further (from my partners tracks) across the slope where the angle varied from 20-35 degrees. Shortly after I passed the steepest part of this slope, it fractured and propagated ~30ft above me and ~60ft across on both sides of me. The slab was light and moved fast across a smooth faceted gliding surface. I turned to stop but was forced another 30ft downslope before resisting the pull. I let the snow move past me and down the slope. I was not buried or harmed, and skied the rest of the slope through the soft debris after the slide settled out ~150 feet below me.Luckily we had chosen to ski this lower consequence slope, where the slide quickly lost energy and did not result in any harm to myself or my partner below.  I had made a mistake in thinking it was okay to ski a short steep pitch, when we had seen dangerous signs of instability on a steep slope prior in our day. It was impossible to ski anything above 30 degrees safely in our area yesterday. At least on NE and E aspects near treeline.Lower in elevation on our decent back to the road, there were a few moments where we had to ski through short steep pitches again (significantly more sheltered, less open glades than above). We did so carefully, and did not trigger any slab failures. These were good test slopes that were definitely steep enough to slide. Although the new snow slab felt similar down low, I thought that perhaps the smooth gliding surface we observed higher up was less prevalent down low or in sheltered terrain.Learn from our mistake. This slab moved very suddenly and very fast on steep terrain, which could have been very dangerous in different terrain.