Inspect the unexpected

Spent 4 nights at the Ninko Cabin in the Northern Whitefish Range

• On Monday 2/15, our party triggered a large avalanche at approximately 1:00pm. We were well aware the well documented persistent slab problem, and we believed the probelm to be less prevalent on southerly slopes, however, we found ourselves in a near-miss situation on a SE facing slope. (more details in the avalanche tab)
• Prior to our incident, we dug a pit on a SW facing slope at ~6100'. We found a very shallow snowpack with many facet/crust combos buried within. The upper snowpack was a pile of uncosolidated near-surface facets and some new snow leftover from the arctic intrusion.
• Stability tests pointed us to a troubling layer of facets 37cm below the surface and directly underneath a melt-freeze crust (likely the 1/13 layer). We conducted multiple test that produced collapsing with moderate force, but no propagation (ECTN22, PST32/100-SF)
• We decided to descend a South facing gully with slopes mostly 25-35 degrees in steepness. Our first rider was going to descend a short distance down a rib on the skiers right side of the gully, and wait there while the others in our group skied the more concave entrance near the center.
• While making their way down the rib, they skied breifly on the left hand convexity and triggered a persistant slab avalanche. The crown was ~200' and wrapped around the hingepoint of the rib. The slab failed on the same weak layer that we identified in our pit earlier. (facets on the underside on a melt-freeze crust).
• The rider was able to escape the avalanche by skiing hard to the right hand flank and avoided being carried into the gully. They were uninjured by the incident.
• The slide hit the gully and traveled a very long distance (~1000'), entraining low density uncosolidated snow and moving as a loose dry slough at middle elevations.
• We felt fortunate that no one was hurt and that this incident had happened to us early on in our trip, as we had plans for numerous descents in very similar terrain for the next couple days ahead. This Class A data would help us understand what types of terrain to avoid in the coming days.
• We spent the rest of the week skiing low angle (20-30 degree) terrain on north and south facing slopes and had quality riding and good stability. We periodically looked for test slopes to see if similar instabilities to mondays incident could be replicated, but never did find any obvious red flags. The take away for us was that we are starting to get less direct feeback and obvious signs of instability from our persistent slab problem, but we know first hand that dangerous conditions still exist and are producing life-threatening avalanches.
• I have attached a map that shows the approximate boudaries of the avalanche that we triggered. the "P" symbol on the same map shows where our snowpit data was compiled.