West Cabinet Mountains

On Sunday, a skier triggered a large, dangerous avalanche on an east-facing slope of Blue Mountain in the Southern Selkirks, and was fortunate to escape. Across all elevation bands, these dangerous slabs around three feet deep rest above a softer layer of snow that’s directly above a hard crust. Slab depth and the added contribution of stronger winds building deeper drifted slabs on leeward-facing slopes makes for touchy conditions and higher odds to trigger a potentially deadly avalanche. Stick to simple terrain and avoid traveling on, below, or adjacent to slopes steeper than 30 degrees while the storm snow settles and stabilizes.

Snow totals since March 12 range 27 to 33 inches in the Selkirk Mountains, 21 to 46 inches in the West Cabinet Mountains, and 16 to 20 inches in the Bitterroots and Silver Valley. These totals add up to two to five inches of Snow Water Equivalent (SWE) on top of a layer of lower density snow from March 9. All of which sits directly above a stout melt-freeze crust. This soft, weaker layer lurking above a hard planar interface is a prime setup to find trouble if you venture into the wrong terrain.

On Sunday, a solo skier triggered a large, dangerous avalanche on an east-facing slope of Blue Mountain just north of the Schweitzer ski area. We don’t have a ton of details, but a group nearby reports that the avalanche broke over 300 feet wide, around 2 feet deep, and traveled several hundred feet downhill. The skier was caught, not buried, and remarkably escaped. If venturing beyond the controlled confines of a ski area operation, please remember the sidecountry snowpack is a wild snowpack like the rest of the backcountry and does not benefit from skier compaction/ disruption - even where the snow surface is littered with prior tracks. This person was carrying avalanche rescue gear, but many people that venture into this zone do not carry the appropriate avalanche gear and that behavior is completely irresponsible.

Observations from this past week report the March 9 snow layer to be 4 to 6 inches thick in the West Cabinet Mountains and portions of the Bitterroot Mountains north of the Silver Valley. In other areas, this layer is only an inch or two thick. The varying thickness could influence overall sensitivity, so a good starting point to gauge conditions is to dig down and investigate. You may also notice the snow surface transition from soft to collapsible under your foot, and this is an indication that softer layers are close enough to impact with relative ease. The only ingredient in the recipe that’s missing is a steep enough slope.

Inverted slabs are often more reactive to human or machine triggering than “right-side-up” slabs where harder snow layers are below softer ones. A hard snow surface can provide a false sense of security or less immediate signs of instability, especially where the wind has pressed the dense snow in areas below ridges, cross-loaded gullies, and broader start zones. You may be able to descend further down a slope before being able to impact weaker layers below, and hard slabs can break in surprising ways around or above you, and travel long distances. The simple solution for today is to stick to lower-angled slopes free from overhead hazards or terrain traps below till these fresh slabs have a chance to mellow out.

As you migrate up and down elevations, you may also encounter other flavors of avalanche hazards such as loose dry or loose wet problems. The loose dry hazards are likely confined to steep, rocky, and wind-sheltered slopes, whereas wet concerns may be encountered around 4,000 feet where warmer air influence has made upper snowpack layers a bit more convoluted. Keep your head on a swivel and be ready to adjust your travels quickly if you experience rapidly changing conditions or see evidence of fresh avalanches in terrain you had planned to recreate. When stability is the question, terrain is always the number one answer.