Silver Valley & Bitterroot Mountains

Dangerous slabs of snow one to two feet deep exist at mid and upper elevations. These slabs rest above a softer layer of snow that’s directly above a hard crust. Slab depth and the added contribution of stronger winds forming deeper drifted slabs on leeward-facing slopes will increase your chance to trigger a large avalanche. Avoid traveling on slopes steeper than 30 degrees and stay clear of lower-angled  slopes with steep hazards directly above.

Snow totals since March 12 range 20 to 26 inches in the Selkirk Mountains, 16 to 36 inches in the West Cabinet Mountains, and 10 to 14 inches in the Bitterroots and Silver Valley. These totals add up to one to three 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.

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.