Silver Valley & Bitterroot Mountains

Upper elevation slopes with wind-drifted slabs around a foot thick over a crust or weak snow layers are the most dangerous. Deeper drifts likely formed on leeward-facing slopes, in gullies, and will have a smooth, rounded appearance. Continue to make conservative terrain choices while the new snow settles, and retreat to lower-angled terrain away from ridgelines if you see cracking in the snow, see recent avalanches, or hear rumbling collapses.

The latest round of snowfall is slowly winding down. Winds may keep efficient drifting ongoing for a bit longer, but we expect this to be less widespread than previous days. Now that the brunt of storm is over, the new snow will get a chance to settle and may become less reactive to human or machine triggering. The main unknown at this point is how will the wetted, now buried Surface Hoar layer and faceted crust in the upper snowpack tolerate the new load, and how long before those concerns become stubborn or unreactive? This trend will likely be influenced by how deep Saturday’s rain percolated in the snowpack and whether the old, wet snow surface has locked up.

Since the primary weak layer(s) of concern exists in the top one to two feet of the snowpack we should anticipate rider-triggering remains an elevated potential till proven otherwise. Wetting drier faceted grains above a crust will help weaken their bonds and the water may pool on top of the crusts and disrupt that interface as it migrates downhill. Throw in additional weight of an overlying slab and we have the perfect stiff-over-soft combination near the surface. Cooler temperatures will likely help consolidate and stiffen near surface snowpack layers faster than those deeper, and this trend may require finding the shallow part of the slope to trigger an avalanche in buried weak snow layers.

Prior to the last storm, snowpack tests progressively required more force to initiate failures in these collapsible snow layers and buried crust as a function of the overlying slab becoming softer during last week’s High-pressure ridge. The old snow surface consisted of a pile of F to 4F hard facets, large Surface Hoar feathers, and crusted or wind-stiffened surfaces. An avalanche you trigger on a slope with freshly drifted slabs around a foot thick have the best odds to grow larger in size and be more dangerous. Use extra caution traveling on or below wind-loaded pockets on the backside of convex rolls and near slab margins.

You can use small, low-consequence slopes to evaluate the bond of the new snow and monitor how conditions change as you move up in elevation. Give an extra buffer traveling near slopes steeper than 30 degrees if you observe active wind-drifting or see signs of unstable snow. Sticking to lower-angle, wind-sheltered terrain will help reduce your avalanche risk.