Silver Valley & Bitterroot Mountains

Lawinenprobleme

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–2.5

  Persistent weak layers continue to drive lingering snowpack instability and are now buried roughly one to three feet below the surface. These weak layers consist of faceted grains associated with multiple rain crusts that formed during our first atmospheric river event in mid-December. Although recent days have produced fewer obvious signs of instability, this crust-facet structure remains widespread and capable of producing avalanches.

  Yesterday’s rain and modest but dense snowfall added additional weight to an already complex snowpack. This new load increases stress on the buried persistent weak layers, particularly where the overlying slab has become thicker and more cohesive. Even though these layers have been relatively quiet, incremental loading from new snow and rain may be enough to push isolated areas closer to their breaking point.

  Sensitivity is greatest where the snowpack is thinner and less insulated from recent cold temperatures. Shallow areas around rocky outcroppings, wind-scoured slopes, and mid-elevation terrain that received less snow and more rain remain the most likely places to encounter reactive conditions. The only reliable way to assess the structure and reactivity of the snowpack beneath you is to dig and investigate.

  Triggering these layers is more likely with larger loads, such as a snowmachine trenching deeply into the slab. Human-triggered avalanches remain possible, especially where a rider finds a thin or weak spot in the slab, or where warming temperatures have softened the upper snowpack enough to allow deeper penetration into the weak layers below.

  These persistent weak layers fall into a lower-likelihood, higher-consequence scenario. Expect little to no warning signs before an avalanche occurs. Mindful terrain selection and evaluation remain essential. Take extra caution around steep, complex terrain and carefully manage exposure to reduce the risk of an unexpected and potentially serious avalanche.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–1.5

  Temperatures have been above freezing for the past 24 hours in the majority of the Silver Valley-Bitterroots and will continue to be warm and above freezing on Saturday. This will make it possible to trigger a Wet Loose avalanche today. Although these avalanches will be relatively small, they have the potential to gain in size around mid-elevations where the snowpack is deeper, runouts are longer, and snow coverage is connecting more terrain features.

  Observing pinwheels that grow larger and stay intact as they move downhill or sinking to your boot top in wet snow are some of the first red flags that this problem is starting to take shape. Seeing snow shed around rocks and cliff bands that gain in size as it fans out and entrains more snow with it is an indicator that the Wet Loose problem is now well underway. 

  If these warning signs materialize, avoid crossing below cliff bands, in and around steep gullies, and be mindful of limiting exposure to steep overhead hazards to reduce risk.