Bulletin d’avalanche

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Danger d’avalanche

Sat
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Avalanche problems are complex and widespread at upper elevations and mid-elevation ridges today. Reactive wind slabs are possible on all aspects at upper and mid elevations today. New/old snow interface and multiple buried weak layers should be investigated thoroughly before committing to avalanche terrain. Extreme cold temperatures mean any mishap or delay will automatically become a more dangerous event, so build a wide safety margin into your plans if you venture into the hills today.

***Yesterday, there was a fatal avalanche accident near Stevens Peak in the Silver Valley. Rescue and recovery are continuing today. For more information you can find a report on the IPAC home page or Shoshone County Sheriffs FB page https://www.facebook.com/p/Shoshone-County-Sheriffs-Office-100064700947434/

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1.5–3

    Avalanche problems are complex and widespread at upper elevations and mid-elevation ridges today. Reactive wind slabs are possible on all aspects at upper and mid elevations today. New/old snow interface and multiple buried weak layers should be investigated thoroughly before committing to avalanche terrain. Extreme cold temperatures mean any mishap or delay will automatically become a more dangerous event, so build a wide safety margin into your plans if you venture into the hills today.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    A layer of surface hoar that was formed on New Years Day was buried intact by the most recent storm cycle.  This buried surface hoar was preserved on less sun affected slopes and can be found intact on north facing aspects. We have also found a weak layer of facets above the December 20th rain crust. Deeper in the snowpack, the late November surface hoar is harder to find and less reactive in isolated areas on north facing slopes, but we are not ruling it out until we can confidently say that it is no longer a threat. With the new snow load, these persistent weak layers have the potential to become activated. We should treat them with respect until we find evidence that they are no longer a problem. 

Avalanche Discussion

There has been a report of an avalanche incident yesterday near Stevens Peak. We are aware of the incident and an investigation will take place as soon as possible.

Yesterday, George, Izzy and I toured up the Jammer/Boom Truck Route to West Willow Peak. We stuck to safe terrain as heavy snowfall and howling winds hounded us throughout the day. We heard several loud whoomphs and recorded propagation on a layer of stellar dendrites and graupel within the recent storm snow in one of our pit locations.

Abundant new snow over the past week has doubled the depth of our snowpack in many places, with upwards of 30” being reported from Silver Mountain’s snow study plot. In general, the new snow came in “right-side-up”, meaning falling temperatures throughout the storm helped deposit progressively lighter density snow: cold low-density powder fell on top of heavier snow.

However, drastic changes in weather are always a red flag for avalanche danger to rise. In our case the new snow load has added stress to the weak layers within the snowpack while strong winds have transported and packed snow into cohesive slabs. These issues are especially acute in the upper and mid elevation bands where new snow accumulation and winds have been greatest. Navigating these complex avalanche hazards safely is a real challenge that takes careful assessment and sound decision making. Even seasoned professionals are taking a step back to allow time for things to calm down. Superb skiing and riding conditions can be found on low angle slopes (less than 30°) and sheltered terrain that are not threatened from above by avalanche hazards.

The arctic cold front that entered our region last night is forecast to bring near record breaking lows and will not ease off until early next week. National Weather Service has mentioned wind chills that could reach -45°! Bear this in mind if you venture into the backcountry this weekend as even a minor misstep could become a much more serious problem when faced with the extreme cold. Add a margin of safety into plans, please.

Régions couvertes