Bulletin d’avalanche

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

New snow over a crust on southerly aspects and new snow over low density snow on northerly aspects will be your main concern today.  Winds picked up last night and will add to the storm snow problem today.  Watch for signs of instability within recent new snow, such as shooting cracks.  Be mindful of heightened avalanche conditions on 30 degree or steeper slopes, which was our concern yesterday.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Storm snow from overnight and yesterday, about 6-8 inches, has fallen on a variety of surfaces depending on aspect.  Southerly aspects have a sun crust from Sunday 3/12. Near Round Top in the Cabinets yesterday we found 3 inches of  new snow had not bonded well to the crust.  On northerly and shaded aspects, 3 inches of heavier storm snow from last night sits over drier lower density (less cohesive) snow.  We were seeing instablity in the unsettled low density snow due to the heavier snow loading on top.  Moderate to strong gusty SW winds have accompanied last nights storm, making loaded northerly ridgetop aspects possibly more reactive today. Wind or storm slab avalanches in the upper snowpack could trigger a step down avalanche to deeper weak layers of graupel 2-3 feet deep. Due to the variability in the pack make sure you are constantly checking stability by hammering on low consequence features or digging a pit when in doubt.

Avalanche Discussion

Our Monday tour took Kevin and I up Lightning creek into the Wellington drainage of the Cabinets. We found a couple inches of new snow had fallen overnight. The main part of the storm rolled in mid-day. Snowfall was wet and heavy while we toured on both sled and skis, taking stock of current conditions. We confirmed a 0.5 inch thick sun crust with moist snow under the crust on southerly aspects from Sunday. Shaded aspects held the same couple inches of wet overnight snow but sitting over drier softer snow. In both aspect driven cases the result is similar; the formation of storm slab over a weak interface is present. One interesting note on yesterday is Kevin and I performed one of the original, from the 1960s, snowpack tests called the Rutschblock. The test produced a failure 1 foot down after a few skier jumps (RB6). The Rutschblock is seldomly used, yet a great way to test the snowpack stability and observe how an isolated snowpack block reacts to human triggering.

The steady cycle of storms in the last couple weeks has deepened the snowpack; about 10 feet where we dug a pit on a north aspect. We were at the base of a steep north aspect that after checking the stability, we were not comfortable climbing up.  This was due to the failure in the strom snow from Friday and Saturday; it has not bonded enough for good stability and the heavier new snow will make the problem worse for today.  Several layers deeper in the pack popped out with moderate to hard force in our tests. These layers are trending towards gaining strength, but may be triggered in step down fashion.   An avalanche was observed in the Selkirks and shared by a recent submission on our Avalanche Obs page. Thank you for submitting observations, they are all helpful and especially so when sharing reports on avalanches or other signs of instability.

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