Boletín de aludes

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Peligro de aludes

Thu
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 8 months ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Weak snow layers and crusts linger in the upper snowpack and continue to produce concerning, unstable results in snowpack tests. These weak layers are more reactive in areas with a thinner snow cover and in places where the winds recently deposited a stiffer overlying slab. Reduce your chance to trigger one of these large, dangerous avalanches by traveling on slopes less than about 35 degrees with deep uniform snow cover and free of rocky outcrops or steep rollovers.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–2.5

    Persistent weak layers responsible for lingering snowpack instabilities are now buried one to three feet deep in the snowpack. These weak layers consist of a worrisome array of weak faceted grains surrounding multiple rain crusts going back to our first atmospheric river event in mid-December. In recent days, these weak interfaces have been providing us with less and less feedback, but the same basic crust/facet structure remains widespread. Facet growth, and therefore sensitivity, are more pronounced in places where the layers are less insulated from the recent cold snap due to shallower over all snow depth. Places where the snowpack is shallower, whether that is around rocky outcroppings, wind scoured slopes, or mid-elevations that received smaller snow totals and more rain, are the most likely spots to encounter this problem. The only way to know for sure what the structure looks like below you or how reactive it may be is to dig down and investigate.Larger triggers like a machine trenching through the upper slab have a slightly higher potential to influence these weak layers than a human. Another scenario is a rider finding a shallow, not-so-sweet spot on the slope or where the overlying slab softens from the warmer weather making it easier to punch into deeper weak layers. The current state of these persistent weak layers has migrated to a lower likelihood, higher consequence regime. This means you are not likely to receive any warning signs before an avalanche occurs. Continue to make more mindful terrain choices and avoid traveling in steeper, more complex terrain to avoid an unexpected avalanche encounter.

    (12/30/2025)

    Pit tests show propogation potential still exists in weak facet/crust combo layers from December. This one from 6,000ft on NE aspect near Burke Summit failed (ECTP22) in the weak facets between older consolidated snowpack and a thick crust from one of the early December atmospheric river events. An avalanche on this layer would be a low probobility, high consequence event.

    Photo: Mikey Church

Avalanche Discussion

Storm totals since December 26 range one to two feet across all forecast zones, and some higher elevation areas likely received closer to three feet of snow. Temperatures finally behaved for once and progressively lowered during the storm as precipitation engulfed the region. While this has made for improved surface conditions, it overlays a complex snowpack going back to our atmospheric river events from mid-December. The recent cold snap interacted with a warm wet snowpack to promote rapid faceting around crusts. The reactivity of these layers varies greatly between our forecast zones and even within the same geographic areas. Facet growth is less advanced in locations where deeper snow has insulated the problematic layers, such as in the East Cabinets and the far north end of the Selkirk zone. Facet growth is most pronounced in areas where the snowpack is the shallowest. At this point we are seeing less and less feedback from these problematic weak layers, and less consistency across the forecast areas, but the same basic structure needed to produce a large destructive slab avalanche is widespread.

 We now have to manage the inherent uncertainty of the Persistent Weak Layer problem. Today you might get away with a lot without encountering any red flags, but if you are able to trigger a deeper failure, those slides will be much larger, more difficult to escape, and potentially deadly. A conundrum is that the most stable snowpack will be where the weak layers are buried the deepest and are most insulated but also have the largest overlying slab. You can manage this problem by avoiding the most complex terrain and spend time digging into the snow to understand what is beneath your feet on your chosen slope. Stick to slopes that are more uniform and don’t have rocky outcroppings or other likely trigger points.

 Yesterday we saw sluffing and roller balls coming off cliffs on solar aspects. But with a cold overnight refreeze and temperatures forecast not exceeding mid 30’s we believe wet snow problems will be isolated and unlikely today. However, the return of sunny skies today means surface wetting is a possibility, especially around cliffs on steep solar aspects, SE-S-SW. Take pinwheels that grow in size and deep boot penetration as fair warning that wet loose problems are likely to follow.

 With the pleasant weather and great surface snow it’s tempting to step out today. Don’t let a bluebird powder day lure you into a potentially dangerous situation. Today you might get away with a lot, but hitting the wrong spot could provoke a large dangerous slab avalanche. Our purpose here is not to frighten people into not recreating, but rather give you the information needed to make sound decisions in the mountains. Choose simple terrain where the snowpack is deeper and more uniform. Practice good safe travel habits, like one person on an avalancheable slope at a time, mind alpha angles and keep eyes on your partner from a safe spot. The winter season is still young and plenty of days are ahead for fun backcountry recreation.

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