Boletín de aludes

Selkirk Mountains

Idaho Panhandle Avalanche Center
Ver en el mapa

Peligro de aludes

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

Lo esencial

Mid and upper elevation slopes with wind-drifted slabs around 8 inches thick above a slippery crust are the most problematic. Use caution traveling on slopes around 35 degrees below ridgelines, in gullies, and on the backsides of convex rolls where drifts will likely be deeper. Shooting cracks and audible collapses are signs of unstable snow and suggest moving to lower-angled terrain or areas sheltered from the wind.

Problemas de aludes

  • Persistent Slabs

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

    Weak, faceted grains are sandwiched between two rain crust in the upper snowpack. The hardness and thickness of the upper rain crust varies across our forecast zones and has been found up to about 6,500 feet. Where the crust is around 2 inches thick or more, weak grains have been reluctant to fail in snowpack tests. Places where the crust is thinner and breakable, tests continue to produce failures with moderate to hard force. Your odds to trigger a deeper, more dangerous avalanche may increase as you move higher in elevation where the overlying crust is less supportive or non-existent.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    On Tuesday, riders near Lone Lake in the Bitterroot Mountains triggered an avalanche from a steep, rocky portion of the slope where winds drifted recent snowfall into a more cohesive slab above a rain crust.  Ongoing moderate westerly winds around 6,000 feet and higher continue to form broader drifts on leeward-facing slopes and these slabs will remain reactive during their formation. Triggering an avalanche from a drifted area can break wider than you expect and may provoke a deeper snowpack failure. Pay attention to how snow depths change as you move up in elevation and avoid traveling on slopes around 35 degrees where the snow surface looks smooth and rounded.

Avalanche Discussion

Natural or human-triggered slides are bulls-eye evidence of unstable snow. Since snowfall ended last Sunday, field observations have reported generally good bonding of the new snow to the newest crust that formed after light to moderate rain on December 7. Since then, pesky winds have continued to transport snow onto leeward slopes and terrain features, and this has helped stiffen the snow surface. Despite field observations reporting mixed results in snowpack tests above the crust, Tuesday’s rider triggered slide confirms that steeper slopes harboring a cohesive slab of snow over a slippery sliding surface are where you can find trouble.

As you move up in elevation, pay attention to how snow depths increase and whether the surface slab gets stiffer. Use small non-consequential tests slopes to look for cracking and collapsing and dig down to see how the new snow has bonded to the buried rain crust. Be wary of terrain below ridgelines where you observe active wind-loading or if you don’t feel the rain crust below you. Keep in mind that triggering an avalanche near the surface without a thick, stout crust below has a better chance to provoke a deeper failure in weak facets around 2 feet deep.

At mid and lower elevations, rainfall amounts last weekend were much higher. In its wake, a stout, knife hard crust around 2 inches thick exists across all aspects. On those slopes, the forecast staff reports fewer concerning failures in faceted grains above the November 23 rain crust, and those layers are slowly getting harder. The rain did a fairly good job of knocking down most of the larger Surface Hoar grains that grew during last week’s cool, dry period. However, the forecast staff has dug a few snowpits where these concerning grains are refrozen and upright. This setup is easier to identify where the crust is thinner.

At higher elevations, generally above 6,500 feet, the crust gets thinner and eventually becomes non-existent. In the Selkirk Mountains, the December 7 rain crust is significantly thinner, and the same faceted grains below are softer and more worrisome than in the West Cabinet and Bitterroot Mountains. While triggering a larger, more dangerous avalanche is less likely than triggering a shallow slide near the surface, anytime we have weak snow grains near the surface, traveling with an investigative mindset will help reduce your avalanche risk.

---

As our snowpack continues to evolve, please take a moment to inspect your avalanche rescue gear – beacon, shovel, and probe. Its also a good time to refresh on your snow and avalanche training and consider showing up to one of our Avalanche Awareness talks. The next one is December 11 at Solnix in Spokane at 6 pm.

Regiones cubiertas