Bollettino valanghe

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

A variety of weak snow grains that developed at the end of January are now buried several feet deep by a cohesive slab of snow. The potential remains to trigger a large and deadly avalanche on these weak layers, albeit a bit more difficult due to a stiffening overlying slab. Diligent terrain management of sticking to slopes around 30 degrees and not traveling directly underneath steeper slopes or convexities is the best way to manage the current hazard. Adjust your travels if you hear rumbling collapses, cracking in the snow, or see recent avalanches on similar aspects to where you had planned to recreate.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2

    An assortment of weak grains currently buried two to three feet deep are the perpetrators of the weak upper snowpack structure. Slopes near tree line and down to about 5,000 feet continue to be the most reactive. Fragile surface hoar grains are found primarily north and east-facing aspects. On sunnier aspects, facets above the crust are growing larger under the influence of cold temperatures, and the larger grains below are slow to heal. Even if you don't find surface hoar or a faceted crust below, places with a good helping of near-surface facets are also producing worrisome results of unstable conditions. Although the flavor of weak grains vary across aspects, these have all shown to be a problem. Due to slab depth above these persistent grains, triggering an avalanche would result in a large, potentially deadly slide.

    Although all of the forecast zones have a similar set up of avalanche problem and aspect distribution, the depth of the slab on top adds variation to the potential size of avalanche you can trigger. The Selkirks and West Cabinet Mountains received higher snowfall totals from the last storm, which has resulted in a thicker slab. The Silver Valley-Bitterroot Mountains received lesser snowfall, resulting in a slightly smaller avalanche in comparison. 

    Photo: Izzy Davis

Avalanche Discussion

Recent observations across all forecast zones continue to support the sensitive nature of the snowpack. Recently observed natural avalanches and propagation in snow pit tests with easy to moderate force all support the message that the snowpack is still fragile and triggering an avalanche remains a possibility. Conditions after the last round of snow hasn’t allowed the snowpack to heal, and sustained cold temperatures have furthered the extent of faceting- creating an environment where the weak grains are resistant to bond to one another.

 All of this is setting the stage for a weak snowpack to persist for a long period of time. These stubborn weak grains are not expected to go away anytime soon and are acting like a sleeping dragon in the snowpack. Once natural avalanche sightings start to decrease and propagation becomes less frequent in snowpack tests, the set up for a weak and dangerous snowpack will continue to persistent long after.

Cautious terrain management and avoidance are the best tools to avoid running into trouble. Recreating on slopes less than 30 degrees and avoiding overhead hazards are best practices until the snowpack has the ability to heal.

While making travel plans for the day, consider the complication of another round of arctic air influencing the area. Such harsh and cold conditions can turn a minor setback in the backountry into a very big problem. Having a solid plan and sticking to it, as well as good communication are all strategies that will help set you up for success. 

 

**We continue to receive intermittent reports of opening glide cracks and some failing naturally producing large to very large glide avalanches. Avoid traveling on or below slopes where a glide crack has opened. These types of avalanches are difficult to forecast when they will release.**

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