Bulletin d’avalanche

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Danger d’avalanche

Mon
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

The likelihood of triggering an avalanche has continued to decrease; however, it is still possible, particularly in terrain at and above treeline. The highest likelihood is in areas where recent wind pockets have formed. Additionally, there is continued potential for triggering larger persistent slab avalanches, particularly in regions with shallower snowpacks.

Exercise heightened awareness and prudent decision-making while navigating slopes at and above treeline. Travelers should avoid steep slopes, pockets of wind-loaded terrain near ridgelines, and areas of widespread wind deposition, such as cross-loaded gullies and starting zones. 

Problèmes avalancheux

  • Wind Slabs

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

    Winds near treeline have occurred at moderate levels, while ridgetop gusts have been stronger.  There has been widespread snow transportation at and above treeline on several aspects. For example, on the east face of Agassiz, snow has been loaded on the northeast aspect from south-southwest winds and on the south aspect from recent north winds (See photo of Agassiz Peak below). Avoid loaded starting zones, wind drifts, mounds of snow, pillowed areas, and cornices.  If large enough, a wind slab avalanche could step down to a persistent weak layer and release a large to very large persistent slab avalanche.

    A large (D2) natural avalanche released on a northwest aspect in the Upper Bowl while it was closed, likely during the last pulse of moisture (2/8/24) (See Photo). The starting zone for this avalanche was heavily wind-loaded due to south-southwest winds during the storm. This avalanche was large enough to injure, bury or kill a person.

    Natural large (D2) avalanche on a northwest aspect loaded by south-southwest winds in the Upper Bowl while it was closed.

    Photo: Tanner Porter

  • Persistent Slabs

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

    In areas that possessed a snowpack prior to the arrival of our last storm, two primary persistent weak layers have been buried deep below the surface. The highest in the snowpack is a single or set of small (~2cm) melt-freeze crusts that developed during January and are surrounded by facets and near-surface facets. The second persistent weak layer is at the base of the snowpack, where the early December snow has faceted, creating a layer of basal facets and depth hoar. These layers continue to be a concern; however, on many slopes, they are buried deep enough that they would likely not be triggered by a traveler's weight. The highest risk of initiating an avalanche in one of these layers is in areas with shallower snowpacks (<2m) where a traveler's weight could cause propagation. Additionally, if a wind slab avalanche was triggered, it could step down to these persistent weak layers. Although unlikely, if triggered, expect the avalanche to propagate in surprising and unpredictable ways with a possible crown height of 4'-7', making this problem especially difficult to manage.

    The best way to manage the risk from persistent slab avalanches is to make conservative terrain choices. Persistent slabs can be potentially triggered by a skier’s/boarder’s weight, even weeks after the last storm.

    (2/4/2024)

    Snowpit displaying reactivity at persistent weak layers prior to the recent storm.

Avalanche Discussion

Storm totals during the week ranged between 40-60" of snow.  Over 5" of SWE has been recorded at the Snowslide Canyon  Snotel site since the storm's beginning. On  Friday, a short window of visibility was available and revealed debris from numerous natural avalanches that were released during the storm. The first was likely a wind slab avalanche, occurring on a northwest aspect in the Upper Bowl, while it was closed, likely during Thursday's (2/8/24) storm. In addition to this avalanche, several older debris piles were noted within the Humphreys Cirque on east and southeast aspects. Due to significant weathering, it was challenging to estimate when, during the storm, these released and the size of these avalanches.

As mentioned previously, two primary persistent weak layers are the focus of concern. The first is a set of persistent weak layers, facets, and near-surface facets located above and below various melt-free crusts.  The continuity of these layers has been hard to assess, but if present continuously in the snowpack, these layers could also result in large avalanches. The second of these layers is a set of basal facets and depth hoar buried at the bottom of the snowpack. This layer has been found most commonly across many aspects.  Its presence seems widespread except in some south-facing areas where snow has melted off between storms and other high-terrain areas where snow has been significantly stripped by wind. 

Assessments on Friday (2/9/24) and Saturday (2/10/24) showed the wind slab to be reactive in extremely isolated pockets, with the majority of the wind slab being stubborn to non-reactive. Additionally, over the last few days, ECTP21-24s have been reported to fail on the depth hoar at the bottom of shallower snowpacks on various aspects.

Winds have been variable and intermittent during different phases of the storm. At upper elevations, snow depths are highly variable, with some aspects and slopes completely stripped, while other areas have become loaded by wind. Use appropriate spacing when traveling and avoid wind drifted locations.  Retreat or find a different route if cracking or shearing is observed.  

Note that the snowpack depth and layers were quite variable pre-storm.   For those seeking more information, please view the observations page.  https://kachinapeaks.org/Observations/#/view/observations.   You can also check out the snowpits published this week at snowpilot.org.

Régions couvertes