Bollettino valanghe

San Francisco Peaks / Kachina Peaks Wilderness

Kachina Peaks Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Careful snowpack evaluation and cautious routes will be essential for anyone venturing onto and below slopes greater than 30° steep. 

Triggering a wind slab avalanche will be probable on loaded leeward slopes and terrain features, on any aspect. Avoid cornices and convex pillows of wind-drifted snow. Northerly and northeasterly slopes near and above treeline may have conditions ripe for large to very large avalanches. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Cracking and collapsing wind slabs were observed on several aspects below treeline on Wednesday, February 15. Small cornices and large convex pillows were also observed. Avoid those when traveling in steep avalanche terrain. The wind slabs encountered Wednesday had a chalky and funky feel where harder snow overlaid softer snow. Wind slabs can also be very hard and may present a hollow drum-like sound as you traverse a slope.

    New slabs may have formed over near surface facets. Last weekend, various forms of near surface faceting were observed on all aspects, near and below treeline. 

    New wind slabs may be large enough to re-energize the dormant persistent weak layer of basal facets. Human-triggered wind slab avalanches may have enough force to step down, creating propagating failures in the weak layer of basal facets. If so, the avalanches may become very large. The basal facets and depth hoar have been documented on northerly and northeasterly slopes between 11,000' and 11,800'. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Some slabs that overlay the depth hoar/basal facets have gained significant strength and are pencil+ hard. It will be difficult to deform those slabs and collapse the faceted layers (creating an avalanche). Also, these faceted layers near the ground have strengthened over the last few weeks. Given these developments, it is unlikely that a person will directly trigger a persistent slab avalanche. However, human-triggered wind slab avalanches may have enough force to step down, creating propagating failures in the weak layer of basal facets, resulting in large to very large avalanches. 

Avalanche Discussion

We are about 24 hours out since the last snow accumulated, but winds moved snow most of the day yesterday and will continue to do so today. Cracking and collapsing wind slabs were observed on several aspects near and below treeline on Wednesday, February 15. Large drifts and small cornices were also observed. Overcast and obscure conditions prevented observations of many slopes near/above treeline. 

Cold temperatures will likely delay the bonding of new snow and wind slabs to the old snow surface. Pay close attention to the new/old snow interface for the next several days. 

Before the St. Valentine's Day Storm, some southerly slopes below 9500' were bare ground due to wind and melting. Previous winds had stripped some above treeline slopes down to rocks and cinders. 

The last known large avalanches occurred in mid-January during the MLK Storm Cycle. These large natural avalanches resulted from failures in the basal facets/depth hoar mentioned above. The last known avalanche occurred between January 23-27 and was a relatively small wind slab. 

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