Bulletin d’avalanche

Mount Shasta

Mount Shasta Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 8 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Dangerous avalanche conditions exist. Large human-triggered avalanches are likely in avalanche terrain. Observations have been nonexistent for days above treeline: you do not want to be the one to find instability in the alpine. Conservative decision-making is essential if you choose to travel on or below steep slopes. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    Several feet of new snow accumulated below, near, and above treeline since Thursday morning. Large human-triggered avalanches are likely. The likelihood of natural avalanches is decreasing as the new snow settles. However, there is plenty of snow available for transport, which, combined with moderate to strong northerly winds near and above treeline, will leave open the possibility of natural releases.

    Wind-loaded slopes are the most suspect, but unstable slabs may exist in sheltered terrain. Avalanches could release on density changes within the new snow, or on deeper layers in the snowpack. There remains some uncertainty regarding the sensitivity of these slabs, but a propagating test result yesterday indicates the potential for triggering exists. The winds shift to the north today after several days of southerly flow. This will challenge the assessment of wind-loaded terrain. Areas below ridgelines and cross-loaded gullies will hold the deepest slabs. 

    If you choose to enter avalanche terrain, use test slopes or smaller terrain features to assess the snowpack. Pay attention to red flags such as blowing snow, shooting cracks, and collapsing. Look for signs of previous wind-drifting, including cornices and pillow or lens-shaped snow. Consider the consequences before venturing onto or below steep terrain. Be especially careful if traveling on or below slopes steeper than 35 degrees.  

    There are plenty of opportunities for recreation in non-avalanche terrain on slopes below 30 degrees and not underneath steeper terrain. 

Avalanche Discussion

It has been quite a weather week in the forecast area. Here are some seven-day precipitation totals since December 20th at 4am:

  • Mount Shasta City: 9.85 inches of precipitation.  Since December 23rd at 4am: 8.16 inches.
  • Old Ski Bowl: 8.93 inches of snow water equivalent and 52 inches of snow (note: there is a data gap on 12/24). Since December 23rd at 4am: 51 inches of snow. 

For context, Mount Shasta City received about 23% of its average annual precipitation (~43 inches) in one week. In terms of avalanches, the first rounds of precipitation arrived warm and wet, plastering the upper mountain with rime ice. No avalanches were observed during a brief clearing on 12/24. The Christmas storm arrived much colder. Today will offer the first views of the upper mountain in days. 

Updated snow depths are uncertain on the west side of the forecast area, but most lower elevation access points are still building a snowpack that is usable for winter recreation. 

The Mount Shasta Ski Park opens today. Expect slippery roads if driving in the mountains. 

If you make it into the backcountry this weekend, please consider posting an ob! We'd love to hear from you. 

Régions couvertes