Bulletin d’avalanche

Mount Shasta

Mount Shasta 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 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Unstable snow exists in terrain near and above treeline, where southerly winds have developed wind slabs. Look for these instabilities on W-NW-N-NE aspects where slopes could fail a foot deep, take you off your feet, and potentially bury you. At upper elevations (10,000+ ft), there is potential for some larger lurking slabs. If the sun makes an appearance today, there could be a short-lived wet-loose instability on solar aspects. Evaluate terrain cautiously before committing to a steep line. 

Problèmes avalancheux

  • Wind Slabs

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

    The past 24 hours have provided a reinforcing 3–4 inches of snow, on top of the 10 inches that had fallen the night before. This puts storm totals at around 13–14 inches at treeline. For the most part, this snow is relatively dense, limiting its ability for wind transport. Nonetheless, winds blew moderately out of the south, and wind loading is still likely around exposed slopes, and ridgelines. Look for wind loaded slopes on W-NW-N-NE aspects, primarily in terrain near above treeline. Today, winds will shift to the northwest, potentially beginning to load SE-S aspects. This is not expected to be significant through the day, but things can change. Keep your eye out for shooting cracks, failing test slopes, and hollow sounding snow drifts. If in doubt, avoid avalanche terrain on leeward aspects around ridge tops and exposed slopes.

    Visual depiction of wind loading and cross-loading dynamics

    Photo: Illustration from Allen & Mike’s Avalanche Book by Allen O’Bannon and Mike Clelland (Falcon Guides).

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    This problem is a precautionary listing for today's expected weather. This time of year, our snowpack is susceptible to quick changes in moisture with even the shortest periods of sunlight. With the already warm and dense surface snow, it won't take much for destabilization to happen. As the day progresses, monitor surface snow conditions with quick hand pits, attempting to make snowballs, or cutting test slopes. If the surface snow begins to feel sticky, clumpy, or “upside down” (where heavy snow is on top of light snow), it's about time to exit avalanche terrain. This will happen first on south and west aspects, where the sun has the greatest influence.

    Small entrainment of wet loose snow. An indicator of rising surface instability. 

Avalanche Discussion

The low pressure system from the last 2 days is expected to push out this morning, transitioning the forecast area to a dry, northwest to southeast flow. Total storm accumulation (since 3/22) is ~13-15 inches at treeline on Mount Shasta, with less in our terrain to the west. As expected, the system initially came in warm, and wet, cooling as it progressed. This has provided a “right side up” snow structure, and some observed storm slab instability within the new snow. It's late March, and the new snow is consolidating quick. This means the storm slab instability has largely settled out, and the primary concern is now wind slab development.Yesterday's observations were from the Gray Butte area, where little was seen in terms of wind slab. Occasional small slabs were triggered with skis on northerly aspects, however, these were never larger than a few square feet. That being said, at upper elevations (10,000+ ft), there could be some larger wind slabs looming. As the dominant wind begins to shift to the northwest, expect wind transported snow to accumulate on SE-S aspects. Today will be the early stages of this, but something to keep on the radar.There is a chance, in the late afternoon, that the sun will make an appearance. This time of year, the sun has a strong effect on the surface snow. If the sun comes out, expect a rapid rise in wet loose instability. This time frame will likely be quite short before cooling in the evening, but this is another precursor for the days to come.

Régions couvertes