Bulletin d’avalanche

Mount Shasta

Mount Shasta Avalanche Center
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Danger d’avalanche

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

Points saillants

The mountains of south Siskiyou County have received three to five feet of snow over the past week. Today is the first full day of sunshine, which can impact avalanche danger. While signs of instability are decreasing and the snowpack is settling, hazards remain. Large cornices, wind slabs, and storm slabs still pose a risk, with the potential for human-triggered avalanches. Deep snow will continue to make travel difficult, and tree wells remain a serious danger. Stay vigilant and choose routes carefully.

Problèmes avalancheux

  • Loose Wet

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

    Despite cold temperatures today, anytime the sun comes out after fresh snow, this problem should be mentioned. Sun after fresh snow can cause instability. Lower-elevation sunlit slopes may see roller balls, pinwheels, and loose sloughs. If you observe the snow surface losing cohesion, switch to a shadier aspect. Watch for falling snow from trees—yesterday saw some bombs!

  • Storm Slabs

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

    Yesterday, skiers were still able to trigger small storm slabs on steep test slopes near treeline. Sun will aid settling, but may initially stiffen the snow into slabs. Storm slabs are most dangerous during and just after storms, but typically stabilize quickly here. Use small test slopes for assessments—they offer early warnings. Pay attention to what you see.

     

    Photo: Nick Meyers

    Storm slabs like this were still touchy to trigger yesterday 2.7.25 in near treeline terrain on a northwesterly aspect.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–3

    We’re uncertain about the size and sensitivity of wind slabs due to limited above-treeline observations. Wind-affected snow was seen yesterday, confirming wind loading. Over the past three days, winds from the SW, W, and NW have averaged 10 mph, gusting to 50 mph. Expect cornices and wind slabs on N, NE, E, SE, and S slopes. Approach slopes steeper than 35 degrees with caution.  

    Even without snowfall, avalanches can remain a risk. Wind efficiently redistributes snow, forming slabs in leeward areas. Watch for blowing snow and cracking—key signs of instability. To stay safe, stick to sheltered or wind-scoured terrain.

     

    Example of wind slab avalanche in above treeline terrain

Avalanche Discussion

In general, here are the ways sun can impact avalanche danger after fresh snowfall:

  1. Rapid Warming and Wet Avalanches – Strong sun exposure can warm the snow surface quickly, leading to melting and the formation of wet, heavy snow. This can increase the risk of wet loose avalanches or even wet slab avalanches, especially on sun-exposed slopes.
  2. Settlement and Stabilization – Solar radiation helps compact and bond the snowpack over time, reducing instability. However, this process depends on temperature fluctuations and the strength of underlying layers.
  3. Cornice and Wind Slab Weakening – Sun exposure can weaken large cornices and wind slabs, making them more prone to collapse or triggering avalanches on slopes below.
  4. Crust Formation – Repeated melting and refreezing cycles can create a sun crust on the snow surface, which may later act as a weak layer if buried under new snowfall.
  5. Aspect-Dependent Instability – Slopes facing the sun make them more prone to daytime instability, while shaded slopes remain colder and may maintain persistent weak layers.

Overall, sunny conditions can both stabilize and destabilize the snowpack depending on the timing, intensity, and prior conditions. Avalanche danger often increases in the afternoon as solar heating peaks. Watch out for those tree bombs today!

Deep snow, massive tree wells, and closed roads make backcountry access tough. Snowmobiling in deep powder is recommended for skilled pilots only. Trail breaking will still be tough for skiers. For easier access, Mt. Shasta Ski Park and nearby backcountry are great options, as are McBride Springs and the Nordic Center. Pilgrim Creek and Deer Mountain Sno-Parks remain open for motorized use—know your boundaries (click for map) if riding on Mount Shasta via FS31 road and power line access.  

The Everitt Memorial and Castle Lake roads are closed. Unknown opening. 

TODAY!! FREE, Snowmobile Specific, Avalanche Awareness and Beacon Clinic, 9am, Deer Mountain Snowmobile Park. Registration is not required. Bring a friend, the family, the kids and come hang out in the Deer Mountain warming hut for some coffee, donuts and avalanche education. Plenty of time will remain for a ride at your leisure. 

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