Avalanche forecast

Mount Shasta

Mount Shasta Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The avalanche danger is CONSIDERABLE above treeline and MODERATE near treeline where there was a previously existing snowpack.  Areas below treeline did not have a substantial snowpack prior to this storm and need more snow to harbor avalanche potential.  Avalanche danger will increase as more snow accumulates.  Assess how well the new snow is bonding to the old snow surface.  Even a small avalanche could take you for a rough ride due to low snow-cover and exposed objects.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Wind from the S-SW-WSW will redistribute new snow and load NW/N/NE/E/SE facing slopes. Areas of deeper snow on the downwind side of ridges should be suspect.  Wind slabs are the release of a cohesive slab of snow formed by the wind. Wind transports snow from the upwind side of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and can sound hollow, and can range from soft to hard. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Storm slab avalanches are the release of a cohesive layer (slab) of new snow that breaks within new snow or on the old snow surface.  Mid-storm temperature fluctuations produce variability in storm-snow density that can contribute to instability.  Near tree line there is probably not enough new snow yet to pose a hazard, but with heavy snow forecasted throughout the day and night, this could change.  Assess how the new snow is bonding to the old snow surface, and be skeptical of "upside down" snowpack structures where low density snow is overlayed by heavier, denser snow.  

Avalanche Discussion

The Mt. Shasta region received its first substantial snowfall in late October and early November from a series of atmospheric rivers that deposited several feet of snow on the mountain.  November and early December were drier and warmer than average, and most of the snowpack near and below treeline melted back to bare ground.  A few days of below- freezing temperatures preceded the current storm, and surface conditions became firm and icy.  Some isolated weaker snow (facets near crusts) also developed on shady, northerly facing aspects near and above treeline.  Most areas in the forecast zone besides Mt. Shasta (Castle Lake, Mt. Eddy) did not have significant (or any) snow on the ground prior to this storm.  However, Ash Creek Butte weather station has been reporting around a foot of snow since those early season storms, but there have been no field observations to corroborate this.  Expect the snowpack in those east-side locations to potentially harbor some weak snow (facets).  As we move further into this winter storm, it will be important to assess how well the new snow is bonding to the old snow surface.  

Join us at 9 a.m. Sunday, December 12th for our Companion Rescue training. These are all free, and you do not need to sign up, just show up! Donations gladly accepted. Since the gate is closed this weekend up to Bunny Flat, we will instead be holding this clinic next to the baseball field above Sisson Middle School in Mt. Shasta City, near the cross streets of Rockfellow and Lake Street. Next weekend, don't miss out on our Community Movie Night.

A reminder that the Siskiyou County road crew, during large storms, will often close the gate at McBride Springs along the Everitt Memorial Highway, as well as the road to Castle Lake. This is likely the case this weekend. 

Regions covered