Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Newly formed slabs of wind drifted snow, persistent instability, and springtime wet snow instability are all potential avalanche problems in the backcountry today. Rapidly changing weather conditions are expected again today with isolated thunderstorms possible this afternoon. Avalanche danger is MODERATE at all elevations.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Strong to gale force E winds last night will have drifted any snow available for transport in near treeline and above treeline areas. Potentially unstable new wind slabs are expected to exist near and above treeline where drifting snow has deposited on wind loaded and cross loaded SE-S-SW-W-NW-N aspects. Avalanche size up to D2 is possible.

    Look for signs of blowing and recently drifted snow, smoother surfaces, and pillows. Areas with the most recent deposits of drifted snow are where new wind slabs will be encountered. Sunshine on newly formed wind slabs may exacerbate instability today.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    There are some indications that the weak layer that has contributed to recent avalanches with persistent slab characteristics (wide propagation, failing with numerous previous tracks on the slope) is gaining strength. There is still uncertainty here with more data needed on weak layer stabilization of the barely faceted snow on the underside of the crust at the old/new snow interface. NW-N-NE-E aspects at all elevations hold lingering concern for avalanches failing along the crust located 1 to 3+ feet deep in the snowpack. Avalanche size is expected at D2 with up to D3 possible.

    This is a low likelihood, high consequence event and difficult to manage as conditions will seem stable right up until an avalanche occurs. The easiest tactic is to avoid the aspects of concern or entrench on sub 30 degree slopes without steeper slopes above or to the side.

     Photo: Monday's skier triggered avalanche on Relay Pk, NV with wide propagation and numerous previous tracks.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Warming today and periods of sunshine and solar radiation through and between the cloud cover will allow the strong April sunshine to create snow surface warming in wind protected areas on all aspects. This surface warming and melt will allow for the possibility of loose wet avalanches today in wind protected areas on all aspects. Avalanche size is expected at D1 to D2 depending on what the terrain is capable of producing.

    Rollerballs and pinwheels are indications of the presence of this avalanche problem. Consequences from even small loose wet avalanches can come from being pushed into or over rocks, trees, cliffs, and terrain traps below. Lower angle slopes can be used to avoid this avalanche problem. While wind exposed areas will likely have sufficient convective cooling to keep this problem from forming, anticipate how conditions will change away from the ridgetops and where wind protected areas will be encountered mid slope and below.

     Photo: Loose wet avalanches yesterday on Talking Mtn (Echo Summit area), N aspect around 8,100'.

Avalanche Discussion

* Snowpit data collected yesterday on Donner Peak and Mt. Judah (Donner Summit area) targeting the problematic weak layer at the old/new snow interface showed significant strength gains compared to what was reported from nearby Tressle Peak on Sunday.

* Multiple loose wet avalanches were seen occurring yesterday afternoon on the N side of Talking Mountain (Echo Summit area) at around 8,100'.

* A wind slab avalanche was reported yesterday from Tamarack Peak in near treeline terrain on a N aspect at around 9,600'. The avalanche was reported at around 65 feet wide and failed 4 to 12 inches deep within the recent storm snow.

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