Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Out of date — this forecast expired 10 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

After a short window of LOW danger early this morning, MODERATE danger will form on slopes steeper than 35 degrees on all aspects and elevations starting in the mid morning hours with the most sun-exposed aspects and progressing to other aspects during the day. Loose wet avalanches large enough to threaten backcountry travelers will be possible again today. Evaluate snow and terrain carefully. Identify and avoid the areas where wet snow deep enough for loose wet avalanches exists. 

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Even though temperatures remained well above freezing in most areas last night, clear skies should have allowed the snowpack to radiate enough heat into the night sky for some of yesterday's wet snow to refreeze. This thin refreeze will not last long, and the intense April sun and warm daytime temperatures will quickly melt through last night's refreeze leaving deep wet snow on the slopes. Once this happens, the ice bonds that give the snowpack strength will have melted away allowing the remaining loose wet snow to slide down steep slopes in the form of loose wet avalanches. Slopes steeper than 35 degrees on sun-exposed E-SE-S-SW-W aspects at all elevations will hold the best potential for loose wet avalanches since they should experience the most warming, but some of the NW-N-NE aspects could also see enough sun for wet snow instabilities to form at all elevations. Most of the wet snow instabilities should manifest as loose wet avalanches but other forms of wet snow instabilities like glide cracks or wet slabs are not impossible. 

    Once last night's melt-freeze crust starts to become unsupportable and the wet snow starts to deepen, it becomes unstable very quickly. As soon as the snowpack starts becoming unsupportable, it is time to move to more frozen aspects, onto lower angle slopes away from anything steep, or to get off the snow and start the BBQ on the beach. Stepping off your equipment and sinking into wet snow above your boot tops and small surface instabilities like roller balls, pinwheels, or point releases can provide clues that enough wet snow has formed for larger loose wet avalanches to become an issue. Terrain traps like gullies, creeks, and cliffs can greatly increase the risk of any size loose wet avalanches.

Avalanche Discussion

Yesterday observations on Rubicon Peak showed melt-freeze conditions on all aspects. The snow surfaces had already started to soften by 10 am on any sun-exposed slopes on all aspects and elevations. By 11:10 am the snow on northerly aspects had become wet and sticky as the melt-freeze snow softened and transitional snow below it also became wet. Sun-exposed east aspects held corn snow conditions above 8000 ft. with 2-3 inches of corn resting on top of a supportable melt-freeze crust at 11:30 am. At this time the overnight melt-freeze crust had almost become unsupportable on the east aspects below 8000 ft.

Reports of additional wet snow issues from 4/3 and 4/4 including loose wet snow avalanches in the Emerald Bay chutes and glide cracks on Pyramid Peak also came in yesterday evening. 

Regions covered