Lawinenlagebericht

Central Sierra Nevada

Sierra Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Human-triggered avalanches will be possible today as a result of new snow and strong shifting winds. New slabs of wind drifted snow could exist on any slopes near ridgelines, in gullies, or other open slopes exposed to loading from the SW or N winds. In more sheltered areas smaller soft slabs of storm snow may exist. MODERATE danger exists at all elevations.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Strong winds and new snow have created fresh slabs of wind drifted snow on wind-loaded slopes in near and above treeline areas. These wind slabs started forming yesterday and have not had time to bond to the snow below them. Human-triggered wind slab avalanches will be possible today. As the winds shift to the north during the day, they could move snow back across the ridges and build wind slabs on previously scoured slopes. Wind slab avalanches could involve enough snow to bury or injure a person. In addition to the wind slabs, fragile cornices will exist along ridgelines. 

    Blowing snow, cornices above a slope, wind pillows, and areas of smooth, firm, hollow-sounding snow can help identify where a wind slab may exist. Since the winds are forecasted to shift, the wind slabs will also move around and could exist on any aspect. Watch out for areas where slabs of wind drifted snow exist near ridgelines, in gullies, and on open slopes exposed to the wind.

    (2/19/2021) Blowing snow on Tamarack Peak yesterday before last night's new snow

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    The new snow may not have had time to bond to the old snow surfaces and some weakness may exist within the new snow due to changing conditions during the storm. Some areas may have gotten enough new snow for soft slabs of storm snow to form on top of these potential weaknesses. Other areas likely did not get enough new snow for problematic storm slabs to form. If storm slabs do exist today, most of them should remain small, but some larger ones may exist in areas where the most new snow has accumulated. This avalanche problem can exist in places that people gravitate towards on storm days like steep tree-covered slopes where collisions with trees and other terrain traps like narrow gullies can magnify the consequences of small avalanches.   

    Recent avalanche activity, shooting cracks, or punchy (dense over soft) feeling snow, can help identify where unstable storm slabs may exist. Pay special attention to steep convex rollovers in sheltered terrain in areas with deeper new snow. 

    (2/19/2021) Small shallow test slope failure on Tamarack Peak yesterday before last night's additional snow - Possible storm slab.

Avalanche Discussion

* Yesterday small shallow wind slabs and fragile cornices existed along ridgelines in the Tamarack Peak area (Mt. Rose backcountry). None of these extended very far away from the ridgelines but ski kicks and cuts in test slopes did trigger cracks and small failures. Snowpit tests also indicated that these new wind slabs were not bonding well to the old snow surfaces.

* A small test slope failure was also reported in more sheltered terrain on Tamarack Peak. Like small wind slabs, it did not involve enough snow to be problematic but was indicative of poor bonding between the new snow and old snow surfaces. 

* In the Carson Pass area observers reported light snowfall with limited accumulation and warm temps leading to heavy wet snow. Snowmobile cuts and other observations did not produce signs of instability other than a few rollerballs.  

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