THIS AVALANCHE FORECAST EXPIRED ON March 25, 2018 @ 6:58 am
Avalanche Forecast published on March 24, 2018 @ 6:58 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

MODERATE avalanche danger exists in near and above treeline terrain where human-triggered wind slab avalanches are possible today. Deep slabs have become an unlikely but not impossible problem. 

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Strong winds and heavy snow left firm stubborn wind slabs on wind-loaded slopes in near and above treeline terrain. Additional snow today and tonight should form new smaller wind slabs on top of the existing wind slabs. Human-triggered wind slab avalanches will be possible today on NW-N-NE-E-SE aspects. While new wind slabs should remain small, avalanches involving the older harder wind slabs could be large and destructive. These older hard wind slabs should also be more difficult to trigger, but if they do break they may break after a person has fully committed to the slope.

Recent wind slab avalanches, shooting cracks, cornices above slopes, firm hollow sounding snow, blowing snow, ripples, drifts, or other wind created textures can all help identify where wind slabs may exist. Use this information to avoid those slopes in favor of more sheltered terrain with softer snow or use lower angle slopes. 

Avalanche Problem 2: Deep Slab
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Deep slab avalanches that fail on the graupel/melt-freeze crust combination buried deep below the surface should continue become more difficult to trigger as the snowpack continues to settle and consolidate. This problem should be unlikely in most areas but it is not impossible in some isolated areas. East aspects above 9000 ft. in the Mt. Rose backcountry are the most suspect for deep slab activity, but some uncertainty still surrounds this problem. In the unlikely event that a deep slab avalanche were to occur today, it would be very large and likely unsurvivable. 

Due to the combination of uncertainty and the catastrophic consequences of such an avalanche, deep slabs continue to warrant inclusion as an avalanche problem. Making backcountry travel plans that avoid slopes where unlikely but not impossible deep slab problems may exist remains the best choice for today.

recent observations
Submit Observations

* Natural wind slab avalanches triggered by large cornice collapses occurred on the far east ridge of Tamarack Peak (Mt. Rose backcountry) yesterday. Natural wind slab avalanches also occurred in near treeline terrain on Hidden Peak (near Emerald Bay), these also likely occurred yesterday morning and were likely triggered by cornice collapses.

* Evidence of widespread avalanche activity during the storm on Thursday was reported from Mt. Judah (Donner Summit area), Incline Lake Peak (Mt. Rose backcountry), Tamarack Peak (Mt. Rose backcountry), Relay Peak (Mt. Rose backcountry), Dicks Peak (Desolation Wilderness), and the Blue Lakes area (near Carson Pass).  Some of these were very large. They included wind slabs and deep slabs. 

* Snowpit observations targetting the graupel/crust layer near the crown of an avalanche on the Proletariat (Mt. Rose backcountry) yesterday still yielded unstable results on this layer. 

* Observations from Powderhouse Peak (near Luther Pass), Hidden Peak (near Emerald Bay), and Tamarack Peak (Mt. Rose backcountry) yesterday all showed continuous wind transport and firm stubborn wind slabs in near and above treeline terrain. They also found significant signs of settlement in the storm snow and no signs of instability below treeline.

Weather and CURRENT CONDITIONS
weather summary

A series of small weak disturbances impact the forecast area through the weekend. The first of these will mainly go north, but could provide some snow showers and continued strong SW winds to the area. The forecast calls for 1 to 5 inches of snow today above 7000 ft. with the best chances for snow in areas north of Emerald Bay. The second wave should arrive tonight with the potential for 1 to 6 inches of snow above 7000 ft. across the forecast area. Winds should start to decrease some tomorrow afternoon. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 18 to 21 deg. F.
Max. temperature: 30 to 36 deg. F.
Average ridgetop wind direction: Southwest
Average ridgetop wind speed: 40 to 60 mph
Maximum ridgetop wind gust: 100 mph
New snowfall: trace to 1 inches
Total snow depth: 84 to 114 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy with scattered snow showers in the morning and widespread snow showers in the afternoon Mostly cloudy with widespread snow showers in the evening and scattered snow showers after midnight Partly cloudy with isolated snow showers
Temperatures: 28 to 34 deg. F. 12 to 18 deg. F. 26 to 31 deg. F.
Mid Slope Winds: Southwest Southwest Southwest
Wind Speed: 15 to 25 mph with gusts to 40 mph 15 to 25 mph with gusts to 40 mph 10 to 15 mph with gusts to 30 mph becoming light in the afternoon
Expected snowfall: 1 to 3 1 to 4 up to 1
For 8000 ft. to 9000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy with scattered snow showers in the morning and widespread snow showers in the afternoon Mostly cloudy with widespread snow showers in the evening and scattered snow showers after midnight Partly cloudy with isolated snow showers
Temperatures: 21 to 29 deg. F. 7 to 13 deg. F. 21 to 27 deg. F.
Ridge Top Winds: Southwest Southwest West
Wind Speed: 20 to 35 mph with gusts to 65 mph 20 to 35 mph with gusts to 65 mph decreasing to 45 mph after midnight 15 to 25 mph with gusts to 35 mph decreasing to 25 mph in the afternoon
Expected snowfall: 2 to 5 3 to 6 up to 1
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258