THIS AVALANCHE FORECAST EXPIRED ON March 24, 2018 @ 6:49 am
Avalanche Forecast published on March 23, 2018 @ 6:49 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

CONSIDERABLE avalanche danger exists above 8000 ft and MODERATE avalanche danger exists in areas below 8000 ft. Today's avalanche problems include lingering wind slabs, loose wet avalanches, and possible deep slab avalanches. Daytime warming and strong March sunshine could make avalanches easier to trigger on sun-exposed slopes today.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Human-triggered wind slab avalanches will remain likely today on wind loaded slopes above 8000 ft. where most of the precipitation fell as snow. Some wind slab avalanches may remain possible in lower elevation areas exposed to wind-loading as well. Most wind slabs should exist in near and above treeline terrain on NW-N-NE-E-SE aspects but some could also linger on W aspects due to a more southerly component to the winds during the storm. Wind slab avalanches could be large and destructive. The strong March sun could also make some of these wind slabs easier to trigger on sun-exposed E-SE and W aspects. 

Use clues like recent wind slab avalanches, shooting cracks, cornices above slopes, ripples, drifts, or other wind created textures to help identify where wind slabs may exist and avoid those slopes in favor of more sheltered terrain or lower angle slopes. 

Avalanche Problem 2: Loose Wet
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Strong March sunshine may provide enough warming for some loose wet instabilities to form on sun-exposed slopes where new snow exists today. If enough warming does occur, rollerballs, pinwheels, and loose wet point releases should comprise the majority of the loose wet instabilities. While most of these wet snow instabilities should remain small, some could entrain enough snow to bury or injure a person. The strong sunshine may also make triggering an isolated lingering storm slab possible today as well.

Wet sticky surface snow, small pinwheels or roller balls, or recent wet snow avalanches represent some of the clues that warming instabilities are a problem. Avoiding wet snow issues means moving to shaded slopes where colder softer snow is likely to exist. 

Avalanche Problem 3: Deep Slab
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Deep slab avalanches that fail on the graupel / melt-freeze crust combination buried deep below the surface should have become more difficult to trigger, but some deep slabs may also remain possible today in some specific / isolated areas. East aspects above 9000 ft. in the Mt. Rose backcountry are the most suspect for deep slab activity, but observations prior to the storm found this layer in other places along the Sierra Crest as well. Significant uncertainty exists as to whether or not deep slabs still represent a problem for backcountry travelers. In many areas, this layer should be able to support the new load, but it is possible that in some places it cannot.  Due uncertainty surrounding this problem, deep slabs may be possible on any aspect with an east component (NE-E-SE) above 9000 ft. If a deep slab avalanche does occur today, it would be very large and likely unsurvivable. 

Due to the combination of uncertainty, a lack of data after the storm loaded the weak layer, and the catastrophic consequences of such an avalanche, deep slabs continue to warrant inclusion as an avalanche problem and avoiding slopes where even a remote possibility of a deep slab may exist is the best choice for today.

recent observations
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* An avalanche on Mt. Rose Highway closed the road yesterday. Details of the avalanche remain unknown.

* Skier triggered shooting cracks occurred on wind-loaded test slopes and on sheltered storm slab test slopes on Andesite Peak yesterday. 

* Large fragile cornices had formed above wind-loaded slopes on Andesite Peak. 

* Heavy rain and snow continued all day yesterday and ended between 7 pm and 11 pm. 

Weather and CURRENT CONDITIONS
weather summary

The storm dropped another 2.2 to 3.7 inches of water (some sensors reported over 4 inches of water) onto the forecast area yesterday before it departed the area last night. Most of this fell as rain below 7000 ft. and accumulated as 10 to 18 inches of heavy wet snow above 8000 ft. Storm totals since Wed. reached 4.5 to 8.4 inches of water with some areas reporting more than 9 inches of water. Above 8000 ft snow totals from this storm approached 21 to 36 inches of dense snow. The storm ended last night and clear dry weather should prevail through this afternoon. Clouds and winds should start increasing this afternoon as the first in another sieres of smaller but colder storms arrives over the area. The forecast calls for another 2 to 9 inches of snow between midnight and tomorrow afternoon. Strong southwest winds should also accompany this storm and snow levels should remain below 6000 ft. 

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 23 deg. F.
Max. temperature: 33 o 35 deg. F.
Average ridgetop wind direction: S to SW
Average ridgetop wind speed: 35 to 50 mph
Maximum ridgetop wind gust: 108 mph
New snowfall: Below 7000 ft: 2.2 to 3.7 inches of water | Snow above 8000 ft: 10 to 18 inches
Total snow depth: 88 to 115 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Sunny in the morning becoming partly cloudy during the day. Partly cloudy becoming mostly cloudy with scattered snow showers in the evening and widespread snow showers after midnight. Mostly cloudy with widespread snow showers
Temperatures: 33 to 39 deg. F. 21 to 26 deg. F. 27 to 32 deg. F.
Mid Slope Winds: Southwest Southwest Southwest
Wind Speed: 15 to 25 mph with gusts to 35 mph 20 to 30 mph with gusts to 45 mph 15 to 25 mph with gusts to 40 mph
Expected snowfall: 0 1 to 3 1 to 3
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Sunny in the morning becoming partly cloudy during the day. Partly cloudy becoming mostly cloudy with scattered snow showers in the evening and widespread snow showers after midnight. Mostly cloudy with widespread snow showers
Temperatures: 27 to 35 deg. F. 17 to 23 deg. F. 22 to 28 deg. F.
Ridge Top Winds: Southwest Southwest Southwest
Wind Speed: 30 to 45 mph with gusts to 55 mph increasing to 65 mph in the afternoon 30 to 45 mph with gusts to 70 mph 20 to 35 mph with gusts to 55 mph
Expected snowfall: 0 2 to 4 2 to 5
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