THIS AVALANCHE FORECAST EXPIRED ON March 23, 2018 @ 6:53 am
Avalanche Forecast published on March 22, 2018 @ 6:53 am
Issued by Andy Anderson - Tahoe National Forest - Sierra Avalanche Center

The avalanche danger is HIGH in near and above treeline terrain and CONSIDERABLE in below treeline terrain due to a complex mix of heavy snow, rain, wind, and changing snow levels. Natural avalanches are likely today and human triggered avalanches are very likely. Today's avalanche problems include wind slabs, storm slabs, and possible deep slabs.  Wet snow instability cannot be ruled out. Travel in, near, or below avalanche terrain is not recommended.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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Strong winds, intense snowfall rates, and significant new snow accumulation will create wind slabs on leeward slopes in near and above treeline terrain. The largest of these wind slabs will exist above 8000 ft. where more of the precipitation has fallen as snow, but some could form at lower elevations as snow starts to accumulate in these areas today.  Most wind slabs should exist on NW-N-NE-E-SE aspects but some could also form on W aspects due to a more southerly component to the winds. Natural wind slab avalanches are likely today, and human-triggered wind slab avalanches are very likely. Wind slab avalanches could be large and destructive. Some wind slabs could entrain some wet snow in areas where significant rain has fallen.

Avalanche Problem 2: Storm Slab
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The heavy snow from this storm has accumulated on top of lighter old snow and may not have had time to bond to this old snow surface. In addition, changes during the storm may create weaknesses within the storm snow that the intense snowfall expected today could quickly overload. Human triggered storm slab avalanches are likely today on steep sheltered slopes above 8000 ft. where more snow has and will continue to accumulate. Below 8000 ft. some storm slabs could also exist on slopes where new snow loads the slopes today. Some storm slabs could entrain some wet snow in areas where significant rain has fallen. In lower elevation areas where rain continues to fall, some loose wet avalanches may remain possible. 

Avalanche Problem 3: Deep Slab
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Deep slab avalanches also remain possible today. Prior to this storm tests and observations continued to indicate that a weak layer of graupel resting on a melt-freeze crust 2.5 to 5 ft below the surface could still fail. The storm has added a heavy load on top of the existing snowpack and could provide enough weight to trigger this deep slab problem or push it to the edge where the additional weight of a person on a slope could possibly trigger a deep slab. East aspects above 9000 ft. in the Mt. Rose backcountry are the most suspect for deep slab activity, but observations have found this layer in other places along the Sierra Crest as well. Due uncertainty surrounding this problem, deep slabs may be possible on any aspect with an east component (NE-E-SE) above 9000 ft.

The only effective deep slab management strategy is to avoid areas where a deep slab problem may exist. Avoiding aspects of concern, using slopes under 30 degrees on aspects of concern, and avoiding connected terrain where remote triggering could occur represent avoidance strategies.  Any avalanches associated with this weak layer would be large and have severe consequences. 

recent observations
Submit Observations

* A loose wet avalanche covered both lanes of Emerald Bay Rd. with up to 10 to 15 ft. of debris yesterday around 11:30 am. It released naturally.

* Large cornices and active wind-loading was observed on Tamarack Peak. Ski kicks and cornices pieces dropped on wind-loaded test slopes triggered shooting cracks in 12 to 14 inch deep wind slabs on these slopes.

* Ski kicks on steep slopes in below treeline areas sheltered from the wind on the far east ridge of Tamarack Peak triggered shooting cracks and one small storm slab failure about 6 to 8 inches deep yesterday afternoon. The failure layer was the interface between the heavy storm snow and the lighter snow that was on the surface before the storm.

Weather and CURRENT CONDITIONS
weather summary

In the last 24 hours, the forecast area has received 1.5 to 3 inches of water with Bear Valley reporting almost 4 inches of water. This brings storm totals to 2.3 to 4.7 inches with some areas reporting more than 6 inches of water. Below 8500 ft. most of this has fallen as rain. Above 8500 ft. places picked up 11 to 17 inches of new snow in the last 24 hours with storm totals of 13 to 21 inches. Snow levels started to fall overnight and snow has started accumulating down in areas near 7500 to 8000 ft in most places and lower in some places. Snow levels should continue to fall into the 7000 to 7500 ft. range today and then drop below 6000 ft. after midnight tonight. The atmospheric river should continue today with more heavy precipitation and strong SSW and SW winds. The forecast calls for another 8 to 16 inches of new heavy snow above 7000 ft today with up to 2 more feet on the Sierra Crest. Wind speeds in the 35 to 55 mph range with gusts around 100 mph can be expected along ridgetops. By tonight the temperatures, wind, and precipitation should all decrease significantly as the storm moves out of the area. Some snow showers could continue through the night, but only 1 to 5 inches of new snow is expected overnight. Tomorrow brings a break in the weather that should last through Friday 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: 30 to 34 deg. F.
Max. temperature: 34 to 39 deg. F.
Average ridgetop wind direction: Southwest
Average ridgetop wind speed: 40 to 50 mph
Maximum ridgetop wind gust: 103 mph
New snowfall: Rain: 1.5 to 3 inches | Snow above 8500 ft: 11 to 17 inches
Total snow depth: 80 to 105 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: Cloudy with rain and snow throughout the day and a slight chance of thunderstorms in the afternoon. Snow level between 7000 and 8000 ft. Mostly cloudy with snow in the evening. Snow decreasing after midnight. Snow levels 6500 ft in the evening and falling below 6000 ft after midnight. Partly cloudy
Temperatures: 32 to 37 deg. F. 19 to 24 deg. F. 32 to 38 deg. F.
Mid Slope Winds: South Southwest Southwest
Wind Speed: 20 to 30 mph with gusts to 50 mph. 15 to 25 mph with gusts to 55 mph decreasing to 45 mph after midnight 15 to 25 mph with gusts to 45 mph
Expected snowfall: Rain: 1 to 2 in. | Snow: 10 to 18 1 to 4 0
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: Cloudy with snow throughout the day and a slight chance of thunderstorms in the afternoon. Mostly cloudy with snow in the evening. Snow decreasing after midnight. Snow levels 6500 ft in the evening and falling below 6000 ft after midnight. Partly cloudy
Temperatures: 29 to 34 deg. F. 18 to 23 deg. F. 26 to 34 deg. F.
Ridge Top Winds: Southwest Southwest Southwest
Wind Speed: 35 to 55 mph with gusts to 100 mph 25 to 40 mph with gusts to 80 mph decreasing to 70 mph after midnight 25 to 40 mph with gusts to 60 mph increasing to 80 mph in the afternoon
Expected snowfall: 16 to 24 1 to 5 0
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