Avalanche Advisory published on November 16, 2017 @ 5:34 pm
Issued by Brandon Schwartz - Tahoe National Forest

Early season conditions update #4

A deep slab avalanche problem has formed with human triggered avalanche activity in the Mount Rose portion of the forecast area. Feet of new snow continue to accumulate in some portions of the forecast area above 8,000' as the current storm progresses. Wind slab avalanche problems remain a concern area wide. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Large destructive avalanches are possible.

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Above Treeline

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Near Treeline

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Below Treeline
Avalanche Problem 1: Deep Slab
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This avalanche problem is currently believed to be specific to the Mount Rose portion of the forecast area. This geographic limitation is based on the limited collective snowpit data from around the forecast area pre-storm. This avalanche problem is known to exist on N and NE aspects where a layer of basal facets around 1 foot thick is at the base of the snowpack. Uncertainly exists as to presence/absence of this avalanche problem on NW aspects due to a lack of data. The lower elevation boundary of this avalanche problem is also uncertain due to a lack of available data but might be limited to areas above 8,500' to 8,700'.

A human triggered deep slab avalanche occurred today on Tamarack Pk in Hourglass Bowl, more info is available here. Numerous snowpit tests on other portions of Tamarack Peak today produced unstable results on the basal facet layer. Sensitivity to triggering for this avalanche problem is stubborn and it exists in specific areas. Signs of instability may not be readily observed prior to triggering an avalanche. Conservative terrain selection of slopes less than 30 degrees in steepness and/or avoidance of NW-N-NE aspects are sound mitigation techniques for this avalanche problem.

Avalanche Problem 2: Wind Slab
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Additional snowfall and strong to gale force SW winds will keep the concern for a wind slab avalanche problem ongoing throughout the forecast area. This avalanche problem is likely to exist in near treeline and above treeline terrain on NW-N-NE-E-SE aspects. Identify and avoid areas of wind drifted snow, especially below cornice features.

recent observations

-Human triggered deep slab avalanche reported in Hourglass Bowl on Tamarack Peak. NE aspect, 2 to 2.5 foot crown, failed on basal facets.

-SAC forecasters encountered numerous difficult to trigger (stubborn) but unstable snowpit tests on basal facets on N aspects on other portions of Tamarack Peak.

-Some signs of wind slab formation seen near treeline in wind loaded areas.

-Remote weather stations and manual observations in wind protected areas above 8,000' indicate 6 inches to 3 feet of new snow around the forecast area thus far from the current storm (as of 5 pm Thursday evening).

See specific observations below for more info.

Weather and CURRENT CONDITIONS
weather summary

Ongoing storm expected to taper off Friday. Sunny, warm, and dry this weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Thursday Thursday Night Friday
Weather: NA Cloudy skies with snow and rain in the evening. Widespread showers after midnight. Snow level 7,500' decreasing to 6,500' after midnight. Partly cloudy skies with scattered snow showers in the morning. Snow level below 6,000'.
Temperatures: NA deg. F. 24 to 29 deg. F. 33 to 38 deg. F.
Wind Direction: NA SW SW
Wind Speed: NA 25 to 35 mph with gusts to 70 mph. 15 to 25 mph with gusts to 50 mph in the morning, becoming light.
Expected snowfall: NA in. Likely 3 to 7 in | Possible 6 to 10 in. Up to 2 in.
For 8000 ft. to 9000 ft.
Thursday Thursday Night Friday
Weather: NA Cloudy skies with snow in the evening. Widespread snow showers after midnight. Partly cloudy skies with scattered snow showers in the morning.
Temperatures: NA deg. F. 22 to 27 deg. F. 29 to 34 deg. F.
Wind Direction: NA SW SW shifting to NW
Wind Speed: NA 35 to 55 mph with gusts to 90 mph. 30 to 40 mph with gusts to 75 mph, shifting and decreasing to 10 to 15 mph with gusts to 35 mph in the afternoon.
Expected snowfall: NA in. Likely 3 to 9 in. | Possible 10 to 16 in. 1 to 4 in.
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