THIS AVALANCHE FORECAST EXPIRED ON March 8, 2018 @ 6:55 am
Avalanche Forecast published on March 7, 2018 @ 6:55 am
Issued by Steve Reynaud - Tahoe National Forest

Moderate avalanche danger exists today due to deep slab and loose wet avalanche problems.  Triggering a deep slab avalanche is still possible on specific terrain features throughout most of the forecast area.  Evaluate terrain carefully and identify features of concern.

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.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Deep Slab
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A deep slab avalanche cycle has been occurring throughout the forecast area after starting during our last storm cycle.  Widespread, large, deep slab avalanches have occurred failing on a layer of faceted snow that formed in February.  Reports continue to come in from large avalanches that occurred during or just after the last storm cycle on NW-N-NE-E aspects at all elevations.  We have had at least 3 human triggered avalanche events with the last 2 happening on Sunday.  

This layer of buried facets will eventually gain strength over time and become non reactive.  That process has already begun in some areas.  In other areas, especially places with a shallower snowpack, recent snowpack tests continue to show unstable test results.  In terrain that has a shallow snowpack or where the weak layer is closer to the surface would be places a backcountry user could effect the weak layer.  Since the weak layer is deep, tracks on a slope do not necessarily indicate stability.  Possible trigger points could be rocks, trees, cliff areas, extreme terrain, and convex rollovers.  Triggering a deep slab avalanche has become a low probability but high consequence event.

Deep slabs are unpredictable and signs of instability may not be present.  The only effective management option is avoidance.  An avoidance strategy would mean staying off slopes steeper than 30 degrees and slopes connected to steeper terrain on NW-N-NE-E aspects.  Good recreation conditions currently exist on Northerly aspects that are below 30 degrees in steepness with no steeper avalanche terrain connected.  

Avalanche Problem 2: Loose Wet
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As daytime warming occurs, loose wet avalanche activity will become possible on E-SE-S-SW-W aspects at all elevations.  Increasing cloud cover and winds this afternoon should limited the amount of loose wet activity.  Most loose wet activity should be in the form of roller balls and pinwheels, but some larger loose wet avalanches are also possible.

Avoid steep sun exposed terrain as daytime warming occurs.

recent observations

* 3 human triggered Deep Slab avalanches have occurred over the last 4 days.  On Saturday, a skier triggered deep slab occurred on Schallenberger Ridge (Donner Summit area).  On Sunday, 2 deep slab avalanches occurred.  One in Negro Canyon (Donner Summit area) while digging a snowpit in lower angle terrain, and one at Lost Lakes (Carson Pass area) triggered by a snowmobiler.  All of these deep slab avalanches were at least D3 or above, all had wide propagation, with crowns ranging from 4 to 8' with one reported up to 15 to 20' deep in spots.

* Snowpack tests yesterday on Elephants Hump (Carson Pass area) showed consistent unstable test results on the buried facet layer on a deeply fractured slope.  This slope fractured, but did not avalanche, with cracks that went 500' wide from trigger point thought to have occurred on Sunday.

* Check out the observation page for more details on the widespread deep slab avalanche cycle.

* Warming effects have been reported throughout the forecast area on E-SE-S-SW-W aspects.   A small loose wet avalanche was reported from Incline Lake Peak on a SE aspect at 8800'.

Weather and CURRENT CONDITIONS
weather summary

Dry and mild conditions will continue today.  Increasing cloud cover and SW winds will occur this afternoon ahead of several weak systems passing through our area Thursday through the weekend.  Light rain and higher elevation snow is possible over the next several days.  A stronger storm remains possible for early next week.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 29 to 32 deg. F.
Max. temperature in the last 24 hours: 45 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 20 to 25 mph
Maximum wind gust in the last 24 hours: 34 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 59 to 86 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Partly cloudy. Slight chance of snow showers after midnight. Partly cloudy. Slight chance of snow showers in the morning. Slight chance of snow showers in the afternoon.
Temperatures: 44 to 49 deg. F. 27 to 32 deg. F. 43 to 49 deg. F.
Mid Slope Winds: SW SW SW
Wind Speed: Light winds becoming SW 10 to 15mph with gusts to 35mph in the afternoon. 15 to 20mph. Gusts to 35mph increasing to 50mph after midnight. 15 to 25mph with gusts to 50mph.
Expected snowfall: 0 Up to 1 Up to 1
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Partly cloudy. Slight chance of snow showers after midnight. Partly cloudy. Slight chance of snow showers in the morning.
Temperatures: 39 to 45 deg. F. 25 to 30 deg. F. 38 to 44 deg. F.
Ridge Top Winds: SW SW SW
Wind Speed: 15 to 25mph. Gusts to 30mph increasing to 50mph in the afternoon. 20 to 30mph with gusts to 50mph increasing to 30 to 45mph with gusts to 75mph after midnight. 30 to 45mph with gusts to 75mph.
Expected snowfall: 0 Up to 1 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

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