THIS AVALANCHE ADVISORY EXPIRED ON November 28, 2015 @ 6:48 am
Avalanche Advisory published on November 27, 2015 @ 6:48 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on all aspects in near and above treeline terrain on slopes 35 degrees and steeper due to presence of old hard wind slabs and smaller newly formed wind slabs. Human triggered avalanches remain possible today. Loose dry sluffs may remain possible on steep, sheltered, lower-elevation slopes as well. Evaluate the snow and terrain carefully before committing to a slope instead of letting the excitement of early season snow lead to poor decision making.

2. Moderate

?

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

2. Moderate

?

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

1. Low

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Strong NE and E winds along the ridge tops have scoured some of the snow away from wind slabs deposited during the recent storm and re-deposited it onto the NW-W-SW-S-SE aspects. The new wind slabs formed on these aspects will remain smaller and more limited in distribution, but more sensitive than the older wind slabs. Even though the winds may have scoured some snow away from the N-NE-E aspects, some wind slabs will still remain on these aspects as well. These older wind slabs have become more difficult to trigger, but stepping on or riding over trigger points or larger triggers like large cornices or two people on a slope would make triggering these wind slabs easier. More hard wind slabs will exist on these aspects as well. Like yesterday, wind slabs could exist on any exposed near and above treeline aspects today. Most avalanches that result from the failure of these wind slabs should fail at or above the old snow surface; however, some of them could step down into older snow layers in areas where the wind slabs exist on top of old hard slabs on the NW-N-NE aspects. Avalanches involving wind slabs could entrain enough snow to bury a person.

Cornices above a slope, wind ripples, drifts, blowing snow, hollow sounding snow, and other signs of wind loading can all serve as clues to help recognize slopes where wind slabs may exist. If a near or above treeline area looks nicely filled in and smooth and rounded, wind slabs likely exist in that area. Complex or extreme terrain like couliors and unsupported slopes will hold unstable wind slabs longer than other terrain and also have more potential consequences.

Avalanche Problem 2: Loose Dry
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Due to the continued cold weather, loose dry snow sluffs will remain possible today. Steep slopes in near and below treeline terrain on NW-N-NE-E aspects sheltered from the winds hold the best potential for these kind of instabilities. Most of these sluffs should only entrain some of unconsolidated snow in the upper part of the snowpack.

recent observations

Yesterday a report from Red Lake Peak indicated that small but sensitive wind slabs had formed as a result of wind loading by the E and NE winds. These small slabs remained isolated to areas near ridge lines. The report also indicated that weak snow still exists below the recent snow and still shows some signs of instability. Elsewhere this week observations indicated that wind slabs formed during the storm have become more difficult to trigger but that they may still fail with the right trigger. Tests on the wind loaded NW-N-NE aspects in areas where facets exist under old hard slabs still yield unstable results. Overall coverage remains thin and numerous rocks and other obstacles still remain very close to the snow surface and easy to hit.

Weather and CURRENT CONDITIONS
weather summary

Snow showers in the last 24 hours brought another trace to one inch of snow to the region. Cold unsettled weather will continue across the forecast area since the low pressure remains over the Great Basin. The forecast calls for continued north and east winds with daytime highs in the teens and overnight lows in the single digits above 7000 ft. Some light snow showers may continue today as well. Skies should become less cloudy and the winds should start to decrease over the next 36 hours. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 10 to 15 deg. F.
Max. temperature in the last 24 hours: 16 to 22 deg. F.
Average wind direction during the last 24 hours: Northeast
Average wind speed during the last 24 hours: 30 to 40 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: trace to 1 inches
Total snow depth: 15 to 24 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with scattered snow showers Mostly cloudy with scattered snow showers in the evening becoming partly cloudy with isolated snow showers after midnight Mostly cloudy with isolated snow showers
Temperatures: 14 to 21 deg. F. 3 to 9 deg. F. 15 to 22 deg. F.
Wind Direction: East East East
Wind Speed: 15 to 20 mph with gusts to 35 mph 15 to 20 mph 10 to 15 mph decreasing to 0 to 10 in the afternoon
Expected snowfall: up to 1 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Friday Friday Night Saturday
Weather: Mostly cloudy with scattered snow showers Mostly cloudy with scattered snow showers in the evening becoming partly cloudy with isolated snow showers after midnight Mostly cloudy with isolated snow showers
Temperatures: 9 to 16 deg. F. -1 to 6 deg. F. 11 to 18 deg. F.
Wind Direction: East East Southeast
Wind Speed: 20 to 30 mph with gusts to 40 mph 15 to 25 mph with gusts to 35 mph 10 to 15 mph with gusts to 25 mph in the morning
Expected snowfall: up to 1 in. 0 in. 0 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.