THIS AVALANCHE ADVISORY EXPIRED ON April 1, 2014 @ 7:00 am
Avalanche Advisory published on March 31, 2014 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

MODERATE avalanche danger exists on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to lingering wind slabs and persistent slabs. Human triggered avalanches are possible in these areas. For all other areas avalanche danger is LOW.

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.

2. Moderate

?

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

Even though wind slabs should have become more difficult to trigger today due to settlement and consolidation over the last 24 hours, some human triggered wind slab avalanches may remain possible in heavily wind loaded areas. Most of these wind slabs should remain less than 2 ft in depth but some larger slabs that measure 2 to 4 ft in depth could exist in isolated areas. While wind slabs may exist on any wind loaded N-NE-E aspects and cross loaded NW and SE aspects, the most sensitive wind slabs will linger in places like couloirs, unsupported slopes, steep wind loaded terrain, cliffy areas, and other complex or extreme terrain. If wind slab avalanches occur on slopes where the near crust facets exist, they could step down to this older weak layer.

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

The loose weak layer below the old crusts (near crust facets) on the NW-N-NE aspects has 1-3 ft of snow on top of it in most places. As this new snow consolidates, it will become more slab-like while the near crust facets will remain weak. These changes may mean that breaking the near crust facets could become easier in days to come. Human triggered persistent slabs will remain possible in some areas on the NW-N-NE aspects above 8000 ft. where these near crust facets exist. Larger triggers like the wind slabs mentioned above, cornice failures, or multiple people on a slope are more likely to cause a failure in this layer. Any avalanches that fail on this weak layer will be large, involving all of the snow accumulated since March 25th. These kind of avalanches can fracture across longer distances and in areas that do not typically slide.

recent observations

Yesterday on Andesite Ridge where about 2 ft of new snow fell, small skier triggered cracking occurred in isolated areas and one small (6 inches deep) wind slab failed on a NE facing slope at about 7800 ft. Deeper in the snowpack, snowpit data indicated good bonding within the recent snow and between the recent snow and the old snow below it. The layer of weak loose snow (near crust facets) below the crust at the base of the recent snow was difficult to find here yesterday. Across Lake Tahoe on Tamarack Peak where only about 10 inches of new snow had accumulated, fewer signs of instability existed. Ski cuts, oven sized cornice drops, or aggressive jumping did not trigger shooting cracks or other signs of failures on wind loaded or non wind loaded slopes yesterday. However, snowpit data did reveal a well developed layer of near crust facets below the old crust layers on N-NE aspects. Tests on this layer consistently indicated that if it breaks the resulting crack can travel along the facets.

Weather and CURRENT CONDITIONS
weather summary

The forecast calls for continued below normal temperatures and an increase in cloud cover today as a cold low pressure system moves towards the region. The southwest winds should also start to increase. By this afternoon snow showers should begin around the region. The main part of this storm should arrive tonight and should bring another 4-8 inches of snow with temperatures in the teens to the area above 7000 ft. 3 to 6 inches of new snow is expected at Lake level. By tomorrow the system will move into NV and eastward, and snow showers, cloud cover, and winds should start to diminish.

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 18 to 24 deg. F.
Max. temperature in the last 24 hours: 27 to 33 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 20 to 25 mph
Maximum wind gust in the last 24 hours: 41 mph
New snowfall in the last 24 hours: Trace to 2 inches
Total snow depth: 46 to 72 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Cloudy with a slight chance of snow in the morning. Snow likely in the afternoon. Snow Mostly cloudy. Snow showers likely.
Temperatures: 26 to 33 deg. F. 12 to 19 deg. F. 24 to 31 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 10 to 15 mph with gusts to 25 mph increasing to 20 to 25 mph with gusts to 35 mph in the afternoon 15 to 25 mph with gusts to 35 mph 15 to 20 mph with gusts to 35 mph in the morning
Expected snowfall: up to 2 in. 4 to 8 in. up to 2 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Cloudy with a slight chance of snow in the morning. Snow likely in the afternoon. Snow Mostly cloudy. Snow showers likely.
Temperatures: 24 to 32 deg. F. 9 to 16 deg. F. 23 to 29 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 20 to 25 mph with gusts to 35 mph increasing to 30 to 35 mph with gusts to 50 mph in the afternoon 25 to 35 mph with gusts to 50 mph 25 to 30 mph with gusts to 50 mph decreasing to 15 to 20 mph with gusts to 35 mph in the afternoon
Expected snowfall: up to 2 in. 4 to 8 in. up to 2 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.