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.


This Avalanche Advisory was published on April 11, 2011:


April 11, 2011 at 6:42 am

This morning, avalanche danger is LOW for all elevations and aspects. MODERATE avalanche danger may form on open, sun-exposed E-SE-S-SW-W aspects on slopes 35 degrees and steeper as the day warms up.


Forecast Discussion:


Some cloud cover developed over the mountains early this morning due to a weak low pressure system near the forecast area. These clouds should start to dissipate today as this system moves farther away. Dry, warm weather should continue as the region remains between weather systems. Some thin high clouds may develop tomorrow as another low pressure approaches the Pacific Northwest. Winds should remain out of the southwest and should increase some today. By tomorrow the winds should have decreased again. The forecast calls for daytime highs in the 40's above 7000 ft for today and tomorrow.

Observations:

Several wet point release slides occurred in the Mt. Rose backcountry yesterday afternoon on SE-S-SW aspects on Fireplug (photos), Incline Lake Peak (photos), and on Rose Knob Peak (photo). These slides only entrained the three to five inches of recent snow that had not been through much of a melt-freeze cycle. The old melt-freeze crust served as the bed surface. The largest of these avalanches ran for between 300 and 500 ft. None of these slides appeared to move enough snow to bury a person; however, they could have easily pushed someone off course into terrain traps that could have had other consequences. People triggered most of these point releases. A few of the smaller ones released naturally below exposed cliffs that concentrated the sun's heat.

On the northerly aspects on Incline Lake Peak, six to eight inches of soft unconsolidated snow still existed above an older melt-freeze crust. Observations showed significant signs of settlement on these aspects. Ski cuts on steep N-NE facing test slopes and layer bonding tests both indicated that this unconsolidated snow remains well bonded to the crust below it.

Primary Avalanche Concern: Warming Instabilities 

Enough melting should occur in the snowpack today for wet snow instabilities to form on sun-exposed E-SE-S-SW-W aspects due warmer temperatures and more sunshine forecasted for this afternoon. These instabilities should remain limited to the recent snow that has not undergone enough melt-freeze cycles to transition to consistent melt-freeze snow. This layer of recent snow will collect water as melting occurs today. As the water builds up in this layer, the snow will gain weight and lose strength. The increased winds and some cloud cover should help keep these wet snow instabilities limited to roller balls and wet point release slides. Some wet slab avalanches could also become possible on the most sun-exposed slopes.


The bottom line:

This morning, avalanche danger is LOW for all elevations and aspects. MODERATE avalanche danger may form on open, sun-exposed E-SE-S-SW-W aspects on slopes 35 degrees and steeper as the day warms up.


Andy Anderson - Avalanche Forecaster, Tahoe National Forest


Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:

0600 temperature: 24-28 deg. F.
Max. temperature in the last 24 hours: 34-42 deg. F.
Average wind direction during the last 24 hours: West southwest
Average wind speed during the last 24 hours: 15-25 mph
Maximum wind gust in the last 24 hours: 37 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 101-168 inches

Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS

For 7000-8000 ft:

  Monday: Monday Night: Tuesday:
Weather: Mostly cloudy this morning becoming partly cloudy in the afternoon Partly cloudy Sunny
Temperatures: 41-47 deg. F. 18-25 deg. F. 43-49 deg. F.
Wind direction: Southwest West shifting to southwest after midnight Southwest
Wind speed: 10-20 mph with gusts to 35 mph 10-15 mph with gusts to 25 mph 10-15 mph in the afternoon
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Monday: Monday Night: Tuesday:
Weather: Mostly cloudy this morning becoming partly cloudy in the afternoon Partly cloudy Sunny
Temperatures: 35-41 deg. F. 16-23 deg. F. 35-41 deg. F.
Wind direction: Southwest Southwest Southwest
Wind speed: 20-30 mph with gusts to 55 mph 15-25 mph with gusts to 45 mph decreasing to 10-15 mph with gusts to 25 mph after midnight 10-20 mph with gusts to 30 mph
Expected snowfall: O in. O in. O in.