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 10, 2011:


April 10, 2011 at 6:49 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:


Dry weather with warmer temperatures should prevail today due to a high pressure ridge over the area. Light west and southwest winds should accompany this high pressure today. A low pressure moving into the Pacific Northwest should allow some cloud cover to move in this afternoon. The winds and cloud cover should increase tomorrow as this low pressure moves farther inland.

Observations:

Yesterday, observations on Talking Mountain showed 10-12 inches of light snow resting on top of a hard, frozen, four to six inch thick crust on the N-NE aspects. Layer bonding tests indicated that this recent light snow has bonded to the crust below it. Ski cuts on steep test slopes only produced small loose snow sluffs that entrained the top three inches of the recent snow in this area (photo). Near and above treeline some east wind scouring had occurred on these aspects. On the more southerly aspects a thin, breakable sun crust existed at all elevations. Below this sun crust four to six inches of lighter colder snow remained on these aspects (photo). Tests on these aspects also showed good bonding between the old melt-freeze crust and the new snow above it. Ski cuts on steep SE-S facing slopes did not produce any signs of wet snow instabilities.

Primary Avalanche Concern: Warming Instabilities 

The forecast calls for temperatures to climb into the mid to upper 30's above 7000 ft. today. These warmer temperatures combined with the intense April sunshine will allow warmth to penetrate deeper into the snowpack. The most recent snow has not experienced much warming yet and does not have good drainage channels established through it. This layer of unconsolidated recent snow will collect the water that forms as the sun and warmth melt the snow. That water will make this layer heavier and weaker at the same time. Enough melting should occur for some wet snow instabilities to form on the sun-exposed E-SE-S-SW-W aspects during the day. These wet snow instabilities should remain limited to the recent snow above the old melt-freeze crust. Roller balls and wet point release slides should comprise the majority of the wet snow instabilities that form today; however, 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: 16-20 deg. F.
Max. temperature in the last 24 hours: 26-30 deg. F.
Average wind direction during the last 24 hours: West
Average wind speed during the last 24 hours: 15 mph
Maximum wind gust in the last 24 hours: 44 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 104-170 inches

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

For 7000-8000 ft:

  Sunday: Sunday Night: Monday:
Weather: Mostly sunny in the morning becoming cloudy this afternoon Mostly cloudy Mostly cloudy
Temperatures: 32-39 deg. F. 25-31 deg. F. 39-45 deg. F.
Wind direction: West Southwest Southwest
Wind speed: 10 mph 10-15 mph 10-20 mph with gusts to 30 mph
Expected snowfall: O in. O in. O in.

For 8000-9000 ft:

  Sunday: Sunday Night: Monday:
Weather: Mostly sunny in the morning becoming cloudy this afternoon Mostly cloudy Mostly cloudy
Temperatures: 32-38 deg. F. 22-28 deg. F. 33-39 deg. F.
Wind direction: West Southwest Southwest
Wind speed: 10-15 mph with gusts to 30 mph 15-25 mph with gusts to 35 mph 20-30 mph with gusts to 55 mph
Expected snowfall: O in. O in. O in.