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 March 10, 2011:


March 10, 2011 at 7:33 am

Near and above treeline, avalanche danger is LOW with pockets of MODERATE danger on N-NE-E aspects on slopes 37 degrees and steeper. Elsewhere, avalanche danger is LOW. If snowfall amounts this afternoon exceed forecast expectations, avalanche danger will be greater and more widespread.


Forecast Discussion:


A storm system passing mainly to the north of the forecast area today will bring strong winds, cloud cover, and light precipitation to the region. Snow level is forecast at 7,000' for today. This is a fast moving system with almost all of the precipitation expected to fall this afternoon before the system exits the area overnight. New snow amounts of 1 to 3 inches are expected this afternoon along the Sierra Crest with the greatest accumulations north of Lake Tahoe. Very little to no precipitation is expected along the Carson Range on the eastern side of the forecast area. Air temperatures above 8,000' will reach their daily maximum this morning before slowly cooling through the afternoon hours. Ridgetop winds are increasing in speed this morning and are strong out of the southwest. Winds are forecast to remain out of the southwest and decrease to moderate in speed overnight into tomorrow.

Observations:

Thicker than expected cloud cover yesterday keep air temperatures at or below the lower end of forecast warming. As a result, minimal warming instability was observed. Observations made on Mt. Tallac (Desolation Wilderness area) and on Little Round Top (Carson Pass area) revealed melt-freeze snow surface conditions in nearly all sun exposed areas below 9,200'. Below 8,000' melt freeze conditions were noted in the top few inches of the snowpack on northerly aspects that receive low angle sun. Very limited skier triggered roller ball activity occurred on upper and lower elevation E-SE-S aspects and on lower elevation N-NE aspects. Above 8,500', stable snowpack conditions were observed on northerly aspects with well settled but still unconsolidated recent storm snow in shaded areas. Minimal wind transport was observed in most areas with the exception of significant blowing snow that was observed from a distance occurring on Pyramid and Dick's Peaks in the Desolation Wilderness area. (For pit profiles, photos, and more info click here.)

Primary avalanche concern: Storm snow

Specific to the Sierra Crest north of Lake Tahoe, pockets of storm snow instability are expected to form today in wind loaded areas. This will mainly occur near and above treeline on N-NE-E aspects below cornice features. By the late afternoon hours newly formed slabs 4 to 6 inches deep are possible. Natural avalanche activity is unlikely today, human triggered avalanches are possible. Recent warming has prepared the recent storm snow to receive rain below 7,000'. Rain on snow instability is not expected to occur today.

Secondary avalanche concern: Wind Slabs

In the vast majority of areas the existing wind slabs are stable. However, highly localized significant wind transport yesterday on the higher above treeline peaks will keep this concern ongoing. Very isolated human triggered hard slab avalanches remain possible above treeline on N-NE-E aspects that received significant wind loading yesterday. Avalanche size could range from small to large.


The bottom line:

Near and above treeline, avalanche danger is LOW with pockets of MODERATE danger on N-NE-E aspects on slopes 37 degrees and steeper. Elsewhere, avalanche danger is LOW. If snowfall amounts this afternoon exceed forecast expectations, avalanche danger will be greater and more widespread.


Brandon Schwartz - Avalanche Forecaster, Tahoe National Forest


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

0600 temperature: 28 to 34 deg. F.
Max. temperature in the last 24 hours: 32 to 45 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 44 mph
Maximum wind gust in the last 24 hours: 69 mph
New snowfall in the last 24 hours: O inches
Total snow depth: 93 to 129 inches

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

For 7000-8000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy skies in the morning. Mostly cloudy to cloudy skies in the afternoon with light snow near the Sierra Crest. Mostly cloudy skies with a chance of snow showers in the evening. Partly cloudy skies after midnight. Partly cloudy skies.
Temperatures: 34 to 38 deg. F. 18 to 25 deg. F. 32 to 36 deg. F.
Wind direction: SW SW SW
Wind speed: 20 to 30 mph with gusts to 50 mph. 20 to 30 mph with gusts to 50 mph. Winds decreasing to 10 to 15 mph with gusts to 25 mph after midnight. 10 to 15 mph with gusts to 25 mph.
Expected snowfall: Near the Sierra Crest 1 to 2 in. 0 to trace in. O in.

For 8000-9000 ft:

  Thursday: Thursday Night: Friday:
Weather: Partly cloudy skies in the morning. Mostly cloudy to cloudy skies in the afternoon with snow likely near the Sierra Crest. Mostly cloudy skies with a chance of snow showers in the evening. Partly cloudy skies after midnight. Partly cloudy skies.
Temperatures: Morning highs of 28 to 34 deg. F. 24 to 28 deg. F. 26 to 32 deg. F.
Wind direction: SW SW SW
Wind speed: 55 to 65 mph with gusts to 85 mph 45 to 55 mph with gusts to 70 mph. Winds decreasing to 25 to 35 mph with gusts to 55 mph after midnight. 20 to 30 mph with gusts to 45 mph.
Expected snowfall: Near the Sierra Crest 1 to 3 in. 0 to trace in. O in.