Eastern Sierra - Tue Jan 26 2010
Eastern Sierra avalanche advisory
Posted January 26, 2010 by Sue Burak
The avalanche danger is MODERATE on slopes steeper than 35 degrees in alpine terrain. The MODERATE danger rating means avalanche danger exists on some terrain features, particularly slopes steeper than 35 degrees and convex rollovers; human-triggered avalanches are possible on these slopes. Human triggered avalanches remain possible in steep trees in the June Lake area. Evaluate conditions on individual slopes before riding or skiing.
Monday’s moderate west and southwesterly winds transported snow and I expect small shallow slabs have formed near upper elevation ridgelines. Be on the lookout for these wind slabs if you’re up near ridgelines today.
Snowpack conditions vary widely over the area. Rollerballs were observed on north facing slopes in Bishop Creek last Sunday- dry snow was getting wet for the first time and indicates more serious wet avalanche danger could increase. June Lake received a rain/snow mix yesterday resulting in a nasty thick breakable crust below the Mid Chalet. The rain crust responsible for several natural and ski patrol triggered avalanches is now buried about 20 to 30 inches in open and treed terrain below 9,000 ft. A large natural avalanche occurred in Devil’s Slide a few days ago with trees in the runout zone still plastered with snow 4-5 feet above the snow surface.
To the south, the Rock Creek and Bishop Creek areas had shallow weak faceted snowpacks before last week’s storms dropped 3-4 ft of new snow. Last weekend, a widespread avalanche cycle occurred in steep north to east facing terrain above the South Fork of Bishop Creek Road. To the south of Bishop Creek Lodge, two very large and destructive avalanches started in wind loaded bowls and ran two thousand feet across the Bishop Creek Road and ended up in Bishop Creek. The avalanches all ran on the layer of depth hoar on the ground. The passage of time, increasing solar energy inputs to the snow and warming temperatures will slowly strengthen the weak snow, though how long this will take is uncertain.
Popular front country slopes in the Mammoth area are tracked out. There are no reports of skier triggered avalanches despite the mild weather and the number of people getting into the front country.
It is important to evaluate individual slopes where you want to ride or ski- do you know how to tell the difference between safe and unsafe slopes? Take one of the many excellent avalanche courses offered locally and acquire some tools so you can tell the difference.
A strong high pressure ridge begins to build over the west coast today and moves east Thursday evening. There is enough moisture in the higher levels of the atmosphere to keeps high clouds today. The ridge moves east Friday and the next trough nears the coast of California. Little precipitation is expected for our area because the trough shears with Tahoe receiving limited amounts of moisture. For today, expect partly cloudy skies with north winds around 15 mph at all elevations above 8,000 ft. North winds will increase this afternoon with gusty ridgetop winds 30 to 40 mph. Daytime temperatures could reach 40 F today above 8,000 ft. Tuesday’s highs were in the upper 30’s at many remote stations above 9,000ft and more of the same is expected today.
Please note that the avalanche danger rating in this advisory expires in 24 hours. This advisory is our best interpretation of snow pack conditions and NWS forecasts issued today. Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone exists between upper and lower elevations. Avalanches do not happen by accident and most human involvement is a matter of choice not chance. Most avalanche accidents are caused by slab avalanches that are triggered by the victim of member of the victim's party. Even small slides can be dangerous. Always practice route finding skills and carry avalanche rescue gear. Remember that avalanche danger ratings are only general guidelines. Distinctions between geographic areas, elevations, slope aspects and slope angles should be made.
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