Eastern Sierra - Wed Apr 7 2010
Eastern Sierra avalanche advisory |
The avalanche danger rating is MODERATE in steep wind loaded terrain on north to south facing slopes. Fresh wind drifted snow from strong north winds yesterday make southeast to south facing slopes the main slopes to watch today especially in alpine terrain. Look and think before dropping into steep windloaded terrain. Also watch out for point release wet slides on mid elevation southern aspects. |
Sunny skies, cool temperatures and moderate north winds were a welcome change from the weekend raging wind event. Snow banners created by north winds were common along the high elevations yesterday and people venturing into alpine terrain need to watch out for cross loaded slopes below north trending ridges and all south and southeast facing slopes off ridgelines.
Mid elevations were fairly calm yesterday and a few degrees of warming helped stabilize the storm snow. ECT tests produced ragged shears after pounding on the shovel and the only shear plane I found occurred when prying the block of storm snow off the column.
Several avalanche professionals commented about the lack of natural avalanche activity after the weekend storm. There was a natural slide off Climax during the storm and the Cliffs were running during the storm but control work Tuesday morning left a lot of holes and no propagation. Observers from the Mammoth area yesterday told of waist deep trail breaking and difficulty linking turns unless you had super phat skis or a snowboard. There was some shearing within the storm snow reported but no natural or skier triggered slides. Another observer described a layer cake structure in the new snow with less dense snow that fell as the storm began, followed by a dense middle layer during the heavy loading during the middle of the storm and lighter snow in the upper 8-12 inches of the new snow. No snow pit tests were done and stability was tested by skiing the slope.The main avalanche concern is triggering an avalanche in steep wind loaded terrain. With yesterday’s north winds, pay attention to southeast facing slopes at high elevations. Due to the incredible southwest and west winds during and after the storm, wind slabs on steep northern aspects at mid and high elevations could still be triggered by a skier or rider.
Calm weather and gradually warming temperatures are a positive influence on stability. On solar aspects though, another day of strong sun might melt enough snow to create a hazard from wet point release slides. For today, the avalanche danger rating is MODERATE. Natural avalanches are unlikely but human triggered slides are still possible in steep wind loaded terrain.
Today will be sunny and a little warmer than yesterday. The nuisance north winds will clock around to the east as high pressure ridge builds over us. Temperatures above 10,000 ft will be in the 35-40 degree range with easterly wind gusts to 25 mph. Mid elevations will see sunny skies, light easterly breezes and temperatrues in the mid to upper 40’s.
Thursday will be windy and partly cloudy as a short wave passes over southern Oregon.
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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