Eastern Sierra - Thu Feb 25 2010
Eastern Sierra avalanche advisory |
Updated February 25, 2010 - 9:59 am
Update for the Mammoth area north to June Lake. Pockets of MODERATE avalanche danger persists on slopes greater than 35 degrees at higher elevations on wind loaded terrain, particularly below ridges on North East slopes. Also be alert for wet instability on solar aspects (East to South to Southwest) with the clear sunny skies and warm temperatures. |
Considerable snow fall Tuesday night and Wednesday, combined with moderate to strong winds and humid warm temperatures have created a thick dense slab of snow overlying a variety of surfaces. This is quite different than the light fluffy snow from the last storm that didn't form a slab. The Mammoth area accumulated the most snow with well over 2 feet in some areas,and even more in wind deposited areas. A trip out to Punta Bardini showed stable conditions this morning. No signs of shooting cracks, woomphing.Several pits dug showed moderate CT test scores in upper layers of snow pack (new snow), but ECT testsconsistently did not propogate. Ski cuts on steep slopes inone of the main gulliesgave no results.
Personal observations yesterday on Chicken Wing and Earthquake Dome revealed areas of unstable snowthat were skiier trigerable at mid to upper elevations onsteep convexities and especially below ridgelines on steep north-east slopes. Mammoth Mountain had widespread results from avalanche control work on the lower mountain yesterday morning, with slides being triggered suprisingly easily and running surprisingly far. Widespread small natural and skiier triggered slides were reported Inthe June area. Compression tests done by others in theMammoth area in the Scenic Loop and near Mammoth Rock. showed easy to very easy failures within thestorm layers. It is likely many of theseinstabilities have settled overnightand will continue tosettle today. Continue to use good judgement and slope assessment skills today in steeper terrain, especially where windloads exist and on convexities in steeper terrain.
Be especially alert on solar aspects in steep terrain near rocks where warming from the sun will likely have a signiificant affect on the new surface snow.
Partly sunny skies and warm temperatures, with lighter winds from the West can be 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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