Eastern Sierra - Thu Mar 4 2010
Eastern Sierra avalanche advisory
Posted March 4, 2010 by Sue Burak and Josh Feinberg
Free Avalanche Awareness Night! Sat. March 6th, 6pm @ June Lake Community Center.
The avalanche danger rating for the Mammoth and June Mtn areas has increased from MODERATE to CONSIDERABLE for today. Over a foot of new snow has fallen, accompanied by moderate south and southwest winds over the ridgetops. The avalanche danger rating is CONSIDERABLE. Pay special attention to wind loaded areas and exposed terrain with big consequences if you trigger a slide.
The avalanche danger rating for Bishop Creek north to the Rock Creek area remains MODERATE. Snowpack variability exists across the region. Use good assessment skills on slopes greater than 35 degrees.
It has been a couple of interesting days since the storm moved out of the area on Sunday. Several parties reported whumpfing on Sunday, Monday and Tuesday in the Bishop Creek and Red Mountain area. There were no reports from the Rock Creek area. Compression and ECT tests in the Bishop Creek area collapsed on the old rounded depth hoar on east and north facing slopes at 8900 ft and 10400 ft.
The very first of several stability tests failed as the isolated column collapsed on the old depth hoar. However these test results were not repeatable in same pit or in nearby pits. With the huge amount of loading to the snowpack that occurred Friday night and Saturday, the whumpfing and collapsing columns are sure signs the snowpack has yet to adjust to the two to three feet of dense new snow.
Other stability tests have been performed at various elevations on Red Mountain and the North-East facing batch-plant bowl above Convict Dr. over the last 2 days. These have been showing weak layers existing at variable locations in the snow pack that have been failing and propagating with relatively clean shears with moderate to hard force (see recent observations for specifics). The clean planar shear qualities should be an indication to stay attentive and use good assessment skills for individual slopes that are steeper than 35 degrees, especially given all the variability that exists.
The primary avalanche concern for areas south of Mammoth to Bishop Creek continues to be wind loading due to yesterday’s and last night's winds south and southwest winds. Soft, shallow wind slab formation is likely to continue below ridges on north to east facing slopes in higher terrain.
The other avalanche concern for these areas with shallow snowpacks is the possibility of human triggered avalanches on the rotten, weak facets on the ground.
The primary avalanche concern for the Mammoth area north to June is wind loading on north to east facing slopes below ridgelines, especially at higher elevations. Over a foot of new snow above 9,000 ft and strong ridgetop winds means dangerous avalanche conditions exist from slab avalanches and point release sluffs which can entrain enough snow to take you for an unpleasant ride over cliffs or through trees.
Snow showers will wind down today as the low pressure system moves east and a short lived high pressure builds over the west coast. Today will be cool at the 8,000 to 9,000 ft elevations with highs reaching the upper 20's and low 30's. Higher elevations will be cold with highs only reaching 20 F.
Northwest winds will be light today, making for a great day of skiing.
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.
ESAC is operating on a limited budget and is supported by its members and the community. Please help support the Center by becoming a member today. Visit the Support area for more information.