Eastern Sierra - Thu Feb 11 2010
Eastern Sierra avalanche advisory
Posted February 11, 2010 by Sue Burak
The avalanche danger is generally LOW. In wind loaded terrain on slopes steeper than 35 degrees, the avalanche danger rating is MODERATE, especially on northwest through east aspects. Avoid smooth pillows of snow on northwest to east aspects just below ridge crests. Human triggered avalanches are possible in steep terrain, and remember, it’s the small slabs that could get you today. Use extra caution on slopes steeper than 35 degrees with shallow, rocky areas or steep rollovers.
Yesterday afternoon, some drifting and wind transport was observed along the Mammoth Crest, the upper elevations of Rock Creek and the Tioga Pass area. Winds were blowing both from the southwest and northwest along the Mammoth Crest. The variable direction of the winds means you will need to watch for wind drifted snow and wind slabs on a variety of aspects. Wind stripped areas now exist just below ridgetops and below the entrance to many high elevation bowls and gullies. The upper part of the Negatives and some area off the Mammoth Crest already had some windstripped areas and slabby snow along and right below the ridgetops. Yesterdays’ and last night’s winds added new areas of wind drifted snow and fresh small wind slabs. Be suspicious of any steep slope with recent deposits of wind-drifted snow.
Observer reports from Chicken Wing area and our pits the last two days in the Mammoth Basin show a well bonded snowpack with lots of force required to get the snow to fracture. Shears are mostly ragged and poorly defined.
Farther south, a report from the Convict/Mt Morrison area highlights the potential for wet snow instability that will likely begin in earnest over the weekend. Mid February sun and clear skies will create surface instabilities like roller balls and wet snow point releases on east to west aspects. There could be a scenario where the avalanche danger from wet snow avalanches could be moderate on east to south facing slopes while the north, shaded slopes remain generally stable.
Yesterday’s weak system and last night’s weak system has moved into the Pacific Northwest. The building high pressure ridge will push the storm track farther north for the weekend and through most of next week.
By the middle of next week, the ridge becomes stronger and the area will see temperatures reach 5-10 degrees above normal with highs in the 50’s at the 8,000 ft level. The only weather excitement today will be strong westerly ridge top winds gusting to 60 mph. Temperatures at the 8,000 to 10,000 ft elevations will reach the upper 30’s today and by Saturday, temperatures will reach the low 40’s. Elevations above 10,000 ft will see partly cloudy skies and those strong west winds. Highs will be in the upper 30’s to low 40’s.
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.