Eastern Sierra - Sun Apr 18 2010
Eastern Sierra avalanche advisory |
The avalanche danger rating is estimated to be LOW this morning in the Rock Creek, Convict Canyon and Mammoth areas. By mid day, the avalanche danger increases to MODERATE on all slopes steeper than 30-35 degrees. There are no observations from the Bishop Creek area and with variable wet snow avalanche conditions reported from Rock Creek, Convict and the Mammoth area and the Tioga Pass area, there is little confidence estimating a danger rating for Bishop Creek. |
Many thanks to all the splitboard folks at Convict Lake last night! I received more observations than I get in a month. Most reports came from the Convict Canyon area with most parties seeing or starting small to large point release slides mostly above 10,000 ft on north, east, south and west aspects. Slides were running on 30 to 45 degree slopes. One slide started in winter snow off the top of Nevahbe Ridge and entrained enough wet snow on its 1,500 vertical feet drop to leave a good sized debris pile on the alluvial fan below. Rockfall was also reported and parties traveling on steep slopes below cliffs should be alert to that unforgettable sound. Wet snow avalanches were also observed in east facing steep terrain above 10,000 ft yesterday in Rock Creek Canyon.
The tipping point seems to have been reached with enough days of solar radiation adding energy, raising snow temperature and melting enough snow to get things moving. Nights have been cool, though when temperatures reach the mid 40’s before noon, the snowpack reacts by getting weak especially around rocks and cliff bands. Cornices are a concern now and see Josh’s post regarding encounters with a cornice in Lundy Canyon.
Recent or new avalanche activity is a clear signal that a high degree of caution is required. Danger is generally minimal early in the day when temperatures are cool, the sun is not yet affecting slopes or cornices, and strong supportive melt-freeze crusts exist. Danger increases as temperatures rise, solar radiation intensifies, and surface snow becomes wet or slushy. If wet snow does not freeze overnight, all bets are off no matter what time of day.
Be prepared to alter plans, adjust routes to avoid avalanche terrain, or even turn around and go back if you see signs of increasing danger, such as more than 2-3 inches of wet/slushy surface snow, pinwheeling, and snowballing. Danger often increases more quickly and earlier on steep, high elevation, sunny slopes and ridgetop cornices than in lower elevation, shaded areas. A sluff, a loose wet slide, or a cornice failure from above could hit you or trigger an avalanche even if you are on a shaded slope that feels cold at the time. Be vigilant and keep an eye on what's going on above you at all times.
Above normal temperatures through Monday will drop on Tuesday then plummet on Wednesday by 20- 30 degrees. By Tuesday, winter temps return with highs in the upper 20’s and low 30’s. A significant weather change is in store beginning Tuesday and will continue for most of the week.
Clear skies and light southerly winds are the weather story today. Highs at the 8,000 to 10,000 ft elevations could reach the mid 50’s again today. Higher terrain will see highs in the upper 40’s. Sunday night’s lows will be in the upper 20’s to low 30’s. South winds will increase Monday with gusts around 45 in the higher terrain.
Numerous point release avalanches ranging from small to 1500 vertical foot runners. Ava's observed and triggered on north,east, south and west aspects yesterday in Convict Canyon. Recent wet slides also observed in upper elevations of Rock Creek and Duck Pass area.
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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