Eastern Sierra - Wed Jan 20 2010
Eastern Sierra avalanche advisory
Posted January 20, 2010 by Sue Burak
The Eastern Sierra Avalanche Center has issued a Backcountry Avalanche Warning for the mountains from June Lake to Bishop Creek. Two to three feet of new snow over the last 36 hours has fallen along with strong southerly winds. Snowfall and strong winds will continue for the next 24 hours. Today the avalanche danger is HIGH on all slopes. Natural and human triggered avalanches are likely. Avalanche terrain including avalanche runout zones should be avoided.
Southerly flow continues to produce equal opportunity snowfall amounts. Southern locations in the forecast area have received similar amounts of new snow and water as the Mammoth and June Mountain areas.
Strong southerly and southwesterly winds are common up and down the range. Elevations above 8,000 ft in Mono and Inyo counties experienced intense winds and high rates of wind loading all day yesterday. The June Mountain ski patrol released an avalanche on the Wall during control work- 4 hours a larger avalanche was released with over 3 feet of wind drifted snow forming the slab. Other slab avalanches ran on the rain crust from January 9th, all on the lower Mountain. In contrast, Mammoth Mountain patrol reported minor activity yesterday morning.
Since Monday, two to three of new snow has fallen. By the end of the week, another 2 to possibly 4 feet will be added to the snowpack. Once skies clear, the mountains will look completely different. In the meantime, high rates of new snowfall along with strong winds means windslabs are forming, natural avalanches are occurring and backcountry travel in avalanche terrain is not recommended.
The National Weather Service Reno and Las Vegas offices have issued winter storm warnings beginning today at 10 AM and continuing through Thursday night until 10 PM.
The biggest storm of the series arrives this morning. Heavy snowfall rates of up to 3” per hour are expected due to the intense uplift produced by the 100 mph jet stream. The position and speed of the jet create extremely unstable conditions that more than make up for the weaker orographic lift that is associated with southerly flow. Despite southerly flow, snowfall totals today and tonight are expected to range from 16-24” at the 8,000 to 9,000 ft elevations in Mono County. Two to three feet of new snow is expected above 9,500 ft today through Thursday night. Ridge top winds of 60-80 mph will continue with gusts over 100 mph this afternoon.
Mid elevations around Mammoth and Aspendell will see strong wind gusts over 45 mph today. It is possible the National Weather Service will issue a blizzard warning for Mono County tonight. For the mountains above Bishop Creek and the southern Sierra, another two feet of new snow is forecasted above 8,500 ft. Snow is expected in the Owens Valley by tonight.
Small to large avalanches running on rain crusts on June Mountain in the Carson, Nirvana and Face run areas.
Natural avalanches in the Narrows, Rock Creek Canyon
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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