Eastern Sierra avalanche advisory
Posted March 17, 2010 by Josh Feinberg
Avalanche Awareness Night tonight (Wednesday), 6pm at the Mammoth Lakes Forest Service Auditorium across from the visitor's center. Free!
For Bishop Creek north to June Lake the avalanche danger rating is overall LOW with pockets of MODERATE developing on steep slopes greater than 35 degrees on East to South to South-West facing aspects as the sun warms and melts the snow surface.
Continued warm temperatures, very light winds and sunny skies will mean that the main avalanche concern for today will be wet snow instabilities on slopes greater than 35 degrees that face East to South to South-West. These will develop as the sun hits these slopes and has a chance to melt the surface snow. So far over the last 2 days only shallow surface instabilities have been observed. This doesn't mean that a deeper release is not possible. If you are planning to ski these slopes, play it safe and start early so you are off them before the surface melt reaches too deep into the snowpack. Also be wary of slopes with large cornices looming overhead which could break loose as the intense sun and warmth weakens them.
Observations over the last 2 days in the June Lake Area, Bishop Area, and McGee Creek Area all revealed scattered small shallow point releases occuring on these solar aspects, originating mostly near rock outcrops, at all elevations. At higher elevations (>10000') only the upper couple centimeters of surface snow was observed to be moistened by the sun, while the underlying snow is remaining dry. At lower elevations moist snow was found deeper.
Observations made at 12200' on an east aspect on Mt Tom yesterday revealed some areas of very shallow snowpack with the bottom 2/3 composed of very large and well developed facets. Compression tests resulted in moderately easy failures with very clean energetic shears. High elevation slopes with this kind of continental like snow pack structure may not be wide spread, but be on the lookout for them as they should be avoided.
Today will feel like spring- sunny, warm and only a few ridgetop breezes. But a storm will slide south along the back side of the ridge and bring colder temperatures and a strong north and northeast wind event for late Thursday.
By tonight there is a slight chance ofsparse amounts of new snow that could fall above 8500 ft.Convective thunderstorms are possible Thursday.
The weather event to plan around is the strong north wind event forecasted to occur Thursday night into Friday morning. Wind gusts over 60 mph should diminish by the afternoon on Friday. Temperatures will be cooler Friday but the weekend will be sunny and warm.
Sunny skies and mild temperatures are on tap for today. Highs at the 10,000 ft elevations will be in the low 40's with mild evening lows tonight in the upper 20's. Mid elevations will reach the 50's today. By Thursday, temperatures will fall 10 F for a brief return to winter.
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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