Eastern Sierra - Tue Apr 6 2010
Eastern Sierra avalanche advisory |
Today’s advisory is in memory of Walter Rosenthal, Scott McAndrews and James Juarez who died on April 6, 2006 in a tragic accident on Mammoth Mountain. In addition to Walter’s many contributions to snow hydrology, he was dedicated to the idea of building an avalanche center to bring avalanche information to the eastern Sierra.
The avalanche danger rating is CONSIDERABLE today on all wind loaded north to south facing slopes steeper than 35 degrees. Skies will be clear, the snow deep, and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding, and conservative decision making will be essential for safe travel in avalanche terrain.All other slopes have a MODERATE avalanche danger. |
This was an equal opportunity storm with Mono and Inyo County stations reporting 1-2 feet of snow. Aspendell and Swall Meadows picked up 17-18” of new snow and Starlight Estates west of Bishop picked up a foot of snow. The highest storm totals were recorded at Mammoth Pass and Charlotte Lake in the southern Sierra, where 27-28” of snow fell in 24 hours.
One would expect that snowfall rates of 2-3” per hour and relentless winds would produce a widespread avalanche cycle. A surprising lack of natural activity was noted by observers around June Mtn, the southern end of the Sherwin Ridge and Rock Creek. McGee Mountain had two moderate sizes avalanches. Unless slopes cut loose last night and improved visibility adds to the number of observed naturals, this was a very unusual storm.
There are two avalanche concerns today. Wind slabs will be abundant and sensitive to human triggering in any steep drifted terrain. The other avalanche concern is today’s sunshine and warmer temperatures will be a shock to the snowpack. Good powder won’t last long once the sun’s energy reaches the snow and there is a possibility of wet sluffs and slides in steep terrain, both natural and human triggered.
It’s heads up out there today. Careful snowpack evaluation and cautious route finding are essential for anyone traveling at mid to upper elevations and on slopes steeper than approximately 35 degrees throughout this week.
Finally, a sunny day! Temperatures will climb about 5 degrees today and highs from the upper 20’s to 35 are expected from 8,000 to 10,000 ft. Higher elevations will see slightly higher temperatures than the last few days with highs in the mid 20’s.
As the low pressure moves east, northwest winds follow. Mid elevations get breezes with gusts to 30 mph. Wind transport of snow will continue in the higher terrain with northwest winds 20-30 with gusts to 55 mph.
As the ridge builds over the West Coast, winds will calm and temperatures rise. Wednesday will be the warmest day of the week and by Thursday, a storm tracking north of the area brings windy conditions.
Another weekend storm is lurking -however the storm may split and only the southern Sierra could see snow.
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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