Eastern Sierra - Sun Apr 25 2010
Eastern Sierra avalanche advisory |
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The avalanche danger rating is estimated to be LOW this morning and increase to MODERATE by miday, depending on elevation and aspect. Avalanche danger increases to MODERATE when the snow surface melts and becomes unstable in steep north to west facing rocky terrain. |
As spring weather continues, so do wet snow avalanches. Conditions are stable in the morning with elevations above 10,000 ft dropping down to the low 20’s at night. The area around Mammoth Mountain is warmer at night and has higher daytime temperatures than other drainages at similar elevations. Expect the snow to become unstable earlier in the day than areas north and south.
In sheltered terrain on north facing aspects at elevations above about 10,500 ft, winter snow can still be found though it can be slabby or firm wind board. A report from the Powerhouse Chutes described firm wind slabs on steep north facing terrain above 9500 ft. The snow surface did not soften yesterday on that aspect. Josh found winter snow on the northern slopes off Old Man’s Bowl and the Bloody Couloir the last two days and reported wet snow slide activity on east and west facing terrain. The point release slides picked up enough snow along the way to dump debris piles several feet deep in the runout. On the days, east facing slopes were active in upper Rock Creek Canyon and Pine Creek with wet slides of all sizes occurring by mid day.
There are some huge cornices out there- the one on Mt Starr in Rock Creek Canyon overhangs an east facing gully about 20 ft. As warm spring like conditions continue for the next two or three days, cornices continue to weaken so pay attention to what is above you on the ascent and descent.
Pay as much attention to your field observations as these danger ratings. Be aware of your surroundings, use common sense, and retreat with sunshine and really warm temperatures, because the balance tips rapidly. Start early and plan to be out of avalanche terrain before the snow turns slushy & mushy.
It's easy to tell what's happening out there, but due to variability and the speed with which things can change, remember the danger ratings above reflect average conditions and may not indicate what's actually happening at any given time or place.
After a windy afternoon yesterday, winds will be light today as a short lived ridge builds over the West Coast. The communities of Mammoth Lakes and Aspendell could see highs around 60F today and lows around 30 to 32 F. Higher terrain above 10,000 ft will be in the mid 40’s today with lows dropping into the low 20’s.
By Monday, winds pick up dramatically in response to the jetstream moving into northern California and bringing a winter storm to the area by Tuesday.
West and east facing steep slopes above 10,000 ft.
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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