Eastern Sierra - Fri Mar 5 2010
Eastern Sierra avalanche advisory |
Avalanche Awareness Night! Sat. March 6th, 6pm @ June Lake Community Center. Free.
Strong winds over the last two days have created potentially dangerous avalanche conditions on some slopes. The avalanche danger rating for Bishop Creek north to June Lake is MODERATE for steep convex terrain at mid to upper elevation on 1) north to east facing slopes below ridglines and 2) where snow has been deposited from cross-slope winds. LOW avalanche danger exists for lower elevations and areas sheltered from the wind. |
Strong southwest and west winds Wednesday night stripped many ridges on exposed northwest to northeast facing slopes. The winds removed most of the Friday night and Saturday’s snow and left a glazed snow surface on the north face of Kid Mountain. The wind stripped shallow ridges and crossloaded north to northwest facing gullies in the Aspendell area. Exposed areas in the Mammoth Basin were also wind blasted last night from southwest winds. After the storm moved east yesterday, northwest winds took over and snow banners extended far away from high ridgetops, dropping snow onto southeast aspects and stripping north facing bowls.
In areas that escaped strong winds, snowpack tests yesterday on Punta Bardini suggest the snow is relatively stable. However, if you think all slopes are stable, think twice. Stability tests represent tiny points on a slope. Tracks on a slope indicate only that it didn’t fail when someone rode or turned on that particular line at that time. For today, we expect touchy windslabs along exposed ridges and well as some crossloading on open bowls and in gullies.
The primary avalanche concern for today is windloading for all regions. Wind slabs will be abundant and still-sensitive in any steep drifted terrain. The secondary avalanche concern is weak snow at the bottom of the snowpack in areas south of Mammoth. I heard a report today of an entire slope whumpfing on the west side of Piute Pass. The weak layer has strengthened but it is not to be trusted. Evaluate slopes for possible trigger points - shallow, rocky areas, steep breakovers or wind-loaded areas where avalanches are commonly triggered. Expose only one person at a time, so you have the maximum number of people available for any search.
A shortwave ridge will give us pleasant weather this morning. The next system approaching the area late tomorrow will bring clouds by the afternoon. The next system currently digging south from british Columbia will work it’s way down the West Coast later today and tomorrow. The best chance for snow showers is Saturday afternoon and evening. Winds will be light to moderate from the north this morning, then veering to the south later today and Saturday.
High temperatures today will remain cool, reaching 30-32 F at the 8,000 to 9,000 ft elevations. Higher elevations will be cold with highs in the upper teens. Ridgetop winds wll gust up to 35 mph this afternoon.
Kid Mtn north side, crowns observed near ridgeline
Red Mtn: slab avalanche under ridgeline cornice, R2D3
Nevahbe Ridge, avalanche debris at the mouth of gullies off Nevahbe Ridge
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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