Eastern Sierra - Fri Feb 26 2010
Eastern Sierra avalanche advisory |
For the mountains from June Lake south to Bishop Creek, the avalanche danger this morning is estimated to be MODERATE on mid and upper elevation slopes with fresh deposits of wind-drifted snow from the Tuesday night/Wednesday storm. The avalanche danger rating will increase by late afternoon today as a powerful storm moves in and drops over 2 feet of heavy dense snow above 9,000 ft. Use extra caution on slopes steeper than 35 degrees in shallow, rocky areas or steep rollovers. |
On Thursday, freshly formed wind slabs from the Tuesday night/Wednesday storm were sensitive to skier triggering. There were numerous reports of small skier triggered slabs in steep and convex terrain in the Lakes Basin and June Lake region in open areas in the trees. A natural avalanche cycle occurred during the storm with both thin slabs and point releases observed in windloaded terrain on east to northern aspects, examples of which can easily be seen from the highway on McGee Mountain. For today, skier triggered slides are still possible in open areas in glades and in exposed higher elevation bowls. Strong winds this morning will transport more snow and avalanches involving recently wind-drifted snow are possible.
For southern regions down to Bishop, the main concern besides wind loading is the weak rotten sugary snow that exists at the base of the shallow snowpack in many areas. The dense new snow (over a foot at higher elevations) has added significant weight and strain to this weak snowpack structure. With the right trigger in the right spot, concern exists that a large avalanche could result. Unfortunately personal observations of this southern region were not able to be made for this advisory.
The approaching storm is impressive as seen http://squall.sfsu.edu/gif/sathts_pac_500_00.gif . The coiled comma shape and its location off the Oregon/California border is a good setup for significant snowfall later today and into Saturday. The only downside is this will be a warm storm and snowlines will start off high, probably just east of the town of Mammoth Lakes.
With over two feet of new snow coming in a short period of time, the avalanche danger will increase on Saturday. I expect very dangerous avalanche conditions by Saturday morning. Josh and I will be monitoring the storm carefully and will provide an update on Saturday. Expect widespread slab avalanche activity with very large avalanches in some areas.
After a mild winter day on Thursday, a warm winter storm will launch a direct hit on Mono County tonight and early Saturday morning. Though the storm is splitting, we will get the southern, more powerful branch of the jet and the Sierra from about Carson City north will be left out of the action. A Winter Storm Warning is in effect for both Inyo and Mono County later today through Saturday morning. Snow fall accumulations of over 2 feet area expected along the Sierra Crest with over a foot of snow expected at the 8500 ft level. Strong southwest wind gusts of 55 mph are expected at mid elevations from 8,000 to 10,000 feet. The communities of Aspendell and Mammoth could see gusts 55 to 65 mph this afternoon. Temperatures will be warm for a storm with highs in the mid 30’s today, falling to the low 20’s tonight. Higher elevations will be very windy with southwest winds from 55 to 80 mph with highs right around 32F. Hopefully temperatures will fall to the low 20’s tonight for the main snowfall event.
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.
ESAC is operating on a limited budget and is supported by its members and the community. Please help support the Center by becoming a member today. Visit the Support area for more information.
