Eastern Sierra - Fri Apr 2 2010
Eastern Sierra avalanche advisory |
Increasing winds today and plenty of new snow to blow around keep the avalanche danger rating MODERATE in isolated areas in steep exposed alpine terrain. Human-triggered avalanches are possible on slopes steeper than about 35 degrees where these fresh wind slabs exist and LOW on most other slopes. |
Unusually cold temperatures for April and yesterday’s general decrease in winds sure helps keep the snow cold and skiing conditions good especially in sheltered glades and bowls. No natural slides have been observed or reported over the last two days in the Mammoth and June Mountain areas despite the strong winds and snow transport over the last two days.
With no natural avalanches observed and a couple of us getting out and doing ECT tests, the storm snow seems to be bonding to the old snow surfaces. However, slopes exposed to the wind, especially convex rolls off ridges, have wind slabs and breakable crusts just off the ridgetops. One observer who ski cut the steep entrance to a northeast facing gully off San Joaquin Ridge reported a small 4” slab released but did not move down slope- a small slab with no bed layer – all dressed up with no place to go. I did several ECT tests on the same slope in the Mammoth Lakes Basin with results.
Increasing winds tomorrow make me nervous about fresh wind slabs forming in exposed terrain. These wind slabs will be most common on east to north facing slopes below exposed ridgelines. Human-triggered avalanches are possible on slopes steeper than about 35 degrees where these fresh wind slabs exist and LOW on most other slopes.
Cold winter weather continues through at least Tuesday. Expects clouds, isolated snow showers and winds through the weekend. Temperatures will remian 10-20 degrees below normal for this time of year.
Clouds increase late this morning along with gusty west and southwest winds up to 75 mph over the ridgetops. Higher elevations might reach 30 F today and the upper 20’s on Saturday. Elevations from 8,000 to 9,500 ft might reach 40F today then upper 30’s on Saturday.
Another storm moves into the area by Sunday afternoon.
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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