Eastern Sierra avalanche advisory
Posted March 10, 2010 by Josh Feinberg
Avalanche Awareness Night in Mammoth on Wed. March 17 at 6pm. Forest Service Auditorium (behind visitors center). Free.
For Bishop to June the avalanche danger rating for today is LOW for low to mid elevations with pockets of MODERATE at higher elevations where recent wind-loaded areas exist, especially below ridge-lines and cross loaded gullies. Be extra cautious toward the edges of these wind-slabs where they are thinner and easier to trigger.
The Main avalanche concern for today is wind-slabs. Moderate to Strong winds have prevailed throughout the forecast area over the last couple of days and nights. Directions have varied greatly, with periods of winds coming from the South-West and other periods coming from the North and North-East. This means that wind-slab formation has been occuring on diverse aspects, both below ridge-lines and across slopes. Up to 5 inches of new snow fell 2 nights ago in the heaviest hit areas (higher elevations around Mammoth). The loose snow from this smaller storm combined with the loose snow left over from the larger March 3rd-4th storm makes this wind transport and loading of snow possible. Steep higher elevation terrain below ridge-lines and in cross-loaded gully-like features are the most likely spots where these wind-slabs could be triggered. Be wary of steep open bowls as well, particularly where convexities exist. Remember, it is usually at the edges of these wind-slabs where they are less thick that they are more sensitive to triggering. While less likely, it could still be possible to find sensitive wind-slabs on similar terrain at mid elevations as well.
Sheltered areas where the snow has not been wind effected should first of all be safer, and second of all have better skiing conditions.
By Sue Burak
Winter weather is the forecast for today, followed by warmer temperatures and clear skies for Thursday. Today will be mostly cloudy with scattered snow showers in the morning and partly clearing in the afternoon. Two to three inches of snow is expected above 8500 ft.
As the storm moved into the area, strong and gusty southwest and west southwest winds picked up last night. Ridgetop winds today will be strong with gusts over 60 mph. Mid elevation winds will continue to blow 30 to 45 mph. Cold north winds will be the main weather story for later today. With high temperatures around 10 to 18F at all elevations above 8,000 ft., wind chills will be bitterly cold and below zero.
Drying and warming will begin Thursday. Thursday will be sunny with lighter winds. Friday will be the warmest day of the week, followed by a weak system on Saturday that might drop a couple of inches of 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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