Eastern Sierra - Wed Apr 28 2010
Eastern Sierra avalanche advisory |
The avalanche danger rating for the Mammoth area is LOW with isolated pockets of MODERATE for steep areas below ridges facing mostly North to East where small wind deposits can be found. The avalanche danger rating for the remainder of the forecast region from June Lake to Bishop Creek is LOW. Remember skier triggered avalanches are still possible during LOW danger ratings, continue to use good assessment skills and be on the lookout for areas of fresh hollow sounding wind slab. |
Last night and yesterday evening brought a few inches of dense new snow to the heaviest hit areas in the forecast region. Mammoth Mountain’s patrol site recorded 4 inches of new snow depth with just under 2 inches of water content. Other areas received much less. High winds out of the southwest accompanied this snow fall, with mid to upper elevation gusts exceeding 100mph. Unsettled weather continues for today with light precipitation and weaker yet still strong winds continuing out of the west-southwest. Another inch or two of snow is forecasted for the Mammoth Area, and less than a half inch forecasted for most of the remainder of the forecast area down to Bishop Creek. Expect temperatures to drop throughout the day.
Observations made yesterday evening around 6:30 in the Mammoth Area around Red Cone Bowl revealed 1-2 inches of dense new snow, mostly fallen in the form of graupel and heavily rimmed particles. Overall bonding of this new snow to the old snow surface was good. Strong winds had stripped most of the uppermost portion of ridge top slopes, especially west facing. Warm temperatures during this snowfall have helped with stability both in terms of bonding between snow layers and increasing the rate of bonding between snow crystals.
The main avalanche concern for today will be isolated pockets of newly wind deposited snow at elevations above 10,000’ on steep slopes facing north to East in: 1) areas which received the greatest amount of new snowfall, and 2) areas which were still holding wind transportable unconsolidated snow from the previous storm. These latter areas, although not widespread, could be found on some due north facing slopes at higher elevations (>10,000’).
The avalanche danger rating for the Mammoth area is LOW with isolated pockets of MODERATE for steep areas below ridges facing mostly North to East where small wind deposits can be found. The avalanche danger rating for the remainder of the forecast region from June Lake to Bishop Creek is LOW. Remember skier triggered avalanches are still possible during LOW danger ratings, continue to use good assessment skills and be on the lookout for areas of fresh hollow sounding wind slab.
After a dreary, rainy and wet snow day yesterday, expect more of the same today except for cooler temperatures. The main low is passing north with the jet staying over the Tahoe area which has delayed the onset of cold temperatures. The cold front will move into the area later today so expect snow levels to fall later in the day and this evening. Winds could remain high until the jet sags south and brings the cold front along with it. Another impulse coming from Oregon could lead to an increase in snow showers tonight.
Under clouds and windy conditions, temperatures at the 8,000 to 9500 ft elevations will reach the low to mid 30’s today. Higher terrain will be cold once the cold front moves in and high temperatures in the low 20’s are expected. Tonight will be cold with lows ranging from 15F to 8-10F at the mid to high elevations. Light snow accumulations could occur today along with strong west to southwest winds gusting to 60 mph over the ridgetops.
Cool temperatures and scattered snow showers are expected for Thursday and Friday with temperatures finally warming gradually for the weekend.
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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