Eastern Sierra - Wed Feb 10 2010
Eastern Sierra avalanche advisory |
Snowfall over the forecast area last night varied from trace amounts south of Mammoth to over 5 inches in the Mammoth area and north. The avalanche danger rating is estimated to be MODERATE in wind loaded areas that received greater amounts of new snow. For areas that received an inch or two of new snow, the avalanche danger rating remains LOW. |
MAMMOTH AND AREAS NORTH
Last night’s snowfall was accompanied with strong winds at the higher elevations. Fresh deposits of wind drifted snow will be sensitive to skier and rider triggering today.
People are getting compression test results on a variety of layers both in the slab created in the Martin Luther King week of snow and the recent snow from the weekend. Snowpit stability test results and recent human triggered avalanches demonstrate that human triggered avalanches remain possible in isolated areas in steep windloaded terrain. A recent human triggered avalanche in east northeast facing terrain emphasizes this concern.
SOUTH OF MAMMOTH
Areas south of Mammoth received far less new snow last night. The snowpack remains shallow and with recent cold temperatures , conditions remain favorable for the weak layer at the bottom of the snowpack to persist. While it is unlikely that a person could trigger an avalanche on this layer, faceted snow is tricky and unpredictable. Despite this persistent weak layer, the main avalanche concern remains windloading in steep rocky terrain.
ADDITIONAL DISCUSSION
The most recent weather forecast calls for a significant warming trend starting Thursday. This is good news for dry snow stability. However, it is likely the avalanche concern will shift to solar aspects (east to south to west slopes) where the sun’s energy will cause some melting of the snow surface and create wet snow instability.
Today’s weather will be sunny and cold. Expect daytime highs at 8,000 to 10,000 ft elevation to reach the upper 20’s to low 30’s. High elevations above 10,000 ft will be cold today with highs around 20F. Gusty northeast winds to 35-40 mph are expected over the ridgetops.
The big weather news is the strong high pressure ridge that will build over the West Coast beginning this afternoon. Daytime temperatures will rise into the 40’s by the weekend. The higher elevations will warm up also, with temperatures reaching well into the upper 30’s with lows in the upper 20’s. Any storms approaching the West Coast will affect the Tahoe area and northern California. Expect a long period of dry weather and mild temperatures through next week.
Skier triggered avalanche off San Joaquin 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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