Eastern Sierra - Sun Feb 7 2010
Eastern Sierra avalanche advisory
Posted February 6, 2010 by Josh Feinberg
Todays Avalanche Danger rating is estimated to remain at MODERATE with areas of CONSIDERABLE in wind loaded areas above tree line from North to East Aspects. Moderate winds above tree line have recently changed to veer more out of the North, which could result in wind loading on southern aspects throughout the day at higher elevations.
High water content of the 6-12” of new snow along with lots of energy directed into the snowpack from the clouds and the storm, helped yesterdays’ new snow to bond fairly well to the old snow surface throughout most of the region, especially below tree line and areas where the winds were light.
Observations:
North Lake: Parties skiing in alpine terrain on Saturday above North Lake reported no natural avalanche activity and stability tests in north facing terrain produced hard results on the old/new snow interface. These stability tests represent tiny points on one slope.
Red Mountain: A party skiing Red Mountain yesterday reported several loud woomphs and some small shooting cracks, enough to make them to feel safer turning around early.
Mammoth Area: Test pits and ski cuts yesterday on steep slopes from 8,000 – 10,000’ on Punta Bardini in open and confined terrain features revealed no instabilities in that area. However, Mammoth Mountain Ski Patrol reported wide spread avalanche activity during yesterday’s explosive control activity with crowns on the upper mountain ranging from 10” to several feet.
June Mountain: June Mountain Ski Patrol reported minimal results in area control operations.
Conclusion
Overall where wind loading was not significant the new snow seems to have bonded fairly well to the underlying snow. However, as Mammoth control operations revealed, NE wind loaded slopes about 10.500’ were very capable of sliding given the right trigger in the right spot. Some areas south of Mammoth with shallow snowpack were exhibiting signs of instability. From these observations we can conclude that variability exists across the forecast region. The MODERATE danger rating means human triggered avalanche are possible. Using ski tests and stability tests and knowing how to interpret the results will give you a better chance of avoiding a nasty ride. Keep your eyes open out there and continue to use careful slope assessment.
After receiving new snow overnight, the winter weather advisory expired at 4 AM this morning. After several days of southwest and west winds, winds have veered to the north as the small scale feature that brought upslope showers last night moved east.
North winds and scattered snow showers will continue for the next few days. Today will be cold and windy above treeline with gusts to 35 mph. Highs will only reach the 20F mark. With cloud cover, nights won’t cool off more than about 5-8 degrees to the low to mid teens. Elevations from 8,000 to 10,000 feet will see less north winds and highs in the mid to upper 20’s. Lows will be in 12-15F range.
By Tuesday, a cold but not very strong storm passes quickly over the area. The track of this cold storm is difficult to predict and the low sets up north or west of us more than 50 miles, will make the difference between getting 6-10” of new snow or nothing. The best chance for significant precipitation could occur by the end of the week.
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.