Eastern Sierra - Fri Jan 29 2010
Eastern Sierra avalanche advisory
Posted January 28, 2010 by Sue Burak
The avalanche danger rating is estimated to be LOW in the June Lake and Mammoth areas. Isolated areas of MODERATE remain in steep wind loaded terrain. Avoid steep convex slopes, shallow snow near ridgelines in northwest to east facing terrain.
There is no data available for Rock Creek. In Bishop Creek from 8500 to 10,500 ft, the avalanche danger is estimated to be MODERATE on steep slopes greater than 35 degrees on all aspects due to persistent depth hoar.
Nights continue to be cold with gradually warming temperatures during the day. Solar energy directed into the snowpack is stronger than it was in December and early January. Snow is settling at a rate of about 2” per day. Total snow depth measured at the Mammoth Mountain ski patrol study plot has decreased from 105 to 90 inches in one week.
Daytime temperatures have warmed over the last few days and add to the strengthening of the snowpack. The high temperature yesterday at Tioga Pass (10,000 ft) was 45 F. Mammoth Pass, elevation 9,300 ft had a high temperature of 51F.
In the Mammoth Lakes Basin, the trend in snowpit stability tests above treeline indicates good stability. One observer dug a 7 ft pit on a 38 degree slope and did not find any reactive layers in his compression tests. There is a rain layer around 8,600 ft in the Mammoth Rock area from the January 12 drizzle that produced a few hard test results.
Low to mid elevation snow conditions in the June Lake area appear to be similar to observations reported from the Lee Vining Canyon area yesterday. Depth hoar and the January 12 rain layer are features common to both locations.
For areas south of Mammoth, including the Mt Morrison, Rock Creek and Bishop Creek watersheds, the shallow weak faceted snow at the base of the snowpack warrants a Fair snow stability rating. Snowpack stability varies considerably with terrain. Avalanche control work in the Bishop Creek area produced no results today. Despite the lack of control work results, don’t assume all steep slopes are stable. Depth hoar is unpredictable so use caution around potential trigger points such as shallow areas with sagebrush visible, rocky areas, steep breakovers, and wind loaded slopes.
It is important to evaluate individual slopes where you want to ride or ski- do you know how to tell the difference between safe and unsafe slopes? Take one of the many excellent avalanche courses offered locally and acquire some tools so you can tell the difference.
The avalanche danger is estimated to be LOW in the Mammoth Lakes and June Lake areas. There are isolated areas in steep, windloaded areas and convex rollovers where human triggered avalanches are possible. Evaluate conditions on individual slopes before riding or skiing.
This information does not apply to developed ski areas or highways. This advisory describes general avalanche conditions and local variations always occur.
Another weak splitting low pressure system moves into our area today. Skies will be mostly cloudy over most of the forecast area. Temperatures today will reach into the mid 30s and drop into the mid teens at night. Expect west to southwest winds to blow 5-15 mph and gust to 25 mph. Chance of light snow starting late Friday night into mid-morning Saturday, with up to an inch possible in some areas. Saturday will be colder with highs in the mid 20s with similar winds and similar cloud cover.
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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