Eastern Sierra - Sun Jan 17 2010
Eastern Sierra avalanche advisory |
The avalanche danger rating is estimated to be LOW today with isolated areas of MODERATE avalanche danger in steep windloaded terrain, mainly on northern slopes above 9,500 ft. Human triggered avalanches remain possibleand evaluate conditions on individual slopes before descending. Follow backcountry protocol by only putting one person in avalanche terrain at a time and clear the runnout zones. |
Main avalanche concern:
The main avalanche concern remains wind loading. Though warm temperatures and energy directed into the snowpack the last couple of days have promoted strengthening of the storm snow, there are isolated areas of instability in steep wind loaded terrain. Observers reported propagating cracks above a skier on an uphill traverse at the 10,000 ft elevation in the mountains around the McGee Canyon area. Fortunately, this was an isolated incident and no skier triggered slides occurred.
Second avalanche concern- faceted snow.
The snowpack ranges from 1.5 to about 2.5 ft. south of Mammoth in the Rock Creek and Bishop Creek areas. These areas have faceted snow throughout the pack and weak snow is more widespread than in the Mammoth area. Stability tests in the Bishop Creek area produced distinct shears with moderate to hard force in high elevation wind loaded terrain on Friday. Instability remains in isolated areas.June Mountain has a deeper snowpack but buried surface hoar was responsible for a large avalanche in an open area in the trees between 7,000 and 8,500 ft.
With heavy snowfall expected for the upcoming week, local avalanche professionals and experienced backcountry skiers and riders, expect natural avalanches to “clean out” a lot of weak snow in at least one widespread natural avalanche cycle. Despite a general housecleaning in avalanche terrain, new avalanche problems will arise.Expect the avalanche danger to dramatically increase by Monday night or Tuesday morning and remain high for the rest of the week.
Increasing clouds today herald the first of a parade of at least 4 storms developing across the Pacific. A very strong Pacific jetstream extends from near Japan to the eastern Pacific along a line to central California.
The first weak system pushes through this afternoon with storm energy focused north of our area. This is a good thing because rain is expected around Lake Tahoe Sunday night. The storm shears apart and the mountains around the Mammoth and June Mtn areas might see some snow accumulating this afternoon above 9,000 ft.
The National Weather Service has issued a Winter Storm Warning, beginning early Monday morning and continuing through early Tuesday morning. This is the first winter storm warning for our area in the new year. Expect over 2 feet of new snow to fall in the mountains around Mammoth and June Mountain. A Winter Storm Watch is in effect for elevations above 6,000 ft for the mountains in Inyo County, including Rock Creek and Bishop Creek. Snowfall amounts of 1 to 2 feet are expected above 8500 ft.
By Monday afternoon, strong southwest winds of up to 45 mph will affect the town of Mammoth, Aspendell and possibly June Lake. Ridgetop winds could exceed 100 mph by Sunday afternoon.
Today will be cooler than Saturday with high temperatures reaching the upper 30’s at the 8,500 ft elevation. Higher terrain will cool off another 5 degrees today, with highs in the upper 20’s.
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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