Eastern Sierra - Sat Jan 2 2010

Eastern Sierra avalanche advisory

Posted January 2, 2010 by Sue Burak

Updated January 2, 2010 - 9:51 am


Danger Rating: Low

The snowpack is gaining strength and the weather is forecasted to remain dry for at least a week. The avalanche danger rating is estimated to be LOW. There are generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human triggered avalanches are unlikely.

Hazard Assessment

In very isolated areas in extreme terrain, small avalanches are possible. The avalanche danger is estimated to be LOW on slopes where there is enough snow for an avalanche to occur. Continue to use caution and evaluate any steep slope where a stronger slab of snow exists over weak, sugary snow especially around rocks.

 

What a difference two days of high relative humidity and cloud cover made to the cold dry snowpack! Even though air temperatures have increased 5 to 10F, it is the combination of cloud cover and increased relative humidity that add energy to the snowpack and help the snowpack settle. The snowpack has settled 1 to 2 inches a day for the last two days at mid elevation stations like Mammoth Pass and higher terrain such as 10,000 ft Tioga Pass.

In the high alpine and on open features at ridgelines, the winds from Tuesday and Wednesday created some areas of windslab. Expect isolated firm windslabs near ridgecrests, on steep north and northeast aspects,or near terrain features. Fast old powder is still abundant in many treeline areas. Hard compression tests and rutschblock scores of 5-6 show very limited potential for skier-triggering.


A long fetch of moisture stretching from coastal sections near the CA/OR border to north and west of the Hawaiian islands can be seen at
http://squall.sfsu.edu/gif/sathts_pac_500_00.gif .

By the time the front makes it way this far south, it will be weaker, along with unfavorable flow for orographically enhanced precipitation. A high pressure ridge along the West Coast from Saturday into Sunday will bring dry conditions to the Eastern Sierra. The next opportunity for widespread precipitation appears to be more than 7 days out, close to the end of next week.

New Years Day will be cloudy in the mountains with a slight chance of snow. Highs at the 8,000 to 10,000 ft elevations will be in the upper 30's with lows in the mid 20's. Higher terrain will see highs in the upper 20's and lows in the teens. The wind returns today with moderate southwest winds 15-25 mph at mid elevations. The higher terrain will be hammered again with 35 to 50 mph average wind speeds with gusts to 90 mph.

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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