Eastern Sierra - Wed Mar 31 2010
Eastern Sierra avalanche advisory
Posted March 31, 2010 by Sue Burak

The avalanche danger is MODERATE today on all wind loaded slopes steeper than about 30-35 degrees. Human triggered avalanches are possible and small avalanches could be triggered on steep, north facing slopes with fresh deposits of wind drifted snow.




 

Yesterday’s and last nights storm produced 7-10” of new snow in the mountains around the Mammoth Basin and in the upper elevations of June Lake. Upper elevation temps stayed in the low to mid 20’s at most weather stations, and this morning temperatures are in the mid teens. Ridgeline winds were gusty during the past 24 hours, especially on Mammoth Mountain and Mt Warren where west to southwest wind gusts over 100 mph were recorded. Mid elevation lakes like Ellery Lake and Lake Sabrina recorded wind gusts over 50 mph. June Mountain ski patrol reported strong wind gusts producing low visibilities and difficulty staying upright.


Southerly aspects will likely stay frozen today at mid to upper elevations. There could be some decent dust on rock hard snow. North facing slopes have sensitive wind slabs and small human triggered avalanches are possible.

I skied on along a north –south trending ridge yesterday in Rock Creek in about 3-4 inches of dense new snow. The winds from the last two days scoured openings in the trees only to follow with dense slabby 1-2 ft drifts in sheltered areas. Small slabs easily popped off short slopes with ski cuts and columns slid off frozen weekend surface while isolating columns for ECT tests. Sensitive drifts will be most widespread along the higher ridgelines, but also exist where the winds worked down into the mid and lower elevations. Any drifts will be easy to trigger on steep slopes, so avoid any steep slopes with recent wind deposits, which will look smooth and rounded and feel slabby or sound hollow. Watch for pockety cross loading around sub ridges, mid slope breakovers and gully walls.

A return to winter this week brings strong winds and temperatures 15-20 F below normal for this time of year.

Daytime highs at the 8,000 to 9,000 ft elevations will be cool, around 24-28F. Tonight will be cold with lows around 8 to 12 F. West winds decrease today with gusts to 25 mph compared to yesterday’s 45 and 50 mph wind gusts. Snow showers continue through today and taper off tonight.

Above 9,000 ft today temperatures will be cold with highs around 15F and lows around 5F. Expect gusty west winds up to 45 mph continue for most of the day. Another couple of new snow could fall today in the higher terrain. For Thursday, winds clock around to the northeast. It will be cold with those northerly winds blowing around 35 mph. Highs will be around 18F at the higher elevations and only a few degrees warmer at 8500 ft with highs in the low 20’s.

Winds return on Friday with only a chance of snow expected. A stronger storm reaches the eastern Sierra by Sunday. The return to spring weather will occur by Tuesday of next 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.

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