Eastern Sierra - Fri Apr 9 2010
Eastern Sierra avalanche advisory |
The avalanche danger rating is LOW today. Generally safe avalanche conditions but watch for wet slides on east to south to northwest aspects below around 10,500 ft. Rocky ridges along gully walls are particularly suspect today because wet slides tend to start around rock outcrops. |
Many skiers and riders enjoyed stable snow conditions today in the Mammoth and McGee areas. Dry to damp powder is found especially in sheltered shaded lines above 9,000 ft. The snow turned to mushy but skiable wet snow from 7500 to 9,000 ft.
The most widespread avalanche activity today will be wet sluffs and possibly wet slab avalanches with sun and daytime heating. I expect a fairly rapid onset by mid to late morning in the Mammoth area with night time lows temperatures only reaching 28-30F. Instability begins on east, then south, through west and northwest facing slopes.
Based on observations from the Bishop area, wet slides will be able to entrain a lot of snow in steep terrain, running far and resulting in large, deep cement like debris piles that are nothing to fool with. Wet slides have occurred on the steep southeast slopes on Basin Mountain. Over the last three seasons, the southern slopes off Basin Mountain have been harbingers of wet snow activity in other areas. Snow on the northerly facing mid and low elevations will get a lot of energy today, especially if there are any high thin clouds this afternoon.
Avalanche conditions are generally safe and it is an appropriate time for informed backcountry travel in avalanche terrain. Techniques to manage risk: Watch for unstable snow on isolated areas such as big, steep, convex, wind-loaded slopes near ridge crests, and give cornices a wide berth when travelling on or below ridges. Cut the tops of steep slopes and cross-loaded gullies before skiing or riding. Pull over to another line periodically to let your sluff run by.
By this time of the year, most of us are tired of the wind. I am sorry to report that windy conditions are in the forecast for the next few days, just in time for the weekend. West and southwest winds picked up at the higher elevations by late morning yesterday. Windy conditions will continue and ridgetop gusts could reach 80 mph before the storm hits on Sunday. Elevations above 10,000 ft continue to be be 8-10 degrees above normal for one more day with daytime highs reaching the mid 40’s today. By Saturday, temperatues will fall to the mid 30’s and the upper 20’s by Sunday’s storm. Nights will get down to the low 20’s.
Mid elevations will be spared from strong winds until Saturday. 8,000 to 9500 ft elevations will see west wind gusting to 25 mph today and 40 mph on Saturday. It will be a scorcher today with highs in the low 50’s. Saturday will cool off to the mid 40’s, and by Sunday, high temperatures will be in the upper 30’s. Nightime lows at mid elevations will be in the 25 degree range.
A system just south of the Aleutian Islands will dig south with strengthening jetstream support. Where this storm will come onshore will determine how much snow we receive Sunday and Monday. Expect high clouds Saturday with low clouds on Sunday.
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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