Eastern Sierra - Wed Apr 14 2010
Eastern Sierra avalanche advisory |
MODERATE avalanche danger exists today on steep North and North-East facing terrain just below ridge tops above 10,000’ where lingering wind slabs can be found. This especially pertains to the Mammoth and June areas which received greater amounts of new snow on Sunday and Monday than areas south to Bishop. The secondary concern is solar radiation heating up the new snow on East to South to West facing slopes at low to mid elevations. For other areas, the avalanche danger rating is LOW. |
Sunday night dropped 18” of new snow around Mammoth and 6-8” in areas south to Bishop. This snow was accompanied by strong SW winds which persisted through most of Monday, which formed sensitive wind slabs on North to North-East facing slopes particularly in steep exposed terrain just below ridgelines. Yesterday (Tuesday) was a beautiful sunny day with calm winds, and mild temperatures. These wind slabs are the primary avalanche concern for today. Observations and tests made in the Mammoth area yesterday on the exposed north face of Red Cone Bowl showed that these wind slabs are still sensitive to skier triggering. Click here for detailed report, tests and photos. Moderate avalanches resulted from control work yesterday morning on Mammoth Mtn, mostly scattered 1 foot crowns or less sliding in the storm layer. As more time passes these wind slabs will tend to stabilize. You should continue to use good assessment skills, especially on exposed steep north and east facing slopes, particularly at higher elevations and particularly in areas that received greater amounts of snowfall on Sunday night.
The secondary avalanche concern is wet instabilities. On steep east facing slopes in the lakes basin area of Mammoth many small wet point releases were observed originating just below rock bands. A decent sized wet point release was triggered away from rocks on a 40 degree east facing slope which widened to about 50 feet and ran abound 400 vertical feet. Click here for details and photos. The breezy conditions expected for today will likely decrease possible surface melt on slopes exposed to the wind. Areas to be on the lookout for wet instabilities today are sun exposed slopes (East to South to South-West facing) that aren’t exposed to the wind at low to mid elevations. These instabilities are likely to remain small, but as you can see from the slide detailed above, depending on the terrain there could be bad consequences.
Skies will be sunny today with breezy conditions at the higher elevations. The weather pattern won’t be active until Friday when a weak shortwave brings cooling and isolated snow showers Friday.
Warming will be gradual the next couple of days. With no ridge building overhead there is no mechanism to drive rapid warming. Southerly winds pick up today - mid elevations will have 10-15 mph winds with gusts to 30 mph. Higher elevation will have 10-20 mph winds with gusts to 35. Winds will pick up Thursday.
Temperatures will climb about 4 degrees today and another 3-5 degrees on Thursday. Daytime temperatures will reach the mid 30’s to low 40’s today at the 8,000 to 9,000 elevations. Higher terrain will be cool with highs in the mid 20’s to around 30F.
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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